This experiment investigated differences in birth weights and survival in lambs born to hogget and mature ewes. It included 1082 mature ewes with a scanning rate of 1.87 fetuses per ewe joined and 1026 hoggets with a scanning rate of 0.80 fetuses per hogget joined, that were bred together, and lambed separately, under commercial farming conditions. At lambing, birth weight, lamb vigour score, and ewe maternal behaviour score were recorded. Lambs born to hoggets were lighter and less vigorous than lambs born to mature ewes (P<0.05). Single-born lambs were heavier at birth (P<0.05), and had greater survival at birth (P<0.05) than did twin-born lambs. Twin-born lambs were heavier (P<0.05) at birth, and had greater survival at birth (P<0.05) than triplets. There was an interaction of dam age and birth rank on lamb survival to weaning (P<0.01). At all birth ranks lambs born to hoggets had lower survival to weaning than lambs born to mature ewes, and the difference in survival increased with increasing birth rank. Lambs that had a vigour score of 1 had lower survival (83.5%; P<0.05) than lambs that had a vigour score of either 2 or 3 (88.6- and 91.4%, respectively). Maternal behaviour score did not affect lamb survival (P>0.05). Lambs born to hoggets are at greater risk of mortality, so farmers need to prioritise their time and resources towards hoggets at lambing time.
Proceedings of the New Zealand Society of Animal Production, Volume 78, Rotorua, 16-20, 2018
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