Abstract:
Proc. Aust. Soc. Anim. Prod. (1974) 10; 285 FACTORS AFFECTING PUBERTY IN MERINO EWES H. HAWKER* and J.P. KENNEDY* The age at which puberty (first oestrus) occurs in the ewe determines the age at which breeding is first possible, and so may influence lifetime lamb production. Other studies (Watson and Gamble 1961, Murray 1972) have indicated that both season of birth and nutrition influence the age at puberty in the Merino. At Fowlers Gap Research Station, near Broken Hill, New South Wales, age and live weight at puberty are being investigated in South Australian type Merino ewes born at five different times of the year. Individual birth dates of ewes are not available. Ages are calculated from the mean of the lambing distribution. Ewes are run continuously with active harnessed vasectomized rams from weaning (3.5-5 months of age) until ten weeks prior to first joining. Weekly raddle checks and five weekly weighings are made, from which approximate age and live weight at puberty may be determined. All live weights are corrected for wool growth. Table 1 shows progress results from the experiment. TABLE1 Age and live weight of ewes at puberty in relation to time of birth Watson and Gamble (1961) have reported a strong season of birth effect on age at first oestrus in Merino ewes on improved pasture in temperate Victoria. They found that ewes born in spring, winter and summer reached puberty at 186, 286 and 375 days respectively, with corresponding live weights In semi-arid northwest Queensland, Murray (1972) found of 34, 37 and 43 kg. puberty in autumn and spring-born Merino ewes grazing natural-pasture so occur at 537 and 580 days and live weights of 33.2 and 33.7 kg respectively. The ages at puberty shown in Table 1 are somewhere between extremes recorded in Victoria and northwest Queensland, reflecting environmental differences. In both this study and that of Murray (1972) seasonal variations in available nutrition appear to have dampened'the strong season of birth effect that appeared in Victoria under conditions of near optimal nutrition. Extension of the study over several years will help in assessing the relative importance of those factors that determine initiation of breeding activity in ewes. REFERENCES MURRAY, R.M. (1972). Proc. Aust. Soc. Anim. Prod. 2: 181. Aust. J. agric. Res. 2: 124. WATSON, R.H., and GAMBLE, L.C. (1961). * School of Wool & Pastoral Sciences, University of N.S.W., Kensington, N.S.W. 285