GENETIC AND PHENOTYPIC CORRELATIONS BETWEEN FERTILITY AND MILK COMPOSITION TRAITS OF FRIESIAN X BUNAJI COWS

This study was conducted to determine the genetic and phenotypic relationship between fertility and milk production traits of sixty F 1 Friesian x Bunaji dairy cows, whose parity ranged from 1 to 5. Four  fertility traits; days to first insemination (DFI), days open (DO), Non-return rate 56 days after first insemination (NRR56) and numbers of insemination per conception (NIC) were evaluated. The milk composition variables {(milk fat content (MFC) and milk protein content (MPC)}, were analyzed weekly from 4 to 305day post-partum. The data were analysed using sire model to estimate the genetic parameters. The estimates of heritability (h 2 ) for fertility traits were low and ranged from 0.014 to 0.035. The genetic correlations were generally stronger than the phenotypic correlations, but the direction of the relationship was similar. The genetic correlation ranged from -0.095 to 0.485 while the phenotypic correlations ranged from -0.009 to 0.235. The magnitude and direction of the estimated genetic correlation coefficients between milk yield and fertility traits were unfavourable; cows selected for high milk yield may have prolong interval to insemination after calving (DFI = 0.435) due to delay in resumption of ovarian activity (DO = 0.485) and may require high number of insemination per conception (NIC = 0.299) and therefore, are not likely to become pregnant within 56 days after the first insemination (NRR56 = -0.044). The genetic correlation between milk fat content (MFC) and fertility of dairy cows in early lactation was also unfavourable; high MFC in early lactation is associated with poor fertility,  decreased conception rate to first services (DFI = 0.290), prolong calving to conception interval (DO = 0.216) and increased number of service per conception (NIC= -0.197). However, cows with high milk protein in early lactation are likely to have shorter intervals to first insemination after calving (DFI = - 0.290), with high probability of first insemination conception rate (NIC = -0.114) and therefore, are likely to become pregnant within 56 days after first insemination (NRR56 = 0.096). In conclusion, there is a close relationship between milk composition yield and fertility, such that increase milk and composition yield is associated with lower fertility of dairy cows, decrease conception rate, prolong calving to conception interval and increase number of insemination per conception.