Factors affecting age at first lambing in Yankasa ewes

Data on 133 primiparous Yankasa ewes covering a period of 8 years (1983-1991) were analysed by least squares method for the effects of season, year, litter size, birth weight, weaning age and weaning weight on age at first lambing (AFL). Results showed the AFL (+/-SE) to be 533.1 +/- 10.3 days. Only the effect of season on AFL was significant (P < 0.01) while year of lambing, birth weight, litter size, weaning age and weaning weight did not affect AFL significantly (P > 0.01). AFL was 476.9 +/- 23.3, 523.9 +/- 19.2, 549.8 +/- 19.7 and 581.9 +/- 19.5 days for late wet, early dry, late dry and early wet season born ewes respectively. AFL was significantly (P < 0.01) lowest for ewes born in the late wet season and highest for ewes born in the early wet season. There was no significant (P > 0.01) difference in AFL between ewes born in the early dry season and ewes born in the late dry season, and between late dry and early wet season born ewes. (C) 1997 Elsevier Science B.V.