Comparison of milk replacer composition and effects on growth and health of preruminant lambs, and health-associated costs of artificial rearing

Abstract

This research evaluated the effects of 2 milk replacer (MR) formulations on lamb performance, morbidity, mortality, and antibiotic usage and health-associated costs of artificial lamb rearing. East-Friesian male lambs (n = 206; BW = 4.9 ± 0.24 kg; 2–5 d of age) were stratified by BW and age and randomly allocated to 1 of 8 pens per treatment (10–15 lambs/pen). Lambs were artificially reared on 1 of 2 commercially available MR formulations [MR1 (100% milk protein): 25.3% protein, 26.5% milk fat, 34.9% lactose; MR2 (milk protein + hydrolyzed wheat protein): 23% protein, 24.3% vegetable oil, 30.4% lactose]. The MR was offered ad libitum via automatic feeders, mixed on-demand at 230 g/L of MR at 37°C. Lambs had free access to grass hay throughout the study. Lamb BW was recorded on entry and weekly thereafter to determine ADG and the time taken to reach a minimum of 13.5 kg of BW. Individual animal health assessments were undertaken daily for the first 4 d and weekly thereafter, and any animal health issues were recorded. All animal health interventions including antibiotic use, mortality, and labor requirements for animal health and hygiene management were recorded. Lamb mortality was similar between MR1 and MR2 lambs (8 vs. 10%, P = 0.79). Overall, ADG was greater for MR1 than MR2 (mean ± SE: 296 ± 17.6 vs. 242 ± 17.7 g/d, P = 0.02). For lambs not treated with antibiotics, ADG was greater in MR1 versus MR2 lambs (331 ± 12.3 vs. 305 ± 13.5 g/d, P = 0.03) resulting in fewer days to reach a minimum of 13.5 kg of BW (target for weaning: 30 ± 1.3 vs. 33 ± 1.4 d, P = 0.03). Thus, the percentage of lambs that reached 13.5 kg without antibiotic treatment was greater in MR1 than in MR2 lambs (73 ± 4.4 vs. 48 ± 4.9%, P < 0.001). Overall, 4 times more lambs failed to reach 13.5 kg by the end of the study in MR2 than in MR1 (16 vs. 4%, P = 0.009) reflecting their 53 g/d lower ADG. A much lower incidence (range from 1.5 to 13 times) of animal health issues and associated antibiotic use was observed with MR1 compared with MR2 lambs. As a result, the costs associated with animal health interventions were greater for MR2 than for MR1 ($NZ17.2 vs. $NZ7.32 per head). Milk replacer formulation did not affect mortality rates; however, ADG was greater and morbidity, antibiotic use, and costs of animal health interventions were lower in lambs reared on a MR formulated from 100% milk proteins and fats compared with MR containing a combination of milk protein, hydrolyzed wheat protein, and vegetable oil.