Invited review: Carryover effects of early lactation feeding on total lactation performance in dairy cows.

In comparison with the intensive research on the direct effects of energy supply on dairy cow lactation performance, little attention has been paid to the effect of early lactation feeding on subsequent production. The present paper reviews 9 studies carried out with the aim of quantifying the immediate and subsequent responses in milk production and body weight to early lactation feeding. Most results showed that a more generous feeding in early lactation caused a positive carryover effect on subsequent production, whereas an inadequate level of feed in early lactation has been shown to reduce subsequent milk yield. The carryover periods ranged from 3 to 12 wk and the difference in milk yield between cows in the carryover periods ranged between 1.5 and 4.5kg of milk/cow per day. When calculated as a percentage of the immediate effect, the carryover effect ranged from 22 to 63%. In 2 of the 9 papers reviewed, the authors found no carryover effect, probably due to the long post-treatment periods in these studies. This is supported by the other studies in which the carryover effect was only significant in a limited period after end of treatment. The magnitude of the carryover effect seems to be determined by several factors including duration of the treatment and post-treatment feeding level. The most important factor though appears to be the magnitude of over- or underfeeding (i.e., a strong relationship between the treatment period feeding level and the subsequent response in production).