RESUMEN
Milk production and overall dairy farm economics depend on rearing dairy heifers. This study investigated the presence of a genotype by environment interaction in Holstein (HOL), Nordic Red dairy cattle (RDC), and their F1 crossbreeds (HOL × RDC) when provided different feed rations. The aim of our study was to assess how different energy concentrations in feed rations affect growth, BCS, feed intake, and feed efficiency in the 3 groups during the prepubertal period. The 3 breed groups were randomly allocated to receive either a standard or a low-energy feed ration. Holstein heifers exhibited reduced growth and a lower BCS when they were fed the low-energy feed ration. In contrast, the RDC heifers demonstrated similar growth rates with the different feed rations and maintained similar BCS irrespective of feed energy concentration. The HOL × RDC crossbred heifers performed as an intermediate between the HOL and RDC groups. Significant differences were observed in DMI and energy intake in the HOL and HOL × RDC groups depending on feed ration treatment. The RDC heifers had similar feed intake irrespective of treatment. There were no significant differences in the feed conversion ratio among breeds and feed treatments. These results indicate the presence of a genotype by environment interaction in prepubertal HOL and RDC heifers in response to differences in feed ration treatment. Due to the influence of prepubertal growth on future milk production, reproduction, and health status, it is important to be aware of breed-specific requirements during the prepubertal period, particularly in mixed breed and crossbred groups, to optimize growth rates and production potential.