The effect of cow genetic index and grass-based feeding system on the performance of spring-calving Holstein-Friesian cows in second lactation

Abstract

AbstractThe objective of this study was to investigate the effect of both cow genetic index (CGI) and feeding system on the performance of second lactation Holstein-Friesian dairy cows on grass-based feeding systems. There was no interaction between CGI and feeding system for any of the parameters measured. Cows of high genetic index (HGI) produced significantly higher yields of milk (P < 0.001), fat (P < 0.001) protein (P < 0.0001) and lactose (P < 0.001) than medium genetic index cows (MGI). CGI had no effect on the concentration of milk constituents. Averaged across four intake measurements the HGI cows had significantly (P < 0.001) higher grass dry-matter intake (GDMI) and total dry-matter intake (TDMI). Live weight was similar for both genotypes during lactation. The HGI cows had significantly (P < 0.05) higher live-weight loss in the first 10 weeks of lactation, significantly lower live-weight gain from week 10 to the end of lactation and higher (P < 0.05) live-weight gain during the dry period. Condition score was significantly lower with the HGI (P < 0.001) at all stages of lactation. There was a higher proportion (P < 0.05) of the HGI cows non-pregnant at the end of the 13-week breeding season. Feeding system had a significant effect on the yield of milk (P < 0.001), fat (P < 0.001), protein (P < 0.001) and lactose (P < 0.001). Feeding system B produced significantly higher (P < 0.05) milk yield and yield of constituents (when compared with feeding systems A and C). Over the period when feeding systems were being applied, feeding system C had significantly higher (P < 0.05) milk protein concentration. Feeding system had a significant effect (P < 0.001) on both GDMI and TDMI. Feeding system had no effect on live weight, condition score or fertility performance.