Abstract:
Proc. Aust. Soc. Anim. Prod. (1978) 12: 199 BIRTH WEIGHT AND SURVIVAL IN MERINO SHEEP IN NORTH WEST QUEENSLAND MARY ROSE* Neo-natal losses are Merino sheep in north west weights have been shown to experimental flocks (Moule survival, birth weight and a great source of reproductive wastage in Queensland (Moule 1966). Lambs with low birth have poor survival rates in both commercial and 1954, Rose 1972). Further investigations of its heritability are reported here. Mean birth weights ranged from 3.3 to 3.6 kg. for lambs born in spring (1959-64) but only 2,5 to 2.9 kg in autumn (1966-70). Over the whole period, the- mean birth weight of surviving lambs was 3.4 kg and of those which died in the first three days after birth 2.8 kg. Season of birth did not affect this differential. TABLE 1: % Lambs born and death rates () for birth weight classes About one third of all lambs below 2 kg did not survive and 30% of autumn born lambs were in this class. Only 2.6% of all lambs born in the 10 years studied weighed more than 4.5 kg and only two of these died. The average birth weight of the flock was well below optimum for survival regardless of lambing time. One possibility of improving survival may be selection for higher birth weight. However, heritability estimates calculated by dam-offspring and sire-offspring regressions were low; 0.19 + 0.05 and 0.06 f 0.05 These heritabilities indicate that maternal effects are respectively, important and it,is unlikely that selection for increased birth weight would result in a sufficient increase in birth weight to improve lamb survival. Other genetic relationships need to be investigated which may be useful in improving birth weight and survival. However, more promising avenues seem to involve manipulation of the environment to overcome the serious constraints on survival (Hopkins and Pratt 1976). HOPKINS, P.S., and 11: 153. MOULE,G.R. (1954) MOULE, G.R. (1966) a ROSE, Mary (1972). l PRATT , M.S. (1976). Proc. Aust. Soc. Anim. Prod. Aust, vet. J. 30: 153. Aust. vet. J. 42: 13, Proc. Aust. SocrAnim. Prod. 9: = 48. * Department of Primary Industries, Wool Biology Laboratory, Yeerongpilly, Q. 4105. 199.