Effects of body fatness at lambing and diet in lactation on body tissue loss, feed intake and milk yield of ewes in early lactation

Abstract

SUMMARYThirty-six mature Finnish Landrace × Dorset Horn ewes, each suckling two lambs, were used in a comparative slaughter experiment to measure changes in body tissues during early lactation. Two levels of body fatness at lambing were established by giving ewes a complete diet containing 10 MJ metabolizable energy (ME) and 139 g crude protein (CP)/kg d.m. either close to requirements or ad libitum during the second half of pregnancy. In lactation half the ewes in each group were given a complete diet containing either 90 (diet A) or 60 (diet B) % milled hay ad libitum. These diets contained 7·9 and 9·2 MJ ME and 121 and 132 g CP/kg d.m. respectively.Ewes fed at the two levels in pregnancy contained 8·4 and 19·6 kg chemically determined fat 5 days after lambing but had similar amounts of body protein, ash and water. Over 6 weeks of lactation ewes given diet A lost 60 and 69% of these weights of fat respectively, while ewes given diet B gained 5% and lost 30% respectively. Up to 26 g of body protein was lost daily from ewes given diet A but none from ewes on diet B. During early lactation the weight of the empty digestive tract increased while the weights of most other body components, particularly the carcass, decreased. The ratio of body energy change to live-weight change varied from 24 to 90 MJ/kg. Thus live-weight change did not accurately reflect relative or absolute changes in body energy.Voluntary food intake was greater for ewes given the high-energy diet (B) than for those given diet A and was depressed in the fatter ewes. Differences in intake could be explained by the effects of body fatness and diet on the weight of gut contents. Milk yield was not significantly affected by body fat reserves but was higher on diet B than A. Fat content of milk was higher and protein content lower for ewes with the higher fat reserves at lambing.As the contribution of fat loss to energy available for milk synthesis increased there appeared to be a reduction in the energetic efficiency of milk synthesis. A number of possible reasons for this are discussed.

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

“…During that period L-BCS ewes produced more milk with higher fat concentration but lower protein concentration compared to H-BCS ewes. These data are in contrast to previous observations in early lactating ewes where milk yield was not affected by BCS, whereas milk fat concentration was higher and protein concentration lower for ewes with higher fat reserves (Cowan et al, 1980). In our experiment, the initial differences in milk yield between the two BCS groups supported the use of the covariate analyses to compare the influence of treatments over these productive parameters throughout the trial.…”

“…Some studies have focused on the effects of underfeeding on sheep performance in perinatal (Lawlor and Hopkin, 1981) and early lactation periods (Cowan et al, 1980;Agus and Bocquier, 1995) in which the mobilization of body reserves is supported by the specific metabolic and physiological status of the animal (Blanc et al, 2006). The consequent negative energy balance generally results in a decrease in milk yield and protein concentration, and in an increase in milk fat (Bocquier and Caja, 2001).…”

Leptin secretion and hypothalamic neuropeptide and receptor gene expression in sheep

“…Food intake increases after birth, reaching a plateau between 2 and 3 wk postpartum (24,60). Nevertheless, ewes suckling two or more lambs lose ϳ5 kg in body weight, mostly because of loss of fat from adipose tissue during the first 5-6 wk of lactation (22,23,24,60). Ewes suckling a single lamb do not appear to lose adipose tissue lipid, whereas ewes suckling three lambs lose an amount of adipose tissue lipid similar to those suckling two lambs (66).…”

Adipose tissue metabolism and its role in adaptations to undernutrition in ruminants

“…When the undernutrition is moderate, however, initial body fatness has only a limited influence on fat mobilization (Cowan et al 1982). Hence, in contrast to dry ewes (Panaretto, 1964), lactating ewes are able to mobilize a large amount of body lipids without health problems (Cowan et al 1980). This difference between lactating and dry animals in managing an intense body lipid mobilization is probably related to the large mammary drain of non-esterified fatty acids (NEFA; see p. 130).…”