Genotype and feeding system effects and interactions for health and fertility traits in dairy cattle

The effects of feeding system, genotype and genotype by feeding system inte ractions on a range of health and fertility traits were investigated in Hol stein Friesian cows at the Langhill Dairy Cattle Research Centre. There wer e two genetic groups: a selection (S) and control(C) line, housed and manag ed as one herd. Animals from each group were assigned to either a high conc entrate (HC) or low concentrate (LC) feeding system and offered approximate ly 2500 kg and 1000 kg; of concentrate per lactation on the HC and LC diets respectively. Feeding system had a significant effect on milk; fever, days to first service and days to first heat. Lactation number had a significan t effect (P < 0.05) on the incidence of mastitis, ketosis, retained placent as, milk fever and lameness and conception at first service. Effects of gen otype were investigated first by comparing the two genetic groups and then by regressions of the health and fertility traits on pedigree index for fat plus protein (PI). Significant effects of PI were found for oestrus not ob served, conception at first service, days to first heat, calving interval, days open and days to first service. The regression coefficient for mastiti s on PI was also significantly different fi om zero (P < 0.05). There were no statistically significant genetic line by feeding system interactions, i ndicating that the observed line differences applied to both dietary treatm ents. Heritabilities for the health traits ranged between 0.00 and 0.08 and for the fertility traits they ranged between 0.02 and 0.15. Selection for high genetic merit in this herd, seems to have led to a deterioration in fe rtility but not health traits (with the exception of mastitis), These resul ts, in line with those fi om studies in large populations, suggest that as genetic merit for production rises, fertility and some aspects of health ar e deteriorating. (C) 1999 Elsevier Science B.V. All rights reserved.