Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Effects of dry period length on onset of ovarian activity and ovarian cyclicity in the subsequent lactation
    Chen, Juncai ; Soede, N.M. ; Remmelink, G.J. ; Kemp, B. ; Knegsel, A.T.M. van - \ 2015
    - p. 230 - 230.
    continuous milking - progesterone - ovulation
    Negative energy balance (NEB) caused by high milk yield and insufficient feed intake in early lactation has been related to compromised cow health and fertility. Recent studies show that the NEB in early lactation could be alleviated by omitting or shortening dry period in dairy cows. It can therefore be hypothesized that omitting or shortening dry period improves fertility in dairy cows. The objective of this study was to evaluate the effects of dry period length on onset of ovarian activity and ovarian cyclicity in Holstein-Friesian dairy cows within 100 d in milk (DIM). The cows (60 primiparous and 108 multiparous) were
    randomly assigned to one of 3 dry period lengths (0, 30, and 60 d). Milk samples were collected 3 times a week for progesterone concentration analysis until 100 DIM after calving. Onset of luteal activity (OLA) was defined as the occurrence of at least 2 succeeding milk samples with progesterone concentrations ≥2 ng/mL. Normal resumption of ovarian cyclicity was defined as onset of first luteal activity occurring within 45 DIM, and followed by regular ovarian cycles of 18 to 24 d in length. Data are expressed as percentage or LSMEANS ± SEM. Within 100 DIM postpartum, cows with a 0-d dry period had greater incidence of normal resumption of ovarian cyclicity compared with
    cows with a 60-d dry period (53.2% vs. 26.0%; P = 0.01). Cows with a 30-d dry period tended to have greater incidence of normal resumption of ovarian cyclicity compared with cows with a 60-d dry period (47.7% vs. 26.0%; P = 0.09). In addition, cows with a 0-d dry period tended to have shorter interval from calving to first commencement of luteal activity (23.1 vs. 28.9 ± 2.0 d; P = 0.07) compared with cows with a 60-d dry period. Overall, our results demonstrate that omitting dry period improves resumption of ovarian cyclicity within 100 DIM in the subsequent lactation.
    Technical note: Evaluation of an ear-attached movement sensor to record cow feeding behavior and activity
    Bikker, J.P. ; Laar, H. van; Rump, P. ; Doorenbos, J. ; Meurs, K. van; Griffioen, G.M. ; Dijkstra, J. - \ 2014
    Journal of Dairy Science 97 (2014)5. - ISSN 0022-0302 - p. 2974 - 2979.
    dairy-cattle - monitoring rumination - automatic system - coefficient - agreement - ovulation - time
    The ability to monitor dairy cow feeding behavior and activity could improve dairy herd management. A 3-dimensional accelerometer (SensOor; Agis Automatisering BV, Harmelen, the Netherlands) has been developed that can be attached to ear identification tags. Based on the principle that behavior can be identified by ear movements, a proprietary model classifies sensor data as “ruminating,” “eating,” “resting,” or “active.” The objective of the study was to evaluate this sensor on accuracy and precision. First, a pilot evaluation of agreement between 2 independent observers, recording behavior from 3 cows for a period of approximately 9 h each, was performed. Second, to evaluate the sensor, the behavior of 15 cows was monitored both visually (VIS) and with the sensor (SENS), with approximately 20 h of registration per cow, evenly distributed over a 24-h period, excluding milking. Cows were chosen from groups of animals in different lactation stages and parities. Each minute of SENS and VIS data was classified into 1 of 9 categories (8 behaviors and 1 transition behavior) and summarized into 4 behavioral groups, namely ruminating, eating, resting, or active, which were analyzed by calculating kappa (¿) values. For the pilot evaluation, a high level of agreement between observers was obtained, with ¿ values of =0.96 for all behavioral categories, indicating that visual observation provides a good standard. For the second trial, relationships between SENS and VIS were studied by ¿ values on a minute basis and Pearson correlation and concordance correlation coefficient analysis on behavior expressed as percentage of total registration time. Times spent ruminating, eating, resting, and active were 42.6, 15.9, 31.6, and 9.9% (SENS) respectively, and 42.1, 13.0, 30.0, and 14.9% (VIS), respectively. Overall ¿ for the comparison of SENS and VIS was substantial (0.78), with ¿ values of 0.85, 0.77, 0.86, and 0.47 for “ruminating,” “eating,” “resting,” and “active,” respectively. Pearson correlation and concordance correlation coefficients between SENS and VIS for “ruminating,” “eating,” “resting,” and “active” were 0.93, 0.88, 0.98, and 0.73, and 0.93, 0.75, 0.97, and 0.35, respectively. In conclusion, the results provide strong evidence that the present ear sensor technology can be used to monitor ruminating and resting behavior of freestall-housed dairy cattle. Our results also suggest that this technology shows promise for monitoring eating behavior, whereas more work is needed to determine its suitability to monitor activity of dairy cattle.
    Cystic ovaries in intermittently-suckled sows: follicle growth and endocrine profiles
    Gerritsen, R. ; Laurenssen, B.F.A. ; Hazeleger, W. ; Langendijk, P. ; Kemp, B. ; Soede, N.M. - \ 2014
    Reproduction Fertility and Development 26 (2014). - ISSN 1031-3613 - p. 462 - 468.
    luteinizing-hormone - reproductive-performance - estrous behavior - dairy-cattle - lactation - estrus - pigs - estradiol - ovulation - cortisol
    This paper presents follicle development and hormone profiles for sows with normal ovulation or cystic follicles during an intermittent-suckling (IS) regime that started at Day 14 of lactation. Sows were subjected to separation from their piglets during blocks of 6 h or 12 h. In total, 8 out of 52 sows developed cystic follicles; either full cystic ovaries (n = 6) or partial ovulation (n = 2). Increase in follicle size of these sows was similar to that of normal ovulating sows until pre-ovulatory size at Day 5 after the start of separation, but from then on became larger (P <0.05). LH surge was smaller or absent in sows that developed (partially) cystic ovaries (0.4 ± 0.1 vs 3.6 ± 0.3 ng mL–1; P <0.01). Peak levels of oestradiol (E2) were similar but high E2 levels persisted in sows that developed (partly) cystic ovaries and duration of oestrus tended to be longer. The risk of developing (partly) cystic ovaries was higher when IS occurred in blocks of 6 h versus 12 h (33 vs 10%). In conclusion, the appearance of cystic ovaries at approximately Day 20 of ongoing lactation was related to an insufficient LH surge, as is also the case in non-lactating sows.
    The association of ruminal pH and some metabolic parameters with conception rate at first artificial insemination in Thai dairy cows
    Inchaisri, C. ; Somchai Chantsavang, ; Noordhuizen, J.P.T.M. ; Hogeveen, H. - \ 2013
    Tropical Animal Health and Production 45 (2013)5. - ISSN 0049-4747 - p. 1183 - 1190.
    body condition score - milk-production - holstein cows - acidosis - fertility - herds - cattle - yield - ovulation - lipopolysaccharide
    The objective of this study was to determine the association of metabolic parameters and cow associated factors with the conception rate at first insemination (FCR) in Thai dairy cows. The investigation was performed with 529 lactations from 32 smallholder dairy farms. At 3–6 weeks after parturition, blood samples and ruminal fluid were collected. Body condition scores (BCS) of cows were scored 1 week before expected calving date and at blood sampling date. Ruminal pH was measured at 2–4 h after morning feeding in ruminal fluid collected by ruminocentesis. Serum betahydroxybutyrate and serum urea nitrogen were measured by kinetic enzyme method. Cows with first insemination (AI) between 41 and 114 days postpartum were identified after pregnancy diagnosis for FCR. Breed, parity, interval from calving to first AI, BCS before calving, BCS after calving, loss in BCS after calving, SBHB, SUN, ruminal pH, and postpartum problems were selected as independent variables for a model with FCR as a dependent variable. A multivariable logistic regression model was used with farm as a random effect. Overall FCR was 27.2 %. The FCR depended on interval from calving to first AI, BCS before calving, and ruminal pH. The FCR between 69 and 91 days postpartum was significantly highest (45 %). Before calving, a cow with high BCS (=3.5) had significantly greater FCR than a cow with low BCS (=3.25; P
    Effect of different dry period lengths on milk production and somatic cell count in subsequent lactation on commercial Dutch dairy herds.
    Steeneveld, W. ; Schukken, Y.H. ; Knegsel, A.T.M. van; Hogeveen, H. - \ 2013
    Journal of Dairy Science 96 (2013)5. - ISSN 0022-0302 - p. 2988 - 3001.
    energy-balance - bovine somatotropin - metabolic status - holstein herds - short 35-d - cows - performance - yield - management - ovulation
    Shortening the dry period (DP) has been proposed as a management strategy to improve energy balance in early lactation. It is well known that both shortening and complete omission of the DP reduces milk production in the subsequent lactations. In most of these studies milk production data were obtained from planned animal experiments where cows were randomly assigned to DP length treatments, and cow management and diet composition did not differ among treatments. It may therefore be hypothesized that cows on commercial herds which apply a no-DP or short-DP-strategy, and support this by management adjustments, will have a less dramatic reduction in milk production. In this study, milk production and somatic cell count (SCC) following different DP lengths was investigated under commercial circumstances. Milk production of 342 cows (2,077 test-day records) was available from 5 Dutch commercial dairy herds which started a no DP-strategy for all cows. Test days of the year before applying the no-DP strategy are used as control (323 cows, 1,717 test-day records). Six other herds applied an individual cow approach and have different preplanned DP lengths within one herd. From these herds, information on 81 cows (482 test-day records) with a DP length between 0 and 20 d, 127 cows (925 test-day records) with a DP length between 21 and 35 d, and 143 cows (1,075 test-day records) with a DP length of more than 35 d was available. A generalized linear model incorporating an autoregressive covariance structure accounting for repeated test-day yields within cow was developed to estimate the daily yield (milk, fat and protein) and SCC of all cows. Applying no DP for all cows in the herd resulted in a reduction in postpartum milk production compared with within-herd control lactations (until 305 DIM) between 3.2 and 9.1 kg/d, which was a reduction of 12 and 32%, respectively. For the 6 herds that applied an individual cow approach with different preplanned DP lengths, the cow-specific DP strategy was based on milk production and SCC approximately 2 mo before calving. Cows with a preplanned DP length ranging between 0 and 20 d had a reduction in postpartum milk production between 5.7 and 13 kg/d compared with cows with a DP length of >35 d. Cows with a preplanned DP length ranging from 21 to 35 d had a numerically lower milk production (between 0.6 and 5.3 kg/d) than cows with a preplanned DP length of >35 d, but this difference was significant in only one herd. When corrected for milk yield, no difference in postpartum SCC for cows with different DP lengths was found.
    Timing of lactational oestrus in intermittent suckling regimes: Consequences for sow fertility
    Soede, N.M. ; Laurenssen, B.F.A. ; Abrahamse-Berkeveld, M. ; Gerritsen, R. ; Dirx-Kuijken, N.C.P.M.M. ; Langendijk, P. ; Kemp, B. - \ 2012
    Animal Reproduction Science 130 (2012)1-2. - ISSN 0378-4320 - p. 74 - 81.
    conventional housing systems - dietary energy-source - 2 feeding levels - reproductive-performance - luteinizing-hormone - primiparous sows - extended lactation - progesterone - pigs - ovulation
    Three intermittent suckling (IS) regimes were evaluated for their effects on lactational oestrus and subsequent fertility. Control sows were weaned (CW; n = 38) at d 26 ± 2 of lactation. In IS19-7D (n = 40) and IS19-14D (n = 42) sows, IS started at d 19 ± 1 of lactation and sows were weaned 7 or 14 d later. In IS26-7D (n = 41), IS started at d 26 ± 1 of lactation and sows were weaned 7 d later. During IS, sows were separated from their piglets for 10 h/day. Oestrus detection was performed twice daily without a boar and ovulation was confirmed by ultrasound once a week. In IS19-7D, IS19-14D and IS26-7D, respectively, 50%, 64% and 61% of the sows showed oestrus and ovulation during IS (P > 0.05), and, of the remaining sows, 100%, 93%, and 69% showed oestrus in the first week after weaning. In CW sows, 95% showed oestrus in the first week after weaning. Parity 1 sows were considerably less likely than older parities (23% vs. 68%) to show oestrus in lactation. Pregnancy rate of the first post partum oestrus (during lactation or after weaning) was 89% (CW), 92% (IS19-7D), 80% (IS19-14D) and 77% (IS26-7D) (P > 0.05) and subsequent litter size was 14.5 ± 0.5, 14.5 ± 0.6, 15.3 ± 0.5 and 15.2 ± 0.8, respectively (P > 0.05). Sows mated during lactation had similar pregnancy rate and litter size to those mated after weaning. Hence, ongoing lactation for the first 2–9 d of pregnancy did not negatively affect fertility. A total of 50–64% of IS sows showed lactational oestrus, regardless of the stage of lactation. Pregnancy rates and litter size were similar to control sows, and were not affected by stage of lactation at mating
    Cortisol profiles in sows submitted to an intermittent suckling regime compared with that of abruptly weaned sows
    Kluivers-Poodt, M. ; Gerritsen, R. ; Nes, A. van; Langendijk, P. - \ 2010
    Reproduction in Domestic Animals 45 (2010)3. - ISSN 0936-6768 - p. 377 - 382.
    to-estrus interval - luteinizing-hormone - primiparous sows - stress - reproduction - lactation - ovulation - piglet
    The aim of this study was to monitor changes in cortisol levels in sows around the time of separation from their piglets, in two different intermittent suckling regimes, compared with that in conventionally weaned sows. Sows were either weaned at 21 days of lactation (CONT) or subjected to an intermittent suckling regime (IS) from 14 days of lactation onwards. Sows in the IS regimes were separated from their piglets for 12 h every day, either from 08:00 to 20:00 hours (IS12) or from 08:00 to 14:00 hours and 20:00 to 02:00 hours (IS6). Separation caused a transient increase in cortisol levels on the first (CONT and IS12) and second (IS12) day of separation, compared with a gradual decline from early morning when the sows were still continuously suckling. In IS6 sows, in contrast, the transient rise in cortisol levels after separation at 08:00 hours was observed on the first 3 days and also on day 7 of the IS regime. Cortisol parameters were correlated with peri-ovulatory characteristics like onset of oestrus, onset of the LH surge and time of ovulation. Onset of the LH surge was delayed in IS6 sows. In conclusion, increase in cortisol levels as a consequence of separation of sows and piglets, is an acute, incidental phenomenon in IS12 and CONT sows, but shows a repeated acute elevation in IS6 sows, possibly placing IS6 sows at a higher risk of influencing peri-ovulatory processes and developing cystic follicles
    Post-weaning Altrenogest treatment in primiparous sows; the effect of duration and dosage on follicular development and consequences for early pregnancy
    Leeuwen, J.J.J. van; Williams, S.I. ; Kemp, B. ; Soede, N.M. - \ 2010
    Animal Reproduction Science 119 (2010)3. - ISSN 0378-4320 - p. 258 - 264.
    subsequent reproductive-performance - litter size - feed-intake - progestagen treatment - different patterns - lactating sows - in-vitro - ovulation - gilts - piglet
    Our objective was to investigate follicle development in sows during and after different Altrenogest treatments post-weaning and relate this to subsequent ovulation rate and embryonic development. Primiparous UPB sows (n = 47) were randomly assigned to (weaning = Day 0): control (no Altrenogest, n = 12), RU8-15 (15 mg of Altrenogest, Day-1 till Day 7, n = 12), RU8-20 (20 mg of Altrenogest, Day-1 till Day 7, n = 12) or RU15-15 (15 mg of Altrenogest, Day-1 till Day 14, n = 11). From weaning onwards, trans-abdominal ultrasound was performed daily. Sows were slaughtered on Day 4 or 5 after ovulation. Follicle size increased during Altrenogest treatment and reached a plateau around Day 6, regardless of dose (4.6 ± 1.5, 4.6 ± 1.6 and 4.6 ± 1.6 mm for RU8-15, RU8-20 and RU15-15, respectively). This increase resulted in larger follicles (P = 0.0002) at the onset of the follicular phase (i.e. time of weaning for control sows and 24 h after last administration of Altrenogest for treated sows); 4.8 ± 1.8, 4.8 ± 1.4, 4.9 ± 0.9 mm and 2.9 ± 0.8, for RU8-15, RU8-20, RU15-15 and controls, respectively. Pre-ovulatory follicle size tended (P = 0.07) to be larger for treated animals (7.9 ± 2.4, 7.9 ± 0.7, 8.6 ± 1.3 and 6.9 ± 0.9 mm for RU8-15, RU8-20, RU15-15 and controls, respectively). The interval follicular phase-oestrus was shorter (P = 0.005) for treated animals. Treatment did not affect ovulation rate or early embryonic development. However, for treated animals, the increase in follicle size during treatment was positively related with ovulation rate (P = 0.05). In conclusion, post-weaning treatment with Altrenogest of first litter sows influenced follicle size and shortened the follicular phase, but did not affect ovulation rate or early embryonic development.
    Synchronization and resynchronization of inseminations in lactating dairy cows with the CIDR insert and the Ovsynch protocol
    Bartolome, J.A. ; Leeuwen, J.J.J. van; Thieme, M. ; Sa'filho, O.G. ; Melendez, P. ; Archbald, L.F. ; Thatcher, W.W. - \ 2009
    Theriogenology 72 (2009)6. - ISSN 0093-691X - p. 869 - 878.
    timed artificial-insemination - unknown pregnancy status - estrous-cycle - nonpregnancy diagnosis - bovine somatotropin - progesterone insert - holstein cows - ovulation - ultrasonography - presynchronization
    Pregnancy per artificial insemination (AI) was evaluated in dairy cows (Bos taurus) subjected to synchronization and resynchronization for timed AI (TAI). Cows (n = 718) received prostaglandin F2a (PGF) on Days –38 and –24 (Days 39 and 53 postpartum), gonadotropin-releasing hormone (GnRH) on Day –10, PGF on Day –3, and GnRH and TAI on Day 0. Between Days –10 and –3, cows received a progesterone intravaginal insert (CIDR group) or no CIDR (Control group). Between Days 14 and 23, cows received a CIDR (Resynch CIDR group) or no CIDR (Resynch control group), GnRH on Day 23, with pregnancy diagnosis on Day 30. Cows in estrus (between Days 0 and 30) were re-inseminated at detected estrus (RIDE). Nonpregnant cows received PGF on Day 30 and GnRH and TAI on Day 33. Plasma progesterone was determined to be low or high on Days –24 and –10. Pregnancy rates were evaluated 30 and 55 d after AI. The CIDR insert included in the Presynch-Ovsynch protocol did not increase overall pregnancy per AI for first service (36.1% and 33.6% for CIDR; 34.1% and 28.8% for Control) but did decrease pregnancy loss (7.0% for CIDR and 15.6% for Control). The CIDR insert increased pregnancy per AI in cows with high progesterone at the time the CIDR insert was applied. Administration of a CIDR insert between Days 14 and 23 of the estrous cycle after first service did not increase overall pregnancy per AI to second service (24.7% and 22.7% for Resynch CIDR; 28.6% and 25.3% for Resynch control). For second service, RIDE cows had lower pregnancy rates in the Resynch CIDR group than in the Resynch control group. Cows with a CL (corpus luteum) at Day 30 had higher pregnancy rates in the Resynch CIDR group than those in the Resynch control group
    The effect of fenceline bull exposure on expression of oestrus in dairy cows
    Roelofs, J.B. ; Soede, N.M. ; Voskamp-Harkema, W. ; Kemp, B. - \ 2008
    Animal Reproduction Science 108 (2008)1-2. - ISSN 0378-4320 - p. 226 - 235.
    estrous behavior - cattle - ovulation - time - ewes - biostimulation - efficiency - signs
    The objective of this study was to investigate whether dairy cows visit and interact with a fenceline-housed bull more during oestrus than outside oestrus and whether fenceline bull contact affects expression of oestrus. At one end of a free stall a fence with vertical open bars was placed behind which a bull could be housed, allowing interactions with the cows. A closed fence with two blinded entrances was placed before the fence, creating a contact area. The experiment consisted of three treatments; it started with the control treatment (no bull on the farm) and was followed by bull treatment (a bull housed behind the fence) and no bull treatment (a bull present on the farm but not housed behind the fence). Signs of oestrus were observed every 4 h for 30 min and cows were equipped with pedometers. On the day of oestrus, cows were more frequent in the contact area during the bull treatment (12.0 ± 9.8 times) and the no bull treatment (13.9 ± 10.2 times) than during the control treatment (2.6 ± 2.5 times). The frequency of visits to the contact area was low and not different between treatments on the other days (2.2 ± 1.9 times). More cows had direct contact with the bull on the day of oestrus (71.4%) compared to the days outside oestrus (21.4¿30%). The duration of direct contact with the bull was highly variable between cows and did not differ between oestrus and non-oestrus days. Behaviour and duration of oestrus were not affected by treatment but the relative increase in number of steps during oestrus tended to be higher in the bull (5.5 ± 0.2) and no bull treatment (5.3 ± 0.3) than in the control treatment (4.6 ± 0.3). In conclusion, dairy cows in oestrus seem to be attracted by a bull or by the expectation of the presence of a bull, but fenceline bull exposure does not affect behavioural expression of oestrus.
    Peri-oestrus Hormone Profiles and Follicle Growth in Lactating Sows with Oestrus Induced by Intermittent Suckling
    Gerritsen, R. ; Soede, N.M. ; Langendijk, P. ; Dieleman, S.J. ; Hazeleger, W. ; Kemp, B. - \ 2008
    Reproduction in Domestic Animals 43 (2008)1. - ISSN 0936-6768 - p. 1 - 8.
    preovulatory lh surge - luteinizing-hormone - stimulating-hormone - prolactin secretion - progesterone concentration - litter separation - endocrine changes - primiparous sows - boar exposure - ovulation
    This study describes follicle dynamics, endocrine profiles in multiparous sows with lactational oestrus compared with conventionally weaned sows (C). Lactational oestrus was induced by Intermittent Suckling (IS) with separation of sows and piglets for either 12 consecutive hours per day (IS12, n = 14) or twice per day for 6 h per occasion (IS6, n = 13) from day 14 of lactation onwards. Control sows (n = 23) were weaned at day 21 of lactation. Pre-ovulatory follicles (¿6 mm) were observed in 100% of IS12, 92% of IS6 and 26% of C sows before day 21 of lactation and in the remaining 74% C sows within 7 days after weaning. All sows with pre-ovulatory follicles showed oestrus, but not all sows showed ovulation. Four IS6 sows and one IS12 sow developed cystic follicles of which two IS6 sows partially ovulated. Follicle growth, ovulation rate and time of ovulation were similar. E2 levels tended to be higher in IS sows (p = 0.06), the pre-ovulatory LH surge tended to be lower in IS12 (5.1 ± 1.7 ng/ml) than in C sows (8.4 ± 5.0 ng/ml; p = 0.08) and P4 levels were lower in IS12 and IS6 than in C sows (at 75 h after ovulation: 8.8 ± 2.4 ng/ml vs 7.0 ± 1.4 ng/ml vs 17.1 ± 4.4 ng/ml; p <0.01). In conclusion, sows with lactational oestrus induced by IS are similar to weaned sows in the timing of oestrus, early follicle development and ovulation rates, but the pre-ovulatory LH surge and post-ovulatory P4 increase are lower.
    The acute effect of bull presence on plasma profiles of luteinizing hormone in postpartum, anoestrous dairy cows
    Roelofs, J.B. ; Soede, N.M. ; Dieleman, S.J. ; Voskamp-Harkema, W. ; Kemp, B. - \ 2007
    Theriogenology 68 (2007)6. - ISSN 0093-691X - p. 902 - 907.
    suckled beef-cows - mature bulls - estrus - interval - ovarian - lh - progesterone - resumption - ovulation - duration
    The objective of this study was to investigate whether bull exposure affects LH profiles in postpartum, anoestrous dairy cows. Eight cows between 10 and 17 days after parturition were used. On Day 1, blood samples were taken at 10 min intervals for 8 h. On Day 2, blood sampling continued at 10 min intervals and after 2 h a bull was introduced behind a fence, and blood sampling continued for another 8 h. Time of resumption of luteal activity was between 25 and more than 80 days after parturition for these animals and was not related (P > 0.1) with frequency of LH pulses, amplitude of pulses and basal LH concentration on either Day 1 or Day 2. In 6 of the 8 cows, average and basal LH concentration were greater (P <0.001) during the 8 h of bull presence (0.56 ± 0.33 and 0.39 ± 0.26 ng/ml, respectively) compared to the 8 h without a bull (0.50 ± 0.30 and 0.35 ± 0.24 ng/ml, respectively). Pulse amplitude did not differ (P = 0.85) between Day 2 (0.45 ± 0.24 ng/ml) or Day 1 (0.45 ± 0.14 ng/ml). LH pulse frequency was greater (P <0.1) on Day 2 (5.3 pulses/8 h) compared to the Day 1 (4.6 pulses/8 h). In conclusion, fenceline bull exposure early postpartum seems to have an acute effect on LH-release in anoestrous dairy cows. Whether sustained bull exposure can hasten first ovulation after calving through an effect on LH release in dairy cows is an interesting area of research.
    Effect of Repeated Stress Treatments During the Follicular Phase and Early Pregnancy on Reproductive Performance of Gilts
    Soede, N.M. ; Roelofs, J.B. ; Verheijen, R.J.E. ; Schouten, W.G.P. ; Hazeleger, W. ; Kemp, B. - \ 2007
    Reproduction in Domestic Animals 42 (2007)2. - ISSN 0936-6768 - p. 135 - 142.
    postovulatory food-deprivation - hormonal profiles - salivary cortisol - female pigs - conceptus development - sows - ovulation - acth - estrus - secretion
    In pig husbandry, stress is being considered an important cause of impaired reproductive performance. Therefore, an experiment was performed to quantify effects of repeated stressors during the follicular phase and/or during early pregnancy on reproductive performance of gilts. Eighty-one cyclic gilts were assigned to one of four treatments, namely, stress treatment during the follicular phase (n = 20), stress treatment during early pregnancy (n = 20), stress treatment during both phases (n = 21) and no stress treatment (n = 20). All gilts were housed individually, but gilts in the stress treatments had no opportunity for visual or physical contact with other gilts. Further, animals in a stress-treatment were grouped for half an hour at the start of the treatment and during the treatment period nose-sling and an unpredictable feeding scheme were applied regularly. The extent of stress was monitored using heart rate measurements, behavioural observations and saliva cortisol levels during nose-sling fixation. Of the 81 gilts, 93% showed oestrus and were inseminated. Of these, 93% were pregnant at day 35, having 17.9 ± 0.3 ovulations and 15.6 ± 0.3 foetuses. These parameters were not affected by treatment. The stress treatment during the follicular phase tended to shorten cycle length (stress: 20.8 ± 0.20; control: 21.2 ± 0.17 days, p = 0.07) and weight of foetuses at day 35 (stress: 4.47 ± 0.08 g; no stress: 4.69 ± 0.08 g, p = 0.06); stress during early pregnancy did not affect any of the reproduction parameters. Percentage stereotypic behaviour, heart rate and saliva cortisol levels varied greatly between animals and between days, but did not differ between the treatments. No relationships were found between any of the reproductive parameters and any of the stress parameters (heart rate, cortisol, stereotypic behaviour). These results indicate that the repeatedly applied acute stressors did not generate a chronic stress-response and that these stressors during the follicular phase and/or during early pregnancy did not affect reproductive processes. It is not clear how these findings relate to suggested effects of stress(ors) on reproductive performance in pig husbandry.
    Influence of repeated regrouping on reproduction in gilts
    Soede, N.M. ; Sleuwen, M.J.W. van; Molenaar, R. ; Rietveld, F.W. ; Schouten, W.G.P. ; Hazeleger, W. ; Kemp, B. - \ 2006
    Animal Reproduction Science 96 (2006)1-2. - ISSN 0378-4320 - p. 133 - 145.
    repeated acute elevation - female pigs - hormonal profiles - salivary cortisol - sexual-behavior - early-pregnancy - induced stress - sows - estrus - ovulation
    It is generally assumed that stress around oestrus and during early pregnancy reduces reproductive performance of pigs. In our experiment, late prepuberal gilts (age at arrival 225 ± 6 days) were housed in groups of four. Stress treatment consisted of once weekly regrouping and twice weekly feed competition of the 28 Stress gilts during 6 consecutive weeks, starting 13 days after arrival. Control gilts (n = 28) were not treated. During the 0.5¿1.5 h after regroupings, Stress animals fought consistently more than the Control animals; up to 13 of the Stress animals fought for at most 60% of the time compared to one Control animal fighting for at most 3.3% of the time. The day before first regrouping, gilts had on average 4.0 ± 0.9 skin scratches. By week 6, this number had reduced to 2.1 ± 1.0 in Control, but remained 4.0 ± 1.3 in Stress gilts (P <0.05). In the afternoon after regroupings, skin scratches increased up to 6.3 ± 1.6 in the Stress gilts. Saliva cortisol in the afternoon before regrouping did not differ between weeks 1, 3 and 6, nor did it differ between Stress and Control. In Stress gilts, saliva cortisol was increased in the afternoon of first regrouping, in Batch 2 only (from 1.8 ± 0.4 to 4.1 ± 0.9 ng/ml; P <0.05). Animals showing a second oestrus within 5 weeks after arrival were inseminated. Duration of second oestrus of these animals was 2.48 ± 0.66 days in the Stress gilts (n = 24) and 2.21 ± 0.58 days in the Control gilts (n = 22; P > 0.10). At Day 35 after insemination, pregnancy rate was 100% in both groups. Ovulation rate and number of total and vital fetuses was similar (P > 0.10). The Stress treatment during a 6-week period around insemination consistently resulted in fighting but did not result in long term effects on cortisol levels and did not impair reproductive performance
    Effect of time of artificial insemination on embryo sex ratio in dairy cattle
    Roelofs, J.B. ; Bouwman, E.B. ; Pedersen, H.G. ; Riestra Rasmussen, Z. ; Soede, N.M. ; Thomsen, P.D. ; Kemp, B. - \ 2006
    Animal Reproduction Science 93 (2006)3-4. - ISSN 0378-4320 - p. 366 - 371.
    gender ratio - ovulation - spermatozoa - cows
    The objective of the present study was to examine whether different intervals between insemination and ovulation have an influence on the sex of seven-day-old embryos in dairy cattle. Cows were inseminated once with semen of one of two bulls of proven fertility between 36 h before ovulation and 12 h after ovulation. Time of ovulation was assessed by ultrasound at 4-h intervals. In total, 64 embryos were determined to be male or female. Of these 64 embryos, 51.6% were female. The sex ratio in the various insemination¿ovulation intervals (early: between 36 and 20 h before ovulation; intermediate: between 20 and 8 h before ovulation; late: between 8 h before and 12 h after ovulation) did not significantly differ from the expected 1:1 sex ratio (50, 50 and 55% females, respectively). Bull (Bull A and B) and Parity (primiparous and multiparous) had no influence on the expected 1:1 sex ratio either. The number of cell cycles was similar for male and female (P = 0.23) embryos when quality of the embryo (P <0.0001) was included in the model
    When to inseminate the cow? Insemination, ovulation and fertilization in dairy cattle
    Roelofs, J.B. - \ 2005
    Wageningen University. Promotor(en): Bas Kemp, co-promotor(en): Nicoline Nieuwenhuizen-Soede; F.J.C.M. van Eerdenburg. - Wageningen, The Netherlands : Wageningen University - ISBN 9789085042853 - 152
    melkvee - oestrus - kunstmatige inseminatie - ovulatie - bevruchting - diergedrag - gang - geslachtshormonen - geslachtsverhouding - dairy cattle - oestrus - artificial insemination - ovulation - fertilization - animal behaviour - gait - sex hormones - sex ratio
    Keywords: dairy cattle; oestrus; behaviour; pedometer; reproductive hormones; ovulation time; insemination strategy

    In dairy practice, calving rates after first insemination are often less than 50%. Part of this low percentage might be explained by wrongly timed inseminations. The aim was to establish the relationship between various oestrus characteristics and ovulation time in order to investigate whether these oestrus characteristics could predict ovulation time and to study the consequences of variation in the interval between insemination and ovulation on the success of fertilization and embryonic characteristics. The ultimate goal of the project was to come to an optimal insemination strategy that can be used in practice. The relationship between behavioural oestrous signs, changes in activity (measured by pedometers) and progesterone profiles and time of ovulation were. It was shown that monitoring progesterone profiles was not suitable to predict time of ovulation because of the large variation found in the decrease of progesterone relative to ovulation. Although the prediction of ovation time using behavioural oestrus signs was quite accurate, it seems not suitable for practice because of the high labour requirements. The increase in the number of steps measured by pedometers seems useful to predict time of ovulation accurately and could be easily implemented in practice. Effects of the interval between insemination and ovulation on success of fertilization and embryonic characteristics were also studied. It was shown that the insemination-ovulation interval in which high fertilization rates were observed was quite long (insemination from 36 to 12h before ovulation), while the interval in which the majority of fertilized ovum developed into a good quality embryo was considerably shorter (insemination from 24 to 12h before ovulation); the interval between insemination and ovulation did not affect the sex ratio of the embryos.

    In conclusion, the best chance to increase calving rates seems to be to use the insemination strategy, in which cows are inseminated between 5 to 17h after the first increase in the number of steps.
    Post-partum oestrusgedrag bij zeugen gaat niet gepaard met ovulatie
    Souren, N.Y.P. ; Langendijk, P. ; Soede, N.M. - \ 2005
    Tijdschrift voor Diergeneeskunde 130 (2005)17. - ISSN 0040-7453 - p. 502 - 507.
    varkenshouderij - zeugen - oestrus - diergedrag - lactatie - ovulatie - onderzoek - abnormaal gedrag - pig farming - sows - oestrus - animal behaviour - lactation - ovulation - research - abnormal behaviour - late-gestation - estrus - progesterone - plasma - diets - gilts
    Sows occasionally show oestrous behaviour within 5 days of farrowing: this is termed post-partum oestrus (PPO). This study investigated the incidence and possible causes of PPO on nine Dutch farms. Lactation records (n = 1374) were used, hack fat thickness was measured (n=25), and ovarian condition was assessed by transrectal ultrasonography. The incidence of PPO ranged from 0% to 62% on the different farms. On average, PPO started 59 hours after farrowing and lasted for 55 hours. Sows with PPO were younger than sows without PPO (parity 3.8 ± 0.2 v.v 4.4 ± 0.1, respectively; P <0.05) and had more back fat than sows without PPO (21.3 ± 1.2 vs 17.9 ± 1.2 mm, respectively: P <0.10). Occasionally, some follicle growth was observed in sows with PPO, but ovulation did not occur. PPO did not affect the weaning-to-mating interval or piglet mortality during lactation.
    Capacity of boar spermatozoa to bind zona pellucida proteins in vitro in relation to fertilization rates in vivo
    Harkema, W. ; Visser, I. ; Soede, N.M. ; Kemp, B. ; Woelders, H. - \ 2004
    Theriogenology 61 (2004)3. - ISSN 0093-691X - p. 227 - 238.
    pig oocytes - insemination - sperm - ovulation - ultrasonography - sows - eggs
    The purpose of this study was to determine variation among boars in the percentage of sperm in an ejaculate that express enhanced binding of zona pellucida proteins during treatment for capacitation in vitro, and to determine whether this relates to fertilizing ability in vivo. Ejaculates (n=35) were collected from 12 boars. A sample of each ejaculate was treated for capacitation in vitro. During incubation, the zona binding ability of spermatozoa was assessed at regular intervals with fluorescein-conjugated solubilized zona pellucida proteins (FITC-sZP) and propidium iodide, using a flow cytometer. After incubation, a percentage of the sperm had enhanced FITC-sZP binding. The percentage of viable sperm with enhanced FITC-sZP binding, expressed as a percentage of the total sperm population, increased rapidly over the first 60 min and thereafter reached a plateau after 120–180 min. Averaged over all ejaculates, the percentage at 180 min was 46% (range 27–61%); this percentage was significantly different among boars. However, the variation between ejaculates within a boar was relatively small. There was no significant boar effect on the rate at which the percentage of viable cells with enhanced FITC-sZP binding reached the maximum. In ejaculates (n=14) from four boars (selected from the group of 12), we investigated the increase in the percentage of viable sperm with enhanced sZP binding during treatment for capacitation in vitro in relation to the ability to fertilize in vivo. Sows (n=44) were inseminated 4 h after ovulation with a suboptimal insemination dose (0.5×109 spermatozoa). Time of ovulation was determined using transrectal ultrasonography and sows were killed at 120 h after ovulation. The percentage of fertilized oocytes, embryo development, and numbers of accessory spermatozoa were determined. The percentage of spermatozoa that were viable and showed enhanced sZP binding after 180 min of incubation was 48±12% (range 28–56%). The percentage of fertilized oocytes was 85±27% and 64% of the sows had 100% fertilized oocytes. The percentage of sows with 100% fertilized oocytes correlated well (P=0.05, R2=0.98) with the percentage of viable spermatozoa with enhanced FITC-sZP binding after capacitation in vitro.
    Energy partitioning and reproduction in primiparous sows : effects of dietary energy source
    Brand, H. van den - \ 2000
    Agricultural University. Promotor(en): B. Kemp; J.W. Schrama; N.M. Soede. - S.l. : S.n. - ISBN 9789058082237 - 139
    zeugen - lactatie - diëten - energiegebruik - voedingsstoffenbehoeften - insuline - voortplanting - ovulatie - spenen - sows - lactation - diets - energy consumption - nutrient requirements - insulin - reproduction - ovulation - weaning

    Introduction

    As a result of extensive changes in pig husbandry in the last 50 years, nutritional requirements of especially lactating sows nowadays differ strongly from those of sows in the past. Although diets are optimized to meet the requirements, sows still loose body reserves during lactation. Especially in primiparous sows, losses of body reserves during lactation are severe. These sows have not reached their mature body weight and therefore need nutrients for body development. However, due to a limited feed intake capacity, lactating primiparous sows mobilize body fat and protein to meet their requirements for maintenance and milk production.

    In general, these losses of body reserves result in impaired reproductive performance after weaning. The number of sows that remain anestrous after weaning is considerable and in sows that show estrus, weaning-to-estrus interval (WEI) is prolonged, ovulation rate seems decreased and embryonal mortality is increased.

    Therefore, nutrition is an important factor for optimal reproductive performance, especially in primiparous sows. An intermediate between nutrition and reproduction is the hormone insulin. Insulin is associated with the pulse frequency of luteinizing hormone (LH), WEI, ovulation rate, and farrowing rate. Feeding level, exogenous insulin injections, and diet composition can affect plasma insulin concentration. Effects of dietary energy source on plasma insulin concentration and its relationships with reproductive performance are hardly investigated.

    This study was conducted in primiparous sows to investigate: 1) effects of two specific dietary energy sources (fat: less insulin-stimulating vs starch: more insulin- stimulating) fed during different parts of the reproduction cycle, on reproductive traits, and 2) whether effects of these dietary energy sources on reproduction are dependent on the metabolic status during lactation (induced by feeding level).

    Dietary energy sources and plasma insulin concentration (Experiment 1)

    To investigate effects of dietary manipulated plasma insulin concentration on reproductive performance, firstly diets had to be composed that differ in insulin stimulation. Therefore, an experiment was conducted in cyclic gilts in which three diets, differing in major dietary energy sources, were investigated in their ability to stimulate plasma insulin secretion (Chapter 1). The studied major dietary energy sources were tallow, maize starch, and maize starch plus dextrose. The diet with tallow gave only a slight postprandial increase in plasma insulin level. The maize starch diet resulted in a higher postprandial insulin concentration, but two hours after feeding the plasma insulin concentrations were not different between the diet with tallow and with maize starch. The diet with maize starch plus dextrose resulted in the highest postprandial insulin levels and remained at a higher level during approximately 4.5 h after feeding. Preprandial insulin concentrations did not differ between diets.

    Design Experiment 2

    Because the diet with tallow (fat) and the diet with maize starch plus dextrose (starch) gave the largest contrast in plasma insulin concentration, these two diets were used in a large experiment with lactating primiparous sows. Sows received either the fat- or starch-rich diet from farrowing up to d 35 of the subsequent pregnancy. During lactation, sows were fed either a high (44 MJ NE/d; 1050 g CP/d) or a low (33 MJ NE/d; 790 g CP/d) feeding level. This was done to study, in addition to the main effects, the interactions between dietary energy source and feeding level on energy partitioning and reproduction. Within each feeding level, diets were fed to be isocaloric and isonitrogenous. After weaning, all sows remained at the same experimental diet, but all received the same amount of energy and protein (from weaning to estrus: 31 MJ NE/d; 740 g CP/d; from breeding to slaughter: 17.5 MJ NE/d; 420 g CP/d).

    During lactation, energy and nitrogen balance were determined and blood samples were collected to analyze insulin and LH profiles. After weaning (day 22 after farrowing), additional blood samples were taken to analyze periovulatory profiles of estradiol, LH, and progesterone. Sows were inseminated each day of standing estrus and slaughtered on d 35 of pregnancy. Results obtained from this experiment are described in Chapter 2 to 5.

    Dietary energy source and energy partitioning (Experiment 2)

    Effects of dietary energy source and feeding level on milk production, milk composition, piglet body composition, and energy partitioning of lactating primiparous sows are described in Chapter 2. At the low feeding level no differences between the two dietary energy sources were observed for milk composition, body composition of the piglets, or energy and nitrogen balance of the sow. At the high feeding level, however, the fat-rich diet resulted in milk with a higher fat concentration and in piglets with a higher body fat concentration compared with the starch-rich diet. This resulted in an interaction between dietary energy source and feeding level for energy balance of the sows. The energy balance of sows fed the low feeding level and of sows fed the fat-rich diet at the high feeding level were all similar, but the energy balance of sows fed the starch-rich diet at the high feeding level was less negative. These results suggest that extra fat in the diet enhances milk fat output, whereas extra starch is used for both milk production and prevention of severe body reserve losses of the sow.

    Dietary energy source, feeding level, and reproductive traits (Experiment 2)

    Whether the treatments affected plasma insulin profiles and reproductive traits during and after lactation is described in Chapter 3 and 4. Plasma insulin concentration was higher in sows fed the starch-rich diet than in sows fed the fat-rich diet during lactation. LH pulse frequency during lactation tended to be lower in sows fed the fat-rich diet compared to those fed the starch-rich diet. At the high feeding level, no effect of dietary energy source on WEI was found. However, at the low feeding level, the fat-diet resulted in a 22 h longer WEI compared with the starch-rich diet. Dietary energy source did not affect other reproductive traits.

    Feeding level did not affect plasma insulin profiles during lactation. Sows fed the high feeding level during lactation had a higher LH pulse frequency during and after lactation, a lower risk to remain anestrous after weaning, and a higher ovulation rate compared with sows fed the low feeding level. Periovulatory profiles of estradiol, LH, and progesterone hardly differed between treatments. No differences between treatments were observed for the number of embryos, uterine-, and placental development.

    Plasma insulin concentrations during lactation were never related with the determined reproductive traits. Furthermore, no relationships were found between energy- or nitrogen balance and reproductive characteristics.

    Based on the results obtained from experiment 2, it can be concluded that dietary energy source during lactation affects plasma insulin concentration but has minor effects on reproductive performance of primiparous sows. A reduction of 25% in lactational feed intake seems to have more impact on reproductive traits.

    Overall analyses, regardless of treatments, showed that the relationship between the number of LH pulses on the day of weaning and the WEI was best explained by a linear-plateau model. An increase from two to seven LH pulses per 12 h resulted in a linear decrease in WEI, whereas more than 7 pulses did not shorten the WEI further. Furthermore, it was demonstrated that the mean plasma progesterone concentration in early pregnancy was positively related with the percentage of embryo survival, especially in progressing pregnancy (from 170 h after the LH surge onwards).

    Dietary energy source and reproductive performance (Experiment 3).

    In the experiment described above (Chapter 2 to 4), sows were fed either the fat- or starch-rich diet from parturition until d 35 of subsequent pregnancy It is therefore, impossible to distinguish effects of dietary energy source fed during the lactation period, the WEI, or the early pregnancy, on reproduction. Effects found during pregnancy may be a result of changes during WEI or even lactation. Therefore, another experiment was conducted in which primiparous sows were fed either the fat- or starch-rich diet during the weaning-to-ovulation interval or during early pregnancy (until d 35). The results obtained from this experiment are described in Chapter 6. Sows fed the fat-rich diet before ovulation had a higher risk to maintain anestrous after weaning than sows fed the starch-rich diet. No effect of dietary energy source fed either before ovulation or during early pregnancy was found on uterine, placental, and embryonic traits.

    IGF-1 and reproductive performance (Experiment 2 and 3)

    Because plasma insulin concentration did not show relationships with reproductive traits (Chapter 3 and 4), additional analyses were performed to determine plasma IGF-1 (insulin-like growth factor-I) concentration during and after lactation, and its relationships with reproductive characteristics. In literature, IGF-1, together with insulin, is often posited as an intermediate between nutrition and reproduction in the pig. Results of these analyses are described in Chapter 5. Plasma IGF-1 concentration was higher in sows fed the high feeding level during lactation and also in sows fed the starch-rich diet. Furthermore, IGF-1 concentrations on d 21 of lactation and on d 22 (weaning) were positively related with the LH pulse frequency on d 22 and the height of the preovulatory LH surge. Finally, IGF-1 concentration in sows with a low body weight at farrowing and severe lactational body weight loss was decreased compared to heavier sows at farrowing or sows with less lactational body weight loss.

    Conclusions and implications

    The major question to be answered in the present study was whether dietary energy source affects plasma insulin concentrations and reproductive performance of primiparous sows. Based on the results obtained from the three experiments, it can be concluded that fat-rich diets fed during lactation depress the secretion of insulin compared to starch-rich diets. The LH secretion by the pituitary during lactation tended to be decreased in sows fed the fat-rich diet, possibly explaining the finding that the return to estrus was delayed in these sows. However, this lower LH pulsatility and delayed return to estrus were not related to plasma insulin concentration. Dietary energy source does not seem to affect reproductive traits on the uterus level.

    The second question to be answered was whether effects of dietary energy source on reproductive performance are dependent on the metabolic status of sows during lactation. In the present study, no interaction between dietary energy source and metabolic status on reproductive traits was found, even though the energy balance of the lactating sows was affected by dietary energy source.

    Based on these results, the use of fat-rich diets for primiparous sows, and probably also for multiparous sows, needs to be critically evaluated. Based on the metabolic and reproductive point of view, starch-rich diets seem to be more beneficial for sows than fat-rich diets. Effects of fat-rich diets on litter performance after weaning need to be investigated further.

    Optimising insemination strategies in pigs
    Steverink, D. - \ 1999
    Agricultural University. Promotor(en): J.P.T.M. Noordhuizen; B. Kemp; N.M. Soede. - S.l. : S.n. - ISBN 9789058080950 - 147
    zeugen - varkens - kunstmatige inseminatie - voortplanting - voortplantingsefficiëntie - bevruchting - spermatozoön - dosering - sperma - oestrus - ovulatie - tijd - wiskundige modellen - simulatiemodellen - commerciële landbouw - sows - pigs - artificial insemination - reproduction - reproductive efficiency - fertilization - spermatozoa - dosage - semen - oestrus - ovulation - time - mathematical models - simulation models - commercial farming

    INTRODUCTION

    Reproductive efficiency shows large variation between farms. The origin of the variation between farms, with respect to these reproduction results, is very complex. Factors like health status, husbandry system, management and breed can have an influence on reproduction results. One of the management factors is timing of insemination, which influences reproduction results by affecting fertilisation.

    The research described in this thesis deals with the possibility of developing a method to optimise insemination strategies for individual farms. Therefore three objectives were formulated: the first objective is increasing insight in the effects of the interval between insemination and ovulation on fertilisation results. The second objective is increasing knowledge on the possibilities of predicting the moment of ovulation of sows at a farm. The final objective is developing a method which can be used for optimising insemination strategies at commercial farms.

    FERTILISATION IN RELATION TO INSEMINATION AND OVULATION

    In Chapter 2 the sensitivity of the relation of the insemination to ovulation interval (IO) and fertilisation results is studied. Fertilisation results are not very sensitive to variation in the number of inseminated sperm cells in the range of 1 x 10 9 to 6 x 10 9 sperm cells (Chapter 2.1). Sows with more than 4 ml backflow of semen during insemination had reduced fertilisation results when the sows were inseminated with 1 x 10 9 sperm cells, but this was not seen with an insemination dosage of 3 x 10 9 or 6 x 10 9 sperm cells (Chapter 2.2). Backflow of semen after insemination did not affect fertilisation results. It could be concluded that sub-optimal circumstances like a combination of a low dosage and loss of sperm cells due to backflow during insemination, lead to sub-optimal fertilisation results.

    Fertilisation is a complex process, resulting in no, partial or complete fertilisation of the oocytes. The variation in conception (at least one oocyte fertilised) and fertilisation rate between sows is high, but a large part of the variation is related to the interval between insemination and ovulation. A mathematical model for conception and fertilisation is described in Chapter 2.3. The data used for estimating the parameters in the model were derived from multiparous sows that were inseminated once with a commercial sperm dose of 3 x 10 9 sperm cells of proven quality which was stored for less than 48 h and with sperm cells. In the model, the probability of conception is maximal (98%), when insemination is performed between 29 and 3 h before ovulation. The probability of complete fertilisation (all oocytes fertilised) is maximal when insemination was performed at 9.6 h before ovulation. At this optimal fertilisation point, the probability of partial fertilisation is 21% which increases beyond this point.

    PREDICTION OF OVULATION

    Fertilisation results are related to the interval between insemination and ovulation. Therefore, the moment of ovulation is a crucial moment for timing of insemination. Many potential ovulation predictors have been studied, but only oestrus duration is a reasonable estimate (retrospectively) for ovulation. Ovulation takes place at on average twothirds of oestrus. Unfortunately oestrus duration is very variable.

    The average oestrus duration is different between farms ranging between 31 and 64 h (Chapter 3.1). Moreover, oestrus duration is consistent from month to month within a farm with a repeatability of 86%. Furthermore, oestrus duration is negatively related to the weaning to oestrus interval. This relation differs among farms. These specific farm parameters can be used to predict the oestrus duration and from that the ovulation can be predicted. These farm parameters (average oestrus duration and the relation of weaning to oestrus interval and oestrus duration) can be used to define a specific insemination strategy for each farm.

    DEVELOPMENT OF A MODEL FOR INSEMINATION STRATEGIES

    There are a variety of factors influencing the reproduction process. The complexity of this reproduction process makes a modelling and simulation approach valuable because effects of the underlying processes can be controlled. A PIG Simulation model for Insemination strategies (PIGSIS) was developed which consists of two parts: (1) the reproduction events from the number of ovulated oocytes until the number of piglets at farrowing and (2) timing of insemination relative to ovulation based on the farm parameters (weaning to oestrus interval, oestrus duration, etc.). PIGSIS simulates the reproduction results at day 1, 5, 10, 15, 35 and 110 of pregnancy. Many physiological processes are included in PIGSIS e.g. fertilisation, embryonic mortality (degeneration, maternal recognition of pregnancy, embryonic uterine capacity) and foetal mortality (foetal uterine capacity). After verification and validation it could be concluded that PIGSIS is a robust model that reasonably simulates reproduction results. Under the basic situation (average oestrus duration of 47 h and average parity of 4.2) and when insemination was applied between 0 and 24 h before ovulation PIGSIS simulates 12.9 total born piglets and a farrowing rate of 94.9%. Under these conditions the average embryonic and foetal mortality of the conceptuses was 34.9% and 3.0%, respectively. The effect of insemination to ovulation interval on fertilisation results is clear, but the effect becomes less clear as gestation proceeds resulting in a more pronounced effect on litter size than on farrowing rate.

    In the General discussion the results of the studies are discussed and an illustration of the usability of PIGSIS is given. Verification and partial validation gave confidence in the model. However, a further validation is required to evaluate the model as a whole. Therefore PIGSIS is still in its developing stage and reservations has to be taken into account at this stage by using PIGSIS for defining optimal insemination strategies on farms

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