Effect of weaning system on lamb growth, mammary gland development and ewe milk production in dairy sheep managed in an outdoor pasture-based commercial farming system

Abstract

Background: In contrast to global dairy sheep production systems, sheep milking is an emerging industry in New Zealand. For some producers, natural rearing of the lamb is a requirement to meet market expectations, while for others it is a lower-cost farm system option. The objective was to merge science and practice to determine the feasibility of a mixed suckling and milking system compared to a traditional exclusive suckling management system on growth performance of the progeny and dam milk production in an outdoor pasture-based dairy sheep farming system at commercial scale.   Approach: At 14 days postpartum, twin- and triplet-bearing mixed-age East Friesian ewes were randomly allocated to either a mixed system of once-a-day milking, suckling and early weaning (MS, n=61) or control with exclusive suckling and later weaning (Ctrl, n=57) using a randomized block design. Lamb pre- and post-weaning growth rates to 4 months of age and ewe milk yield and composition during lactation were evaluated. Ewe lamb mammary gland size at 4 months of age and ewe cisternal capacity in late lactation was measured using ultrasonography.    Results: MS lambs had lower live weight at weaning (14.6 vs. 16.7 kg, P<0.001) but post-weaning average daily gain and mammary gland mass did not differ between groups. Ewe lamb mammary mass was positively associated with post-weaning but not pre-weaning live weight gain (P<0.01). Ewe milk yield and composition post-weaning was not affected by the rearing system. Ewe cisternal capacity was positively associated with milk yield but was not affected by the rearing method.   Conclusions: This study highlights that the MS compared to Ctrl system had no short- or long-term negative effects on lamb growth, health, weaning age and post-weaning mammary development compared to lambs exclusively suckled prior to weaning.   Practical implications of conclusions: This study highlights that a mixed system of suckling and once-a-day milking from 14 days postpartum has no short- or long-term negative effects on lamb growth, health, weaning age and post-weaning mammary development compared to lambs exclusively suckled prior to weaning. No post-weaning impacts on dam milk yield and composition were observed but the mixed suckling and milking system supported increased capture of commercial milk in early lactation. Ultrasonography was also employed successfully as a non-invasive tool to evaluate mammary gland development in lambs at 4 months of age and cisternal capacity and milkability of ewes in late lactation.