Genetic progress in a Romney Group Breeding Scheme

C.A. Morris, N.C. Amyes, S.M. Hickey and D.B. Binnie

AgResearch, Ruakura Agricultural Research Centre, Private Bag 3123, Hamilton, New Zealand

E-Mail:morrisc@agresearch.cri.nz

Proceedings of the New Zealand Society of Animal Production. 1999, 59: 117-120

The Auckland Romney Development Group was established in 1968 and its aims continue to be to test and select rams for Group Members, and to breed rams for sale under conditions relevant to farming in the greater Auckland district. Breeding objectives include increased litter size (NLB), weaning weight (WWT), yearling live weight (YLW), yearling greasy fleece weight (YFW), and also increased facial eczema (FE) tolerance. Each year until 1993, members received selected nucleus-bred 15-month rams for use at home, and the next cut of nucleus rams and some elite homebred rams were offered as breeding stock for sale. From 1993, restricted maximum likelihood methods were introduced to calculate breeding values, and across-age ram selection was applied. At the same time, the nucleus ewes were re-distributed across all Members' flocks, and between-flock and between-year genetic links were main- tained by movement of sires for mating.

Estimates of total genetic progress by birth-year (obtaining data from Animalplan files, which were only available from 1986) were: WWT (1986-97) 1.83±0.17 kg (7.8% of the mean), YLW 2.76±0.24 kg (6.4%), YFW 0.23±0.01 kg (7.3%) and NLB (1986-95) 0.029±0.015 lambs (1.8%), and all flocks have contributed to the long-term genetic changes. Annual genetic trends over the period were approximately linear, except for YLW which appeared to show an increasing response rate. This is probably related to the extensive progeny testing carried out since 1994 to study sire families which appear to be elite for YLW, using progeny-test matings of rams to outside tester ewes. Segregation tests for a possible major gene have been carried out. Some evidence of bimodal distributions for YLW within sire was found, with a gene whose effect was +9% of the mean, in heterozygotes. Since 1993, secondary selection decisions based on FE have been complicated by across-flock selection, but genetic progress for this trait appears to be linear, with a heritability estimate for log (gamma glutamyltransferase; GGT) of 0.34±0.09. Over the birth years 1981-1997 there was genetic change in GGT by a factor of 0.71 (29% improvement), compared with a factor of 0.30 (70% improvement) over the same time period in the single-trait FE selection lines at Ruakura (Resistant versus Control lines).

Keywords: NZSAPAB; sheep; facial-eczema; genetic-selection; yearling-weight; major-gene.

Last Updated 06-08-1999