High cost of milk proteins has driven development of cheaper whey-based milk replacer (WBMR) as an alternative to skim-milk (casein)-based milk-replacer (CBMR) for artificial-rearing of young ruminants. This study compared growth, antibiotic/anti-inflammatory use and mortality in lambs reared on either WBMR (n=138) or CBMR (n=151) in the first three weeks of rearing at commercial scale. There was a diet x rank interaction (P=0.001) whereby CBMR-fed single/twin and triplet/quad lambs had the highest average daily gain (ADG) independent of birth-rank (362 vs. 358 g/d respectively, SED=16.7) compared to WBMR-fed lambs where higher ADG was observed in triplet/quad compared to single/twin lambs (275 vs. 213 g/d respectively, SED=16.7). Males tended to have higher ADG than females (311 vs. 294, SED=9.7 g/d, P=0.064). Overall, there was a tendency for greater mortality (11% vs. 4%; P=0.055), and overall incidence rate (N/100 animal weeks) for use of antibiotics (4.43 vs. 1.27; P=0.073) and anti-inflammatories (4.59 vs. 1.59; P=0.099) in WBMR- than CBMR-fed lambs. These results highlight that CBMR under an ad-libitum milk-feeding regime supports greater ADG independent of birth-rank and reduces the incidence of disease in the first three weeks of life compared to WBMR. Furthermore, WBMR under an ad-libitum milk-feeding regime results in lower ADG of single/twin-born lambs compared to their triplet/quad counterparts. Keywords: lambs; artificial rearing; milk replacer; composition; growth; health; mortality
New Zealand Journal of Animal Science and Production, Volume 81, Online, 22-28, 2021
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