@conference {40853,
	title = {Patterns of oestrus vary with different forms of synchrony},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {56},
	year = {1996},
	month = {Jan},
	pages = {347-349},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {The original objective of a trial conducted in 3 herds of Friesian  heifers was to compare pregnancy rates obtained when each animal was  synchronised and then inseminated at about 50 h after removal of a  subcutaneous ear implant (CrestarTM) or an intravaginal device  (GenermateTM). Because most of the heifers in the CrestarTM group were  in oestrus before any of the herdmates treated with the GenermateTM  system, the CrestarTM treated heifers were inseminated at either 28 h or 50  h after implant removal. Over the 3 herds, 64\% of 153 heifers treated with Crestar were in oestrus by  28 h after implant removal compared to 7\% of their GenermateTM treated  (n=155) herdmates (P<0.01). The average pregnancy rate to first  insemination of 56.3\% was similar for both synchrony treatments, and for  the two insemination times in CrestarTM treated heifers. The earlier onset of oestrus in heifers treated using the CrestarTM system  was possibly associated either with persistent and dominant ovarian  follicles, or to the injected oestradiol valerate producing behavioural  symptoms of oestrus. Nonetheless, inseminating heifers with a shortened  interval to oestrus at 28 h rather than 50 h after implant removal may avoid  reductions in pregnancy rate which occur with inseminations made after the  end of oestrus, or with heifers which ovulate a persistent dominant follicle. },
	issn = {1176-5283},
	author = {Macmillan KL and Taufa VK and Morris GR}
}
