Abstract

The objective of this study was to investigate causes of reduced peak milk yield of autumn-calving cows. This experiment is part of a study that is comparing autumn- and spring-calving systems. Two groups of 17 multiparous, Friesian cows that had calved between April 1 and May 6 were fed either ad libitum on grazed pasture (G), or restricted pasture (10kg DM/cow/day) supplemented with maize silage (6kg DM/cow/day) (G + MZ) for a period of 21 days. Milk yield by cows on G increased by 6.2 litres over the 21-day period and was significantly higher (P< 0.01) than the yields of cows on G + MZ. Milk prolactin concentration had no significant association with milk yield. There were higher average plasma concentrations of IGF-1 in the G group (range 104-140ng/mL vs. 95-107ng/mL) that corresponded to higher average milk yields but IGF-1 concentration had no significant association with milk yield. Milk yield and milk prolactin concentration were negatively associated with condition score and plasma IGF-1 concentration was positively associated with condition score.

J, Wrigley, C Holmes, and N Lopez-Villalobos

Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 210-212, 2001