Abstract

The MAFTech Sire Referencing Scheme is a national programme to evaluate rams, via progeny testing, throughout New Zealand. Phenotypic effects are reduced by using "Link sires" to make comparisons between properties valid. To enable link sires to be used over large numbers of animals in diverse locations, extensive use is made of Artificial Insemination (AI). Data from over 3,000 ewes mated by AI during the 1989 breeding season are presented. Various factors and their interactions were examined by fitting a generalised linear model with binomial distribution. The model showed that: the non-return rate from cervical insemination with chilled semen was 61% for ewes which had been treated with CIDRs and 62% (SED 3.4) for naturally cycling ewes; for frozen/thawed semen inseminate by the intrauterine route the corresponding rates were 70% and 40% (SED 7.0). In ewes treated with CIDRs the non-return rate was lower for cervical compared to intrauterine in semination (61% vs 70% SED 4.0). Ewes which were in oestrus more than 24 hours before insemination had a non-return rate of 58% compared to 63% (SED 2.6) for ewes which were in oestrus between 24 and 17 hours before AI and 71% (SED 3.1) when oestrus occurred less than 17 hours before AI. There was no evidence of an interaction between inseminated increased. (Coefficient for logit regression 0.14 se 0.064). Technicians success rate ranged from 51% to 76% non returns, when adjusted for other factors. Although differences among the 31 sires did not contribute significantly to this model, predicted non-return rates when sire was added to the model ranged from 39% to 86%. There was no evidence that ewe breed influenced non-return rate.

LK, Wiggins

Proceedings of the New Zealand Society of Animal Production, Volume 50, , 387-392, 1990