A note on the effects of body fatness and level of food intake on the rate of fat loss in lactating ewes

Abstract

Data from three comparative slaughter experiments involving a total of 73 ewes were used to study the influence of body fat content at the start of lactation (X1 kg) and of metabolizable energy intake (X2, MJ/day), on the rate of loss of body fat by lactating ewes over the first 6 weeks of lactation (Y, g/day). The relationship was described by the equation:Thus the rate of fat loss was greater for ewes with higher initial fat contents, but the differential became less as metabolizable energy intake increased. Since increases in body fatness depress food intake it was not possible to prevent loss of body fat during early lactation in fat ewes given high concentrate diets ad libitum. The likely response in milk yield to increase in body fatness at parturition is therefore strongly dependent on the relative levels of body fatness and metabolizable energy intake. The value of any improvement in condition of the ewe at parturition may be considerable when metabolizable energy intake during lactation is low but much less when it is expected to be high.

Reviews of the progress of Dairy Science: Long term effects of plane of nutrition on the performance of the dairy cow

“…The benefit from improved body condition at calving was less than that from additional feeding in early lactation. The trial indicates a broadly additive effect of pre and post calving feeding whereas in sheep Cowan et al (1982) indicated an interactive effect. In neither trial was feeding made proportional to yield/animal.…”

“…Cowan (1982) has brought many of the new ideas together in a valuable hypothesis on the interaction of the component parts, and discussion of the problem can be conveniently centred on his analysis. Cowan (1982) argues first, using evidence on sheep (Cowan et al 1982) that the cow underfed in lactation will draw more heavily on body fat in early lactation, and will show therefore a greater response to additional fat laid down in late pregnancy. This relationship, he reasons secondly, will be offset by the greater intake capacity of the thin cow compared with the fat cow, i.e.…”

Effects of short-term feed restriction on milk yield and composition, and hormone and metabolite profiles in mid-lactation Sarda dairy sheep with different body condition score

“…Under severe undernutrition, the level of body fat mobilization was higher in ewes that were initially fatter. However, under moderate undernutrition, initial body fatness had only a limited influence on fat mobilization (Cowan et al, 1982).…”

“…Body fat mobilization during undernutrition varies according to the duration and level of feed restriction, and initial body fatness of the animals (Cowan et al, 1982;Chilliard et al, 2000). Under severe undernutrition, the level of body fat mobilization was higher in ewes that were initially fatter.…”

The effect of level of feeding on the response of lactating ewes to dietary supplements of fish meal

“…above maintenance) together with estimates of the contribution made to energy needs by energy from body fat are also given in Figure 3. The latter estimates were made using the relationship: Y = (51 -1-7X0*, + 19 obtained by Cowan, Robinson and McDonald (1982) from a series of comparative slaughter experiments on lactating ewes given diets similar to those used in the present experiment. In this relationship Y = rate of loss of body fat (g/day), X, = amount of fat in the body at the start of lactation (kg) and X 2 -ME intake (MJ/day).…”