Heifer Growth Effects on Milk Production, Days Open, Somatic Cell Count and Longevity in Norwegian Red Cows

Abstract

With the constant genetic improvement of Norwegian Red Dairy cows, there is a need to investigate whether the management for optimal production has been updated accordingly. The aim of this study was to further look into the effect heifer growth has on parameters important for milk production traits, in addition to the potential relationship between growth and longevity. Information about growth and milk characteristics from 421 dairy cows from a field trial conducted on 30 Norwegian dairy farms were used to test the former. Additionally, data from 514 cows with growth information was used to test if growth affected longevity. Our models pointed towards milk yield being most strongly affected by daily growth rate between 10-15 months of age. Besides these results, we generally found the most influential effects of daily gain in the prepubertal stage, with significant effects on the protein percentage in milk, days open (DO) and somatic cell count (SCC). While we found positive linear effects on milk yield and protein percentage, DO and SCC effects were curvilinear effect, indicating an optimum of around 800 grams/day for prepubertal growth. Also for longevity, we found a positive linear effect of prepubertal growth implying that the probability of culling became increased. This occurred when either taking account of the culling reason or not in the analysis, the ones increasing the probability of culling the most being low production, inferior fertility and temperament. Based on these findings, we argue that it is beneficial to aim for a more moderate daily growth rate in the prepubertal time period.