Responses in live weight change to net energy intake in dairy cows

Abstract

The objective of this analysis was to estimate the effect of increased energy intake on daily live weight changes during the first 100 days of lactation of primiparous and multiparous cows. A data set with 78 observations (treatment means) was compiled from 6 production trials from Denmark, Norway and Sweden representing the breeds Danish Holstein, Norwegian Red and Swedish Red. We had access to individual data for feed intake and live weight changes (every second week) during the first 100 days after calving. The data was grouped into sub datasets according to parity; either primiparous or multiparous. Feed ration energy values were recalculated by use of NorFor to obtain consistent energy expression in all trials as opposed to the varying feed evaluation systems used in original analysis of trials. Regression analysis with linear and quadratic effects were performed on live weight registrations for individual cows to stage of lactation, and daily live weight change was estimated from the slope at day 30, 60 and 90 after parturition. Data used for analyzes were treatment means given as the mean for a group of cows at a given treatment in a trial. Response models for daily live weight change were made by linear mixed effects model with trial as random factor. For both primiparous and multiparous cows there was an increasing curvilinear response at a decreasing rate to increased net energy intake and the daily live weight change at day 30 was negative and at day 90 it was positive for all energy intake levels. There were no effects of diet composition on the responses. At low energy intake levels primiparous cows had lower live weight losses than the multiparous cows. At mean net energy intake level for primiparous cows (116MJ) the daily live weight change at day 30, 60 and 90 were −0.37, 0.06 and 0.48kg/d, respectively and for multiparous cows at mean net energy intake (138MJ) the daily live weight change day 30, 60 and 90 were −0.38, 0.03 and 0.44kg/d, respectively. Following the response functions the marginal responses to increased energy intake decreased.