@conference {41667,
	title = {Effects of artificial insemination on the incidence of long return intervals},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {66},
	year = {2006},
	month = {Jan},
	pages = {325-328},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Napier},
	abstract = {The Phantom Cow Syndrome is a major impediment to achieving compact conception patterns in Victorian herds. Some inseminated cows fail to return for a further insemination even though they are not pregnant because the corpus luteum formed following insemination is maintained for an extended period. Five years of records were obtained from a herd of Holstein cows in Northern Victoria. Each cow was fitted with a hock tag that combined electronic identification with pedometer monitoring for oestrus. It was the only detection method used within a herd of up to 550 cows that had three AB programs of 6 to 8 weeks in each year. There were periods when cows detected in oestrus would be inseminated and others when they would not. Records were available for 2777 inseminations. The return intervals following these inseminations were classified as: Short (<18 days); Normal (18 to 24 days); or Long (>24 days). The overall conception rate for the 2777 inseminations made from 41 days to 160 days post-calving was 41.7\%. The 417 Long intervals represented 15\% of all inseminations and 25.8\% of cows not confirmed pregnant to a preceding insemination. Only 54 of 1459 oestrus events (3.7\%) not associated with an insemination were followed by a Long cycle (P<0.001). The proportion of Long returns declined linearly from 19.9\% among the 738 cows inseminated from 41 to 60 days post-calving to 7.4\% among the 189 cows inseminated from 141 to 160 days post-calving. These results demonstrated that the percentage of Long return intervals increased significantly following insemination. The magnitude of this increase declined with an increase in the interval from calving to insemination. },
	issn = {1176-5283},
	author = {Pino CS and Macmillan KL and Anderson GA}
}
@conference {41671,
	title = {Variation in yields of milk and milk solids in Holstein cows induced to calve prematurely},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {66},
	year = {2006},
	month = {Jan},
	pages = {344-349},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Napier},
	abstract = {Milk production was compared between multiparous Holstein cows that were induced to calve and herdmates that calved spontaneously at approximately the same time in 88 dairy herds from Victoria and Tasmania. Yield averages for each herd were calculated for induced and spontaneously calving cows for milk volume, milkfat and protein during the first 120 days of lactation and for 305 days. Associations between induced and spontaneously calving groups for 305-day yields were described using linear equations. Slopes ranged from 0.82 (for milk yield) to 0.87 (for protein yield) and R2 values ranged from 0.84 to 0.88 (P<0.001). The average reduction in milk yield over the 88 herds was 366 litres (7\%). The estimated milk yield reduction for induced groups in herds where spontaneously calving contemporaries averaged only 3500 litres per 305 days was 40 litres (1.1\%) compared to an average estimated reduction of 915 litres (11\%) in herds averaging 8500 litres. Similar proportional reductions were calculated for 305-day yields of milkfat and protein. Collectively these results show that yield reductions following induced premature parturition are substantially higher in absolute as well as proportional terms in herds with higher milk yields. },
	issn = {1176-5283},
	author = {Jaques SA and Macmillan KL and Anderson GA and Morton JM}
}
