@conference {41280,
	title = {Factors associated with the incidence of {\textquoteright}Phantom cows{\textquoteright} in Australian dairy herds},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {61},
	year = {2001},
	month = {Jan},
	pages = {180-183},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Christchurch},
	abstract = {A major cause of delayed pregnancy and reproductive wastage in Australian dairy cattle is the failure of cows to be re-inseminated within 24 days of an unsuccessful insemination. Four commercial herds were observed to determine the incidence of this syndrome. Those cows inseminated in the first three weeks of the mating season (n=721 cows) were observed for a subsequent return to service, and non-return cows were diagnosed for pregnancy. Overall, 45\% of cows were confirmed pregnant to first service, 37\% returned to service within 24 days, and 19\% were diagnosed as non-return, non-pregnant cows (Phantom cows). The majority of cases of Phantom cows (89\%) were explained as having: a) a CL but not returning for service; b) having an abnormally long return to service (25 to 39 days); or, c) reverting to an anoestrous state. Other cases (<5\% incidence) included ovarian cysts, pyometra and uterine adhesions. Repeated diagnoses of pregnancy identified few cases in which a pregnancy appeared to have failed (3.3\%). The incidence of Phantom cows was higher for CIDR-treated anoestrous cows than cows synchronised with prostaglandin, and lowest for those cows not treated. These observations form the basis for further study of this syndrome in Australian herds. },
	issn = {1176-5283},
	author = {Nation DP and Morton J and Cavalieri J and Macmillan KL}
}
@conference {40993,
	title = {Factors influencing the prevalence of postpartum anoestrus in New Zealand dairy cows},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {58},
	year = {1998},
	month = {Jan},
	pages = {79-81},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {The aim of this study was to determine the association between age, interval from calving (PPI) and breeding worth (BW) and prevalence of postpartum anoestrus (AA), as well their effect on response to hormonal treatment by anoestrous dairy cows. Individual cow details were collated from 6649 cycling and 2446 AA animals in 29 herds. Probability of AA was influenced by herd and was negatively related to PPI and age (p<0.001); but was not related to BW (p>0.05). Response of AA cows to treatment with progesterone and oestradiol benzoate was evaluated using a subset of 1482 anoestrous cows. Within 7 days of treatment, oestrus was detected in 87.1\% cows and conception rate to insemination during this period was 42.2\%. Oestrous response varied between herds but was not influenced by BW, PPI or age (p>0.1). Conception rate was positively related to PPI (p<0.001), but was not influenced by BW or age (p>0.1). It is concluded that in commercial dairy herds the likelihood of a cow being AA is greatest in young and recently calved animals, but is not influenced by breeding worth.},
	issn = {1176-5283},
	author = {Rhodes FM and Clark BA and Nation DP and Taufa VK and Macmillan KL and Day ML and Day AM and McDougall S}
}
@conference {40996,
	title = {Ovarian volume is a predictor of the resumption of spontaneous oestrous cycles but not the response to the treatment of anoestrus.},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {58},
	year = {1998},
	month = {Jan},
	pages = {88},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {This study examined the use of a classification system for ovarian activity as a predictor for both the spontaneous resumption of oestrous cycles and for reproductive per-formance after treatment for anoestrus.},
	issn = {1176-5283},
	author = {Nation DP and Rhodes FM and Day AM and Macmillan KL}
}
@conference {40944,
	title = {Effect of hormonal environment at emergence on persistence of ovarian follicles in cattle},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {57},
	year = {1997},
	month = {Jan},
	pages = {239-240},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {Reduced fertility often occurs when progestins are used to control the timing of oestrus in cattle and is espe-cially evident when a corpus luteum (CL) is not present in the ovary (Kinder et al., 1996). The lowered conception rates at the synchronised oestrus are associated with the development of abnormally large, {\textquotedblleft}persistent{\textquotedblright} ovarian fol-licles as a result of increased secretion of LH. An under-standing of the endocrine regulation of persistent follicles is essential for development of methods to prevent ovula-tion of this aberrant structure in progestin-based oestrous control systems. The influence of time of luteal regression relative to follicle emergence on persistence of dominant follicles was evaluated in progestin-treated cows.},
	issn = {1176-5283},
	author = {Day ML and Burke CR and Nation DP and Rhodes FM and Macmillan KL}
}
@conference {40939,
	title = {Efficacy of an anoestrous treatment for dairy cows is reduced if administered within 3 weeks of calving.},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {57},
	year = {1997},
	month = {Jan},
	pages = {228-230},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {The effect of treating dairy cows with anovulatory anoestrus (n=660) at various intervals post-partum was investigated. Treatment consisted of priming with progesterone using an intravaginal device (CIDR-B) for 6 days, with an injection of oestradiol benzoate 24h after device removal. The mean interval from treatment termination to conception tended to be greater for cows calved less than 3 weeks at diagnosis than contemporaries calved at least 3 weeks (32.8 6.3 vs 23.7 {\textpm} 1.1 days; p<0.1). Final empty rate was higher for cows diagnosed and treated within 3 weeks post-partum (39\% vs 13\%; p<0.001). Survival analysis accounted for the higher empty rate to determine the probability of pregnancy over time. Cows calved less than 3 weeks at treatment had a lower probability of pregnancy than contemporaries calved at least 3 weeks (p<0.01). This study found a negative effect of treating anoestrous cows within 3 weeks post-partum. Further work should define the nature of this problem and the value of delaying treatment until at least 3 weeks after calving. },
	issn = {1176-5283},
	author = {Nation DP and Macmillan KL and Taufa VK}
}
@conference {40945,
	title = {The responses of lactating cows treated for anoestrus to an oestradiol capsule or an oestradiol injection.},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {57},
	year = {1997},
	month = {Jan},
	pages = {241},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {Postpartum anovulatory anoestrus is a mjor form of infertility among cows in dairy herds inNew Zealand. The currently recommended treatment involves a 5-day prim-ing with progersterone (P4) released from a CIDR TM device (InterAg, NZ), with a 10 mg gelatin of oestradiol benzoate (ODB) and 1 g lactose capsule (CIDR TM; InterAg, NZ) placed in the grooved surface of the device preceding device insertion, and an injection of ODB (CIDIROLTM ; InterAg, NZ) given intramuscularly at 24 to 48h following device removal.},
	issn = {1176-5283},
	author = {Taufa VK and Macmillan KL and Nation DP and Day AM and Ashcroft MJ}
}
