Effect of late lactation nutrition on milk production and composition in prolific sheep on an accelerated lambing system

Abstract Late lactation nutrition is important in prolific sheep to ensure adequate lamb growth and in the context of accelerated production, to potentially improve reproductive outcomes. Therefore, the effect of plane of energy nutrition was evaluated in 24 (Dorset x Polypay) multiparous ewes randomly assigned to diets providing either 100% (C), 70% (Low) or 150% (High) of NRC energy requirements during the last 28 days of lactation (n = 4 single- and n = 4 twin-rearing ewes/group). Milk volume (MILK) was measured by hand milking following oxytocin treatment (20 I.U.) prior to and after 3 hours of removal from lambs with samples taken for composition analysis just prior and after 2 and 4 weeks of treatment. Body weight (BW) and body condition score (BCS) were followed throughout. A mixed statistical model accounting for rearing status and stage of lactation revealed that High ewes gained 4.0kg and 0.28BCS units and Low ewes lost 4.9kg and 0.21BCS units (P < 0.05, High vs. Low for both), but these outcomes did not differ by rearing status. C ewes maintained BCS, but lost 3.7kg relative to High ewes (P < 0.05). Ewes rearing twins produced greater MILK than singles (1.85L for singles vs. 2.32L for twins, P < 0.01). However, MILK in C ewes remained unchanged regardless of rearing status over the study period. MILK response to treatment differed according to rearing status (P < 0.01) with twin but not single-rearing ewes responding. After two weeks, twin-rearing High ewes increased MILK ~50% relative to pre-treatment measures (P < 0.01) and remained elevated until week 4, while C or Low ewes showed no treatment response. Milk fat percent increased over lactation in all ewes (P < 0.01). These data indicate that only twin-rearing ewes were able to respond in milk synthesis to increased energy intake demonstrating that current feeding standards for twin-rearing ewes limit milk production.