Keywords: dairy cows; dietary energy source; glucogenic nutrients; lipogenic nutrients; negative energy balance; metabolic disorders; reproduction, immune system
Dairy cows experience a negative energy balance (NEB) in early lactation which results from high energy requirements for milk production accompanied by a limited energy intake. Nutrition has been indicated as an important factor in the incidence and severity of NEB and NEB–related metabolic and reproductive disorders, like ketosis and delayed resumption of ovarian activity. A metabolic effect of a NEB in dairy cows is suggested to be an unbalanced availability from glucogenic and lipogenic nutrients. The objective of this thesis was to study the effect of lipogenic and glucogenic diets on the energy balance (EB) and risk of metabolic and reproductive disorders in dairy cows in early lactation. The first study, a literature survey, illustrated that feeding extra glucogenic nutrients relative to lipogenic nutrients, decreased milk fat and seemed to decrease plasma non-esterified fatty acid (NEFA) and β-hydroxybutyrate (BHBA) concentrations. Since studies were scarce and mostly included a confounding effect of dietary energy source with energy intake, it was difficult to draw conclusions on the energy source effects on EB and fertility. Therefore, in the second study, 16 dairy cows were either fed a glucogenic or a lipogenic diet. Diets were isocaloric and equal in intestional digestible protein. Energy balance was determined in climate-respiration chambers from week 2 until week 9 of lactation. The glucogenic diet decreased milk fat yield and milk energy and tended to decrease body fat mobilisation compared with the lipogenic diet. The objective of the third study was to study the effect of dietary energy source on EB, metabolites and some reproduction variables. Dairy cows (n=111) were fed glucogenic, lipogenic or mixed diet from week -3 until week 9 relative to calving. Multiparous cows fed the glucogenic diet had lower milk fat yield, higher calculated EB, and lower plasma NEFA, BHBA and liver tri-acyl glyceride concentration and tended to have less days postpartum till first ovulation. Additionally, in the third study, the presence of natural antibodies (NAb) in plasma and milk of individual dairy cows was determined. Relations were detected between NAb and EB and plasma metabolites, suggesting that alterations in immune competence peripartum are reflected in the humoral part of the innate immune system.
In conclusion, increasing the glucogenic nutrient availability improved the EB and had potential to reduce the risk of metabolic disorders and to improve reproductive performance in dairy cows.