Age at first calving in UK Jersey cattle and its associations with first lactation 305-day milk yield, lifetime daily milk yield, calving interval and survival to second lactation.

Background: The association between age at fist calving (AFC) and production, fertility and survivability in Jersey heifers requires evaluation and comparison with published literature on Holstein heifers.
Method: Lactation records from 7256 pedigree Jersey heifers were grouped by AFC. Analysis comprised mixed effects multivariable regression modelling and binary logistic regression modelling.
Results: Increased lifetime daily yield (LDY) was significantly associated with a reduced AFC; calving UK Jersey heifers at 24 months or below is optimal. Heifers calving at 25-26 months had a significantly lower mean calving interval (391 days; 95 per cent CI 386 to 397) than those calving over 30 months (399; 95 per cent CI 394 to 405) (P=0.03). Heifers with an AFC over 30 months were less likely to survive to second lactation than those with an AFC 18-24 months. Spring calving heifers produced significantly less milk per day (9.87 kg; 95 per cent CI 9.64 to 10.1) than autumn (10.18; 95 per cent CI 9.94 to 10.41) or winter calvers (10.07; 95 per cent CI 9.84 to 10.3) (P≤0.01). Heifers that calved in the winter had a significantly shorter calving interval (389 days; 95 per cent CI 394 to 383) (P≤0.01) than heifers calved in other seasons.
Conclusion: The impact of AFC on Jersey production, fertility and longevity traits shows a similar trend to that seen in the Holstein, potentially on a lesser scale.
Competing Interests: Competing interests: None declared.
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