Abstract

A progeny test involving Romney (n=5) and Poll Dorset (n+5) rams mated to Romney ewes was conducted to examine the relationship between testis size and endocrine parameters, measured during the transitional period from the non-breeding to the breeding season, in rams, and reproductive performance of their daughters in the first and second breeding seasons. More of the Poll Dorset cross hoggets reached puberty during the first breeding season (80 v. 60%; P<0.01) associated with earlier onset (13 v. 22 May; P<0.10) at younger ages (264 v. 276 days; P<0.10) and more oestrous cycles (2.7 v. 2.0; P<0.05) than for Romney hoggets. The date of onset of the second breeding season was influenced by breed (P<0.001) and sire within breed (P<0.05). These differences between Romney and Poll Dorset cross animals in reproductive performance were associated with differences between their sires in the pattern of seasonal variation in testis size and plasma gonadotrophin concentrations. However, within-breed correlations between testicular and endocrine parameters in the sires and date of onset of the breeding season in the offspring were low. It is concluded that, while some of the testis and endocrine parameters could potentially be used as selection criteria for date of onset of the breeding season in ewes, further studies are needed before these parameters can be incorporated into selection programmes.

IC, Scott, D Heath, and H Hawker

Proceedings of the New Zealand Society of Animal Production, Volume 52, , 149-152, 1992