THE USE OF DIETARY FATS AND CONCENTRATES TO ALLEVIATE THE NEGATIVE ENERGY BALANCE IN CROSSBRED COWS IN EARLY LACTATION

Energy balance (EB) is defined as the difference between energy intake and energy expenditure. Fertility in the high-merit cow has been adversely associated with high milk production, low intake of energy and mobilisation of body reserves in early lactation, which combine in the term negative energy balance (NEB).  The timing of insemination usually coincides with peak milk yield, when dairy cows are often in NEB. Crossbred cows (Bos taurus x Bos indicus) in the tropics have comparatively lower nutrient requirements and different partition of nutrients than high merit dairy cows. Thus, it would be expected that both the magnitude and length of negative energy balance were different in a crossbred cow. Because of marked differences compared with high-merit cows, crossbred cows in the tropics would be expected to show greater response to additional energy in early lactation improving their energy status and hence reproductive performance. Knowing the influence of nutrition on reproduction, many methods have been proposed for manipulating the diet to avoid or to alleviate negative energy balance. The use of fats is one alternative, which has been extensively studied in dairy and beef cows but with inconclusive results. Another alternative is to use starch-based concentrates, taking into account level of inclusion and quality and availability of pasture, in order to avoid substitution effects and to get maximum profits. Two experiments were carried out in Yucatan Mexico, in order to evaluate the use of bypass fats (calcium soaps of long-chain fatty acids, CAFA) or a starch-based concentrate to alleviate the NEB in grazing crossbred cows in early lactation. The NEB in early lactation was successfully avoided by the use of the starch-based concentrate but not by the use of bypass fats, this due to a reduction in the grass DM intake. It was concluded that crossbred cows in the tropics may experience a period of NEB postpartum, which can be avoided if they are supplemented with starch-based concentrates but not with bypass fats.