@conference {41222,
	title = {Factors affecting the sex ratio of dairy cattle in New Zealand},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {60},
	year = {2000},
	month = {Jan},
	pages = {301-302},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Hamilton},
	abstract = {The sexes of calves born in 1996 (n = 319,539) and 1997 (n = 408,381) to artificial insemination in selected herds were analysed to study the effects of region, dam breed, dam age, semen type, semen breed, semen age, and sires on the sex ratio of calves. There was a significant (P < 0.001) effect of semen type on sex ratio; frozen semen resulted in 1.66\% and 1.24\% more male calves than fresh semen, respectively, in the 1996 and 1997 seasons. There was also significant (P < 0.01) variation among sires in sex ratio, but the heritability estimate for sex ratio was low (h2 = 0.02). No other effects were significant. Industry-wide use of fresh semen will result in more heifer calves from which future replacements can be selected. },
	issn = {1176-5283},
	author = {Xu ZZ and Johnson DI and Burton LJ}
}
@conference {40767,
	title = {Assessment of female traits for genetic improvement of fertility in dairy cattle},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {56},
	year = {1996},
	month = {Jan},
	pages = {27-31},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = { The objective of the present study was to investigate the suitability of  various fertility traits for describing the reproductive performance of dairy  cows in New Zealand. Using a data set from herds participating in the  Livestock Improvement Sire Proving Scheme over the 1986/87 to 1992/93  seasons, the following female fertility traits have been investigated. Based  on the start of mating (STOM) in a particular herd, the intervals from STOM  to first mating (SMFM) and to the successful mating (SMCO) were  calculated and compared to the internationally used traits that are based on  the calving date, such as, calving to first mating (CFM) and calving to  successful mating (days open, DO). Further traits considered are age at  calving (AC), number of matings per conception (NS), first to successful  mating (FMCO), calving interval (CI) and two traits that indicate whether a  cow became pregnant within 21 or 42 days of STOM (PR21, PR42). The  traits defined for the unique conditions in New Zealand, SMFM, SMCO,  PR21 and PR42 emphasize the economic importance of reproduction to  dairy production. The comparison to overseas studies using DO, FMCO and  CI showed that New Zealand dairy cows had a better fertility performance  than overseas cows.},
	issn = {1176-5283},
	author = {Grosshans T and Xu ZZ and Burton LJ}
}
@conference {40770,
	title = {Genetic parameters for fertility traits in seasonal dairy cattle},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {56},
	year = {1996},
	month = {Jan},
	pages = {38-41},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {Genetic parameters for female fertility traits in New Zealand dairy  cattle have been estimated using a data set of herds participating in the  Livestock Improvement Sire Proving Scheme. In total, 66294 records of  both pure and crossbred Friesian, Jersey and Ayrshire cows in their first  lactation were used. The highest heritability estimates were .134, .058, .037, .037, .029 for age at  calving (AC), interval from start of mating (STOM) to first mating (SMFM),  interval from STOM to conception (SMCO), pregnancy rate at day 21 or 42  after STOM (PR21) or (PR42), respectively. Low heritabilities were  obtained for first mating to conception (FMCO), calving interval (CI) and  number of services (NS) (<.017). Genetic correlations between CI and either  SMFM or SMCO where high (.920 or .957). Genetic correlation between  SMCO and PR21 or PR42 is close to one. Therefore the later three traits are  identical from the selection point of view. For AC, genetic and phenotypic  correlations with milk production traits were high and unfavourable.  Antagonistic genetic correlations also existed between milk yield and the  fertility traits and between SMFM, SMCO, FMCO or NS and fat or protein  yield. The unfavourable genetic correlations between milk production and fertility  traits strongly suggest that fertility performance should be incorporated into  the breeding objectives of New Zealand dairy cattle. Based on their  heritability estimates, their genetic coefficients of variation and their genetic  correlations with production and other fertility traits, it is recommended that  SMFM and PR21 (or its more easily obtainable equivalent trait 2-to-24-day  non-return rate, 2-24NRR) should be used as selection criteria. In addition,  the incidence of use of treatment programmes for overcoming fertility  problems, such as induction of calving and anoestrus treatment, should also  be incorporated into the selection index.},
	issn = {1176-5283},
	author = {Grosshans T and Xu ZZ and Burton LJ and Johnson DL}
}
@conference {40769,
	title = {Reproductive efficiency in lactating dairy cows},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {56},
	year = {1996},
	month = {Jan},
	pages = {34-37},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {Both genetic improvement and milk yield of dairy cows are dependent  on a high reproductive performance. Under normal situations, oocyte  fertilisation rates following insemination at the appropriate time are high  (>90\%) and gross genetic defects in embryos are estimated to be around  10\%. This means that the biological limit of conception rate should be  around 80\%. Such a performance has rarely been realised in practice, with  60\% being a normal target for lactating cows in New Zealand dairy herds.  At a herd level, reproductive performance is best measured by the  percentage of cows pregnant within a period after start of the breeding  season and this is determined by the combination of submission rate and  conception rate. Major factors that affect reproductive performance in New  Zealand dairy herds include anoestrus, errors in heat detection, fertilisation  failure and embryo mortality. Given adequate nutrition, herd management is  undoubtedly the major determinant of reproductive efficiency. The low  reproductive efficiency in dairy cows creates a bottleneck to genetic  improvement and is a major factor affecting milk production efficiency. },
	issn = {1176-5283},
	author = {Xu ZZ and Burton LJ}
}
@conference {40724,
	title = {Reproductive performance of synchronised lactating dairy cows},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {55},
	year = {1995},
	month = {Jan},
	pages = {242-244},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	abstract = {The objective of this trial was to evaluate the reproductive performance  of lactating dairy cows following oestrous synchronisation with a  combination of progesterone, oestradiol and prostaglandin. Cycling cows in  11 herds were randomly divided, with restriction to age, calving date,  condition score and breed, into synchronised (n=1332) groups. Those in the  synchronised group were each treated with an EAZI-BREED},
	issn = {1176-5283},
	author = {Xu ZZ and Burton JR and Burton LJ and Macmillan KL}
}
