Abstract

A total of 134 ewe lambs born in 1991 from the Ruakura "Kamo" out- of-season breeding flock were run with harnessed vasectomised rams from weaning and inspected weekly for onset of puberty and subsequent oestrus activity. The breeding values for date of lambing (BV) for these animals were calculated from a pedigree and performance database. Multiple regression analysis were performed to determine the value of factors associated with hogget oestrus for predicting BV. While all the factors analysed, date of puberty, age and weight at puberty and number of subsequent oestrus cycles, had significant effects, none were as useful a predictor as date of birth(Bday). Season of birth (autumn vs spring) also exerted considerable influence on date of first tup and number of cycles. The results indicate that the best method of selection at present is that based on date of birth. Further research is needed to understand the interaction between season of birth and BV as they influence the onset of puberty.

GF, Wilson, GA Lynch, and C Van Der Wel

Proceedings of the New Zealand Society of Animal Production, Volume 53, , 247-250, 1993