Artificial rearing with milk replacers of varying fat and total solids compared with natural suckling: Pre- and post-weaning performance of lambs

This study evaluated the effects of increasing total solids (TS) and fat concentration in milk replacer (MR) on the performance of artificially reared lambs compared with naturally suckled lambs. Forty-eight 3-day-old Shal lambs were assigned to natural suckling (EWE; 6.37% fat, 17.4% TS) or one of three MR treatments: low-fat-low-solids (LF-LS; 3.56% fat, 16.3% TS), low-fat-high-solids (LF-HS; 4.27% fat, 19.6% TS), or high-fat-high-solids (HF-HS; 4.95% fat, 19.6% TS). Increasing TS raised the milk protein concentration to a level comparable to that of ewe milk (4.8%), while partial replacement of lactose with fat reduced osmolality in HF-HS relative to LF-HS (466 vs. 506 mOsm/kg). Lambs were fed milk until day 62 and monitored until day 103. Lambs fed LF-HS and HF-HS consumed more protein and metabolizable energy than those fed LF-LS, resulting in improved pre- and postweaning average daily gain and skeletal growth. Furthermore, LF-LS lambs exhibited lower serum cholesterol, a tendency toward lower glucose, and higher β-hydroxybutyrate concentrations at weaning, indicating a less favorable energy status. Although HF-HS increased nutrient intake and hip width compared with LF-HS, both high-solids formulations achieved growth comparable to that of EWE. Nutrient digestibility, diarrhea days, and serum concentrations of insulin, cortisol, and thyroxine were unaffected, whereas serum total protein was greater in EWE than in the MR groups. Despite the associated increase in osmolality, increasing MR solids from 16.3% to 19.6%, particularly in HF-HS, improved nutrient intake and supported growth comparable to natural suckling without adversely affecting the assessed health indicators.