The objectives of this analysis were to develop empirical prediction models for milk yield based on cow characteristics and dry matter intake (DMI) or net energy intake (NEL) and to evaluate the effect of breed, parity, stage of lactation and the additional prediction value of using NEL estimates versus DMI estimates for incorporation in future economical optimization models of the energy level in dairy cow rations. Previous Danish response models are outdated due to higher yield capacity of cows and the use of the new Nordic feed evaluation system NorFor since 2011. A data set with 195 treatment mean observations was compiled from original data of 13 trials from Denmark, Norway and Sweden representing the breeds Danish Holstein, Danish Red, Danish Jersey, Norwegian Red and Swedish Red. Total data were grouped into 4 sub datasets according to parity; either primiparous or multiparous and according to stage of lactation; either DIM 1 to 100 (Early) or DIM 101 to 200 (Mid). All analyzed ration characteristics were calculated from NorFor principles or estimated from NorFor feed table values. Data were analyzed using linear mixed effects model with trials as random effect. Residuals were weighted by number of cows in each treatment mean. Best fit model was by use of linear and natural log transformation of NEL intake rather than DMI in the regression, especially when also including the ration concentration of the individual nutrients (g/MJ NEL), neutral detergent fibre, amino acids absorbed in the small intestine and crude fat, in the model. Breed specific responses were parallel and only differed by their intercept. In early lactation for multiparous cows with a mean NEL intake (136. MJ) the model predicted an ECM response of 35.4. kg and for primiparous cows with mean NEL intake (115. MJ) the model predicted an ECM response of 27.8. kg. Marginal milk response (kg ECM/MJ NEL) decreased more for multiparous cows (from 0.34 to 0.08) than for primiparous cows (from 0.20 to 0.15) within the observation ranges of NEL intake.
Livestock Science, 2015, Vol 175, p. 59-69
Dairy cow; Energy intake; Meta-analysis; Milk production; NorFor