New Zealand Journal of Agricultural Research abstracts

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Variations between years in the ram effect when Coopworth or Poll Dorset rams are introduced to seasonally anovular Coopworth ewes

I. C. SCOTT
P. D. JOHNSTONE

AgResearch
Invermay Agricultural Centre
Private Bag 50 034
Mosgiel, New Zealand

Abstract  Seasonally anovular Coopworth ewes previously isolated from rams were joined with either Coopworth or Poll Dorset entire rams for 28 days from either 6 January or 3 February in each of 3 successive years. Induction of ovulation varied between years, and more ewes ovulated when exposed to rams of either breed in February. When rams were introduced in January, more ewes exposed to Poll Dorset than Coopworth rams ovulated within 28 days of ram introduction. Onset of oestrus also varied between years and treatments. It is concluded that the variation in expression of the ram effect is probably governed by depth of anoestrus of the ewes at the time of joining.

Keywords  sheep; ewes; rams; Coopworth; Poll Dorset; breeding season; ram effect; ovulation; oestrus

PDF file of entire paper: medium quality (834K); (scanned from paper original: notes about this process)

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