Dairy cattle

Genetic parameters for lactation yields of milk and milksolids of New Zealand dairy cows undergoing standard and extended lactations

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Abstract

Extended lactations, beyond the 12-month calving interval typical of pasture based dairy systems, has been proposed as a way of reducing the number of calvings per year, flattening seasonal peaks in labour demand and reducing the number of non-replacement calves. Cows in pasture-based systems, however, have been selected for high merit for farm profitability in an annual cycle but their productive performance may differ under extended lactation. The objective of this study was to estimate genetic parameters for lactation yields of milk and milksolids (fat plus protein) of dairy cows undergoing standard and extended lactations. The data set comprised 19,154 standard (4.2 herd-tests on average) and 5,223 extended (7.9 herd-tests on average) lactation records from 2,791 Holstein-Friesian, 1,130 Jersey and 3,893 Holstein-Friesianà—Jersey crossbred cows calving between 2008 and 2023 in 14 herds. A total of 1,197 sires and 769 maternal grandsires were represented. A lactation was considered to be extended when the herd-tests occurred between 15 and 670 days in milk. Persistency of lactation for milksolids was defined as (B/A)à—100 where A is milk produced from day 1 to 305 and B is the total milk produced from day 306 up to 610. The average (±SD) yields for standard lactations were 4,427±1,701 L milk and 381±139 kg milksolids from an average of 254±48 days in milk. The average (±SD) yields for extended lactations were 7,678±2,879 L milk and 682±225 kg milksolids from an average of 485±52 days in milk.Estimates of (co)variances were obtained using the ASREML program with bivariate animal models. The model included the fixed effects of herd-year and month of calving, age at calving and breed group, and random additive genetic and residual effects. Heritabilities for standard lactation yields of milk and milksolids were 0.40 and 0.29, respectively. Corresponding heritabilities for extended lactations were 0.40 and 0.30. Estimate of heritability for milksolids persistency in extended lactation was 0.34. Estimates of genetic correlation between milk and milksolids yields were 0.70 and 0.67 in standard and extended lactations, respectively. The genetic correlations of the same trait, but expressed as standard and extended lactation, were 0.74 and 0.62 for milk and milksolids, respectively. Estimates of genetic correlations of milksolids persistency with milk and milksolids yields in extended lactations were 0.53 and 0.71, respectively. The results indicate that sires and cows ranking high for milksolids in standard lactation would not rank high for milksolids and persistency in extended lactations.

Keywords: 2026

How to Cite:

Lopez-Villalobos, N., Bird, S. & Edwards, J., (2026) “Genetic parameters for lactation yields of milk and milksolids of New Zealand dairy cows undergoing standard and extended lactations”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2282814. doi: https://doi.org/10.31274/wcgalp.23470

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