Abstract

Several breeding technologies are available to sheep breeders for increasing the rate of genetic progress in their flocks. The relative merits of these technologies depends on the selection objective and other breeding and management circumstances. This paper investigates the effects of artificial insemination (AI), progeny testing and an open-nucleus flock, on a breeding programme for fine woolled merinos. The selection objective was to decrease Mean Fibre Diameter (MFD) while maintaining Clean Fleeceweight (CFW). Two population structures were considered: a)Maintaining a closed nucleus flock of 1000 breeding ewes b)Operating an open-nucleus breeding scheme sourcing a proportion of replacements from the progeny of 5000 contributing ewes. For each structure, the benefits of AI and progeny testing were investigated individually and in combination. For the range of options considered, selection resulted in a reduction of one micron in MFD every three to five years, with no reduction in CFW. All other things equal progeny testing decreased the genetic progress possible by 0.04-0.06 u/year. An open-nucleus breeding scheme increased the rate of genetic gain by 0.06 u/year with progeny testing or 0.03 u/year in the absence of progeny testing. AI increased genetic progress by 0.06 u/year. The combination of AI and an open nucleus provided the maximum potential rate of genetic gain (0.36 u/year). To optimise the age structure for this combination of breeding technologies, the nucleus flock comprised 60% two-tooth ewes. These results describe the impact of breeding technologies on the rate of genetic gain. To determine their cost-effectiveness, the marginal genetic gain provided by any individual technology must be weighed up against the costs and management constraints that the technology imposes.

RG, Sherlock, and DJ Garrick

Proceedings of the New Zealand Society of Animal Production, Volume 55, , 278-280, 1995