Lambs born to hoggets tend to be relatively lightweight at birth (Drymundsson, 1973; McMillan & McDonald, 1983) and display low survival rates to weaning (McCall & Hight 1981; McMillan & McDonald, 1983). In addition the incidence of singletons in hoggets often exceeds 92% (McCall & Hight, 1981; McMillan & McDonald, 1983). Therefore management procedures that improve both birth weight and survival of singleton lambs should have a significant effect on returns. Severe under nutrition during pregnancy of mature ewes can lead to reduced ewe and lamb performance (Rattray 1986), which can negatively affect lamb survival. However to date minimal research under New Zealand’s pastoral conditions has been undertaken in hoggets. In contrast to the mature ewe, it is also advantageous for the hogget to be increasing in conceptus-free live weight during pregnancy if lifetime performance is not to be negatively affected. Interestingly, under concentrate feeding regimes in the United Kingdom it has been reported that a high level of hogget nutrition in pregnancy, actually reduces both lamb birth weight and survival (Wallace et al., 1996). Shearing mature ewes in mid- to late-pregnancy has been shown to differentially increase singleton- (Morris et al., 2000; Kenyon et al., 2002a) and twin-lamb birth weights (Morris & McCutcheon, 1997; Morris et al., 1999; Kenyon et al., 2002b). Mid-pregnancy shearing has tended to increase twin-lamb survival rates (Morris et al., 1999; Kenyon et al., 2002b) but has been found to decrease singleton survival rates in one of four studies (Kenyon 2002). The effect of mid- to late-pregnancy shearing of hoggets has not been examined under pastoral conditions in New Zealand. Due to the low rate of twin pregnancies in hogget’s the chance of achieving a positive affect from mid-pregnancy shearing on both a lamb birth weight and survival may be low. The aims of these studies were to determine if hogget live weight change and shearing treatment during pregnancy could be used to manipulate singleton lamb birth weight and survival.
Proceedings of the New Zealand Society of Animal Production, Volume 64, Hamilton, 175-178, 2004
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