Udder volume (post milking) was determined in high and low breeding index (HBI;LBI) Jersey and Friesian cows. The difference in milk production of HBI and LBI Jersey herds (2 to 4 litres/day) was entirely attributable to difference in udder volume. This difference was generated during late pregnancy. Udder volume declined during lactation; 35 to 40% of udder volume at calving being lost by 20 weeks of lactation. There was no difference in udder volume between BHI and LBI Friesian cows measured at peak and in late lactation. Differences in production between these herds were due to increased udder productivity in the HBI animals (HBI, 2.0 litres/litre tissue/d; LBI 1.8 litres/litres tissue/d). Udder productivity in Friesians was 25% greater than in Jersey cows at peak and in late lactation. Milk yield and udder volume were significantly correlated (P<0.05) in Friesian and Jersey cows at all stages of lactation. Genetic selection of Friesian and Jersey cows has resulted in more productive animals in both breeds but through differing physiological mechanisms.
Proceedings of the New Zealand Society of Animal Production, Volume 45, , 13-16, 1985
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