Sustainability & efficiency

The genetic relationship between liveweight in dairy youngstock and lactating cows in New Zealand dairy cattle.

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Abstract

Live weight (LWT) is an important trait in dairy and beef cattle production systems in New Zealand. In the absence of feed intake records LWT can be used as a proxy for efficiency. Previous studies have indicated that incorporating LWT into a selection index in New Zealand grazing systems, alongside milk, fat, and protein, resulted in an additional economic gain of 3-5% compared to selection based on an index without LWT. LWT was introduced into New Zealand's dairy cattle selection index in 1996. Phenotypic recording of LWT from lactating dairy cattle is limited (approximately 40,000 animals/yr); most records are collected from first lactation heifers in sire-proving scheme herds. However, LWT recording of dairy youngstock is a routine farm management practice to monitor growth. Over 1 million youngstock LWTs are recorded annually. This study aimed to estimate variance components and genetic parameters for LWT in the New Zealand multi-breed dairy heifer population, to determine if youngstock LWT could be used as a source of phenotypes for the genetic evaluation of LWT. Animals with a minimum of 2 LWT records between birth and 365 days of age and 2 LWT records between 366 and 700 days were included. A total of 10,949,191 LWT records from birth to 24 months for 1.3m dairy heifers and 30,000 dairy bulls born between 2008 and 2022, along with a full pedigree of animals, were analyzed using a multi-trait model. LWT at different ages was defined: LWT1 (birth to 1 month), LWT2 (6 months), LWT3 (12 months), LWT4 (18 months). A subset of 70,063 females within the full dataset had LWT records during lactation (96,397 records), between 24 and 36 months of age (LWT5). The analysis was conducted using APEX - Linear Model Suite with a multi-trait model considering the fixed effects of sex, contemporary group of herd-year-month of weight, breed (Jersey, Holstein, Friesian, Red Dairy Cattle), heterosis effects, an individual's (pedigree-based) inbreeding coefficient, genetic group covariates, random genetic effects, and random residuals. Mean LWT increased from 79.6 kg at LWT1 to 401 kg at LWT4 and 420 kg at LWT5. Heritabilities ranged between 0.4 and 0.65. LWT1 had the weakest genetic correlation with LWT5 (0.77). The strong ( ≥0.9) genetic correlation between LWT5 and LWT3 and LWT4 suggests that LWT from ≥ 12 months of age could be used to predict breeding values for mature LWT.

Keywords: 2026

How to Cite:

Harris, B., Ismael, A., McNaughton, L., Sherlock, R. & Spelman, R., (2026) “The genetic relationship between liveweight in dairy youngstock and lactating cows in New Zealand dairy cattle.”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2284521. doi: https://doi.org/10.31274/wcgalp.23574

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