Methods of calculating breeding values for rams in flocks genetically linked by reference sires : A dissertation submitted in partial fulfilment of the requirements for the degree of Batchelor [sic] of Agricultural Science (Honours) in the University of Canterbury [Lincoln College]

Abstract

Weaning weight (WWT), hogget live weight (HLW) and hogget fleece weight (HFW) records from 9 Coopworth flocks, genetically linked by two reference sires, were used to compare four methods of ranking sires across flocks.

No change in sire rankings occurred (Pearson's correlation coefficient = 1.0) when home sire breeding values were calculated as deviations from reference sire breeding values and compared with a method using additive flock corrections based on the relative performance of reference sire progeny. Pearson correlation coefficients between breeding values calculated after flock general verses flock specific adjustment for environmental effects were 0.93, 0.87 and 0.96 for WWT, HLW and HFW respectively. The correlation coefficients between the method involving a combination of additive and multiplicative procedures and the additive only method were 0.97 for WWT and HFW and 0.92 for HLW.

Across flocks, single born lambs weaned 4.7 kg heavier than twins and 6.8 kg heavier than triplets while the corresponding differences for HLW (approximately 12 months of age) were 2.8 kg and 4.2 kg respectively and for HFW, 0.12 kg and 0.21 kg respectively. Rams were superior to ewes for WWT, HLW and HFW by 4.1 kg, 13.7 kg and 0.38 kg respectively. Lambs from 3 and 4 year old ewes were 1.5 kg heavier for WWT and 1.2 kg heavier for HLW than those from 2 year old ewes. 2 year old ewes left hoggets with fleeces 0.06 kg lighter than 3 year olds and 0. l kg lighter than 4 year olds. Progeny of 5 year old dams weighed 0.4 kg and 1.0 kg heavier than those of 2 year old dams at weaning and hogget weighing respectively while hogget fleeces from 5 year old dams were 0.04 kg lighter than those from 2 year old dams. Linear regression coefficients of WWT on birthday ranged between -0.068 and -0.276 kg/day while regression coefficients of age ranged from -0.002 to 0. 193 kg/day for HLW and from -0.005 to 0.016 kg/day for HFW. Considerable variation was apparent between flocks for birthrank, sex and age of dam effects.

The implications of these results have been discussed in relation to the optimal methods of ranking sires across flocks in practical breeding programs.