A study of two genetic methods for increasing the performance of sheep in New Zealand : crossbreeding between the Romney, Finnish Landrace and East Friesian : use of number of foetuses scanned as a selection predictor : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Animal Science at Massey University

Abstract

New Zealand's national lamb weaning percentage has been around 100% since 1960 (Walpole, 1995), and as prolificacy is a major determinant of productivity and economic efficiency in sheep production systems (Nitter, 1987 IN: Maria, 1995; Gabina, 1989), the improvement of this trait at a national level is of significant economic importance. The development of more reproductively efficient sheep can be achieved through selection within breeds, by crossbreeding, or by importing new genetic material. This study examines two ways of improving the prolificacy of sheep; by crossbreeding newly imported genetic material with the New Zealand Romney, and by altering the selection methods for prolificacy by using an alternative selection character. The Finnish Landrace and East Friesian are both prolific sheep breeds, and their introduction to New Zealand has provided a potential opportunity to increase prolificacy in New Zealand by crossbreeding them with the current New Zealand sheep population. By assessing their performances under New Zealand environmental and management practices, and in relation to and with current New Zealand sheep, their potential may be predicted. It is important to take advantage of both their additive gene effects and their non-additive genetic interactions (or heterosis) with current New Zealand breeds. The aim should be to achieve an ideal breed composition either as a new composite breed or as regularly reconstituted crossbred stock. The additive and non-additive figures can be used to predict the phenotypic performances for different breed composites by simulating the outcomes of crosses between different ram types made up of different combinations of the breeds with current New Zealand sheep.