Abstract

Effects of stage of lactation and season on mammary development and milk yield were determined in three herds of lactating Friesian cows (n~25 cows/herd) during June and July 1995. The herds in early, mid or late lactation calved in Apr-95, Jan-95 or Oct-94, respectively. Milk yield, in June, was higher in early and mid than in late lactation (16.1, 15.3 and 11.7 kg/d respectively, P<0.001). In July, yield was highest in early lactation and significantly lower with each successive stage of lactation (14.0, 12.5 and 10.4 kg/d, P<0.02). Yield decreased from June to July (14.4 to 12.3 kg/day, P<0.001) under increasingly severe nutritional/environmental influences. Udder capacity was higher in early and mid lactation than in late (16.1, 16.2 and 14.3 L, P=0.07), and decreased 18% from June to July (17.1 to 14.0 L, P<0.001). These results suggest that loss of mammary capacity is an important cause of declining milk production due to stage of lactation and season.

SJ, Eichler, and TB McFadden

Proceedings of the New Zealand Society of Animal Production, Volume 56, , 58-60, 1996