<b>Estimation of genetic and environmental relationships between milk yield and different measures of mastitis and hyperkeratosis in Holstein cows

Abstract

In this research, records of milk yield, mastitis occurrence and teats hyperkeratosis of 453 Holstein cows from a large herd with calving dates from December 2012 to December 2014 was used to estimate genetic and environmental correlations between milk yield, mastitis and hyperkeratosis. The highest and the lowest number of mastitis occurrence were in winter (January to March) and spring (April to June), respectively. Also, the highest and the lowest averages of days in milk at the time of mastitis occurrence were observed in winter and spring, respectively (162.53 vs. 29.67 days). The total number of mastitis occurrence was 151 times and in average a sick cow was infected 1.649 times. Obtained results showed low heritabilities for measures of mastitis (ranging from 0.048 to 0.134). Genetic correlations between measures of mastitis and milk yield were negative (from -0.502 to -0.183). Genetic correlation between hyperkeratosis and mastitis was positive which showed that selection for udder type traits would decrease mastitis occurrence. The results of this study can provide a background about the relationships between aforementioned traits and serve as a starting point for further study on these traits.

Keywords

• dairy cow
• genetic relationship
• iteration
• udder type