Changes in fatty acid composition of milk from lactating dairy cows during transition to and from pasture.

摘要

Effects of transition to and from pasture were investigated on the fatty acid composition of milk from 5 Holstein cows (cattle). A 45 day experiment was conducted on cows 347 +or- 111 days in milk, producing an average of 25.4 +or- 6.4 kg/day. For the 1st 2 days the cows were given a total mixed ration (TMR). They were then turned out to pasture for 29 days, before being returned to the TMR diet until the end of the study. Samples of milk collected in the morning and evening of each day were pooled and analysed daily for fatty acid composition. Milk CLA contents were 0.45% of total fat in the pre-pasture period and increased to 2.53% after 23 days in pasture, after which they remained constant. Milk fat C18:1t-11 contents were 2.8% of total fat during pre-pasture, increasing to a max. value of 7.95% after 22 days in pasture and remaining constant thereafter. C18:3 contents increased until day 7 on pasture, whereas C18:2 contents gradually decreased during transfer from TMR to pasture. 4 days after withdrawal from pasture, CLA contents returned to pre-pasture values.