@conference {40400,
	title = {Melatonin secretion in Romney ewes differing in wool growth and reproduction is not aligned to photoperiod during spring and summer},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {52},
	year = {1992},
	month = {Jan},
	pages = {149-152},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	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.  },
	issn = {1176-5283},
	author = {Scott IC and Heath D and Hawker H}
}
