@article {3672,
	title = {Comparison of associations between estimated breeding values and cow survival in herds being milked once or twice a day},
	journal = {New Zealand Journal of Animal Science and Production},
	volume = {82},
	year = {2022},
	month = {01/2022},
	pages = {93-98},
	address = {Online},
	abstract = {The objective of this study was to investigate the link between estimated breeding values (EBV) for selected traits, including Traits Other than Production (TOP), and cow survival in herds milked once-a-day (OAD), and to contrast with herds milked twice-a-day (TAD). After filtering, data from 234 OAD herds (71,321 cows) and 234 TAD herds (75,123 cows) were extracted from the Dairy Industry Good Animal Database between 2007 and 2021. Cow survival from parities 1 to 2, 2 to 3, 3 to 4, 4 to 5 and 5 to 6 (S12, S23, S34, S45 and S56) were modelled within each milking frequency and age parity group, with trait EBVs fitted as covariables and the fixed effect of herd-year, using a generalised linear model with a gaussian kernel. The survival rate in OAD cows was higher than in TAD cows in S12 and less in S34 to S56. Udder support EBV became important in older cows (S45 and S56) but there were no significant differences between OAD and TAD herds. Compared to OAD herds, Fertility EBV had a greater effect on survival in TAD herds up to S34, as did Body Condition EBV for S12. Conversely, milk Volume, Fat, Protein and Somatic Cell Score EBVs had smaller effects on survival in TAD herds. Our results do not contain evidence that warrant greater selection pressure on functional traits in OAD systems relative to TAD to enhance animal survival. When selecting sires, selection pressure could be reduced on some traits, such as Fertility and Body Condition, in OAD systems, with a greater emphasis placed on production and milk composition.},
	issn = {1176-5283},
	author = {Edwards JP and Zhang X and Stachowicz K and Waters ACL and Amer PR}
}
@conference {3672,
	title = {Uncovering genetic variation in cow fertility using simulation},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {75},
	year = {2015},
	month = {07/2015},
	pages = {42-47},
	address = {Dunedin},
	abstract = { Dairy cow fertility is currently measured using two traits: the proportion of cows mated within 21 days of the start of mating
(PM21) and the proportion of cows that calve within 42 days of the start of calving (CR42). These traits indirectly measure a cow{\textquoteright}s
genetic propensity to return to a fertile state after calving. Both PM21 and CR42 have low heritability (0.05 and 0.03, respectively)
and fertility is suspected to have much stronger genetic drivers than indicated by these lowly heritable components. The purpose
of this study was to explore genetic and environmental factors that contribute to dairy cow fertility using a stochastic simulation
model. The model traces the reproductive life of cows from birth until their second calving date using environmental and genetic
variables to simulate fertility phenotypes. The model demonstrated that even when significant genetic variation was simulated
in underlying fertility traits, this variation appears only weakly as genetic effects using the current fertility traits evaluated for
genetic selection purposes. Potential alternative traits (e.g. gestation length, heifer puberty trait, strength of oestrus expression or
post-partum anoestrous interval) were shown to have potential to add value when identifying sires whose daughters calve earlier
in the season.},
	issn = {1176-5283},
	author = {Dennis NA and Stachowicz K and Visser B and Hely FS and Amer PR and Meier S and Burke CR}
}
