The export of about 2600 Friesian heifers to Kenya between 1971-1973 provided an opportunity of studying the adaptation problems experienced by these heifers. Within the framework of the NUFFIC (Netherlands Universities Foundation for International Cooperation) a research project entitled 'Adaptation of Dutch Friesian heifers in the Tropics, with special reference to Kenya' was initiated. This project studied aspects such as health parameters, reproduction and growth in the imported Friesians. Under the aegis of the project we studied the changes in cattle hair coat characteristics. This topic was chosen for 3 main reasons:
- The characteristics and the cyclic changes of the hair coat are important in the ecology of cattle.
- Various authors have drawn attention to the importance of hair coat type as an indicator of the ability of beef cattle to adapt to tropical climates.
- There were no data on adaptation problems, with regard to hair coats, of dairy cattle.
To complement the Kenyan data, I studied hair coat characteristics in Friesian heifers in the Netherlands. By thoroughly reviewing existing literature on hair follicles, sweat glands and hair coat characteristics in cattle, I obtained data that could be compared with the data I collected in Kenya and the Netherlands.
The literature review (Chapter 2.) comprises a résumé of the anatomy and physiology of the hair follicle and sweat gland (section 2.1.4.); a summary of hair follicle and sweat gland characteristics (section 2.2.12.), and hair coat characteristics of cattle (section 2.3.13.); a summary of coat shedding, the effects of photoperiod, temperature and nutrition (section 2.4.4.); and the major conclusions on how hair follicle, sweat gland and hair coat characteristics relate to heat exchange, performance and adaptation (section 2.5.5.).
Chapter 3 describes the experiments. The methods of measuring hair coat characteristics are given in paragraph 3.1. The hair samples were measured for medullation, hair diameter, hair length, melanin content, hair density and percentage of anagen hair roots. Our methods were generally the same as those reported in the literature, except for those we used to measure medullation and hair diameter.
The results of the research on hair coat characteristics of Friesian heifers in the Netherlands are described in 3.2. In this investigation 30 heifers were sampled at regular intervals. Supplementary observations on shedding of the coat were made on 6 heifers. We found that:
- In the same animal white hair samples were more medullated than black hair samples.
- The changes in various hair coat characteristics did not run parallel in all body regions. In summer the coats were uniform over the body. In autumn and winter, however, various hair coat characteristics varied significantly between body regions.
- All the characteristics considered changed with time. Large seasonal changes were found in percentage of medullated hairs, hair length and melanin content. The seasonal cycle in percentage of medullated hairs - from 50% in winter to 90% in summer -, which represents the seasonal variation in coat composition, was closely related to change in daylength.
- Large changes in coat composition occurred in spring and in autumn. In the heifers used in the shedding experiment in autumn about 50% of the hairs were shed and the increase in hair length resulted from the growth of the 'summer' hairs.
- The melanin content was found to be related to body weight gain.
The hair coat characteristics of Friesian heifers after introduction into Kenya are described in paragraph 3.3. In a preliminary study we made measurements on 25 heifers brought to Kitale in October 1972. The main study was made on 27 heifers brought to Kitale in October 1973. The most important results were:
- The percentage of medullated hairs remained at the same low level (40-50%) during the first 12 months; only after this period it increased gradually.
A few months after arrival in Kenya the percentage of fragmentary medullated hairs rose rapidly.
- It was striking that most animals grew very dense coats in the first six months in Kenya.
- Both hair diameter and hair length decreased in the first 6 months in Kenya.
- Only in those periods when the heifers experienced a rather low plane of nutrition did some hair coat characteristics correlate with body weight gain. Chapter 4 discusses some results from the experimental heifers in the Netherlands and from the heifers examined in Kenya, and presents our conclusions.
The main outcomes were:
- Contrary to the practice, in comparative studies black and white hairs should be studied separately. Moreover the body region chosen for sampling may significantly affect the results.
- The experimental heifers in the Netherlands adapted to the summer conditions by developing a short, medullated, and less dense hair coat. The seasonal rhythm in coat composition is probably due to changes in photoperiod acting through the endocrine system.
- Our results on coat shedding do not agree with those from Australia mentioned in the literature. The sequence of events in temperate zones is probably:
a. in spring most of the hairs are replaced: the non-medullated hairs disappear almost entirely from the coat and almost all the new hairs are medullated;
b. in autumn about 50% of the hairs are replaced: non-medullated hairs appear in the coat again, the hair density increases, and the 'summer' hairs increase markedly in length;
c. some replacement occurs continuously throughout the year.
- In Kenya the equatorial photoperiod probably upsets this cycle in the imported heifers. The low level of medullated hairs during the first 12 months, the marked increase in fragmentary medullated hairs, and the high hair densities in the first 6 months (mainly due to the fact that the non-medullated hairs were shed only very gradually) show that these animals had difficulties in acclimatizing. It took about 18 months before the coat composition of the heifers transferred to Kenya was about the same as that of the heifers in the Netherlands in summer. These results endorse YEATES'S (1958) view that the equatorial light environment must be regarded as an extra setback to the successful adaptation of European cattle to hot equatorial regions.
- Contrary to the assumptions in the literature that both hair follicle and hair density decrease as the animal grows and that hair density is not subject to seasonal changes, our findings suggest that a number of follicles producing non- medullated hairs remain empty in the summer months and that the number of empty follicles per unit area is inversely proportional to the number of non- medullated hairs per unit area. This would partly explain the surprizing high hair densities in the first 6 months in Kenya, because in the heifers in Kenya dense hair coats tended to be composed of more non-medullated hairs. We have indications that in animals with extremely high hair densities a number of follicles contain two hairs. So hair follicle population figures are not equivalent to hair population figures.
- Ambient temperature is related to hair length. The influence of temperature may be mediated by the thyroid.
- Plane of nutrition is probably (like in sheep and men) directly related to hair diameter.
- There was no evidence for a strong link between body weight gain and hair coat characteristics. In the Netherlands body weight gain was related to melanin content only; the significance of this relationship is not fully clear. The results in Kenya confirm the assumption of various workers that a medullated coat indicates capacity to react favourably under stressful conditions.
- In the mild climatic conditions of Kitale the hair coat is probably not very important in relation to the thermal balance of the animal. In hot-dry and hot-wet climates heat problems may arise (at least in the first year after exportation) in animals that are transferred from the temperate to equatorial regions . This has to be investigated further.
- Further research is also necessary to reveal the role of various hair coat characteristics on heat transfer. And it will be interesting to investigate the physiological mechanisms underlying the relationships between coat type and thrift in a tropical environment. This should be determined with animals kept under controlled conditions.