Faculty of Technical Sciences

Red dairy cattle (RDC) heifers, raised alongside Holstein (DH) heifers, often end up with higher body condition at first parturition compared to their DH pen mates. This difference has been hypothesized to be due to a better feedefficiency, but is yet to be tested. The aim of this study was to describe differences in growth, condition score, and feed efficiency due to breed and energy concentration of the diet in growing heifers. Three breed groups of 21 DH, 20 RDC and 21 DHxRDC heifers were included in the study. Within breed group, half the heifers were fed a standard heifer diet (STD) and the other half a diet with 15% lower net energy concentration (LOW). The experimental periodstarted at 5 months of age and ended at start of insemination at 14 months. Body condition score and live weight were measured monthly and daily feed intake was recorded using Insentec feed bins. The data was analysed using leastsquares means from a mixed model analysis. Across the whole period DH and DHxRDC heifers gained more body weight on the STD diet compared to the LOW diet (P<0.001). No significant difference was seen between STD and LOW diet in RDC (P=0.11). On the STD diet DH and DHxRDC grew better than RDC (P=0.001), whereas DH grew less than RDC and DHxRDC (P<0.001) on LOW. No significant difference was seen between RDC and DHxRDC with respect to growth (P=0.20). Higher BCS on the STD diet compared to LOW diet was seen in DH (P<0.001) and DHxRDC (P=0.03). No difference in BCS was seen between diets in RDC. RDC had the highest BCS among the breeds. DHxRDC had higher daily dry matter intake (DMI) (P<0.001) on the STD diet compared to DH and RDC. On the LOW diet, RDC had the highest DMI, with a small difference to DHxRDC (P=0.05). DH had the lowest DMI on the LOW diet. Comparing within breed RDC had similar DMI across diets, whereas DH and DHxRDC had lower DMI on the LOW diet. Results indicate that RDC and DHxRDC heifers perform better on a lower energy diet, compared to DH.