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.
New Zealand Journal of Animal Science and Production, Volume 82, Online, 93-98, 2022
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