This trial was designed to determine if ewes with triplets produce more milk than those with twins, and, if not, do triplet lambs compensate by extra grazing. Milk yield (MY) of ewes with twin (n=13) and triplet (n=8) lambs, grazing pasture in spring was measured four, seven and ten weeks postpartum. Ewes and lambs were separated in the morning and MY was measured by the oxytocin method. MY did not differ in ewes with triplets (2525 ± 243 g/d) from that in ewes with twins (2204 ± 149 g/d) at week four, week seven (1847 ± 238 versus 1684 ± 111 g/d), or at week ten (1448 ± 139 versus 1264 ± 85 g/d). NIRS analyses showed no significant consistent difference in fat (triplet: twin 7.7: 7.5 ± 0.4%), protein (4.4: 4.3 ± 0.2%), lactose (4.71: 4.72 ± 0.03%) and total solids (17.48: 17.36 ± 0.35%) composition of milk from ewes with triplet or twin lambs (data are means of all samples). Mammary gland dimension B, the distance across the gland next to the teats, was better correlated (R2 0.31, P<0.05) with MY than other dimensions tested. Behaviour observations (whether the lamb was grazing or suckling) were made weekly 3-9 weeks postpartum. The time spent grazing by triplets (39.4 ± 1.94 % on lactation day 29) was significantly greater (P<0.05) than the time spent grazing by twins (37.7 ± 1.94% on lactation day 29) on three observation days and, overall, triplet lambs spent more time grazing than twin lambs. Birth weight of twin lambs (4.39 ± 0.14 kg) was not significantly greater than that of triplets (4.00 ± 0.20 kg), but they grew significantly faster (P<0.05) from week four till week ten, gaining 17.0 kg compared to 14.9 kg for triplets. Triplets suffer a relative lack of available milk nutrients compared to twins and are not able to completely compensate for this by increasing grazing time.
Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 444-449, 2006
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