Abstract

Milk yield (MY) of groups of Romney ewes lambing at 3 times of the year: January (n=9), March (n=14) and June (n=13)) was measured on alternate days in the first week postpartum and at weekly intervals for nine weeks. Twin-bearing ewes produced significantly more milk than single-bearing ewes during the first week and during the whole of lactation (63 days) (P<0.05), except in the January-lambing group, in which ewes with single lambs produced more milk then those with twins during the first week. The shape of the lactation curve for ewes with singles or twins differed significantly (P<0.01) between lambing groups, reflecting that single- and twin-bearing ewes responded differently in January, but the number of twinbearing ewes was small (n=4) in that month. MY differed significantly (P<0.01) among groups lambing in January (single MY ± SEM: twins MY ± SEM) (1605 ± 57: 1402 ± 71 g/d), March (1425 ± 38; 1802 ± 46) and June (1520 ± 43: 1951 ± 54). Despite having the lowest (P<0.05) mean pre-lambing live weight (62 ± 3 kg), ewes lambing in June produced the highest overall mean MY (1735 ± 48 g/d), whilst ewes lambing in March and January had mean pre-weaning live weights of 70 ± 2 kg (in both groups) and produced 1613 ± 42 g/d and 1504 ± 64 g/d respectively. The June–lambing ewes gained weight (1.38 ± 1.19 kg) and condition score (0.39 ± 0.16 /d) whilst weight loss was significant (P<0.05) in the March (-9.82 ± 1.15 kg) and January (-7.78 ± 1.44 kg) groups between pre-lambing and weaning, as was change in condition score (March: -0.49 ± 0.16; January: -0.63 ± 0.19). Lamb birth weights did not differ between seasons but ADG (g/d ± SEM) was highest (P<0.01) in June (0.262 ± 0.008), followed by March (0.238 ± 0.008) and January (0.202 ± 0.009).

SW, Peterson, PCH Morel, PR Kenyon, and ST Morris

Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 450-455, 2006