Genetic analysis of some diseases in Holstein cows in dairy herds of East Azerbaijan

In some studies, it has been reported that high milk production has a negative effect on animal health and longevity and affects the herd's profitability. Decreased cow health can affect herd profitability through increased rates of involuntary culling and decreased or lost milk sales. Common diseases in dairy cows include mastitis, abomasum displacement, lameness and reproductive disorders such as ovarian cysts and metritis. The objectives of this study were to provide a report on the reasons for culling in dairy herds, estimate the genetic parameters of production traits, diseases and to calculate the spearmen correlation between the breeding value of bulls for the traits and their breeding value for resistance for risk of culling.
Material and In this study, 31550 calving records from 17476 Holstein cows were used. In this study production data and culling reasons for diseases of 47 herds in East Azerbaijan from 1995 to 2012 has been analyzed. For genetic analysis ASReml software has been used. The investigated culling reasons for diseases were including of: mastitis, displaced abomasum, lameness, ovarian cysts and metritis. Estimation of disorders heritability has been obtained using univariate animal model. It has been presented a description statistics of culling reasons for diseases, estimation of genetic parameters of diseases and production traits in the studied dairy herds. Furthermore, correlation between bulls breeding value for culling reason for diseases traits and their breeding value for production traits has been calculated.
The average culling rates of dairy herds in this study was 7.05% (with a range from 2.04% to 26.98%). Results of this study showed that 55.24 % of animals in the herd were culling because of diseases and 44.76% for other reasons such as other diseases, physical injuries, non-economic and financial needs. In the other studies the average culling rate of Holstein dairy cows in northeastern Iran was reported as13.1% (4.4 to 25.3% per herd). Lameness and metritis's culling reasons had the highest heritability among studied traits with values of 0.28 ± 0.010 and 0.21 ± 0.045, respectively. A positive correlation (0.37) between mastitis and milk production was reported (Urib et al. 1995) suggesting that high milk production cows have a high genetic capacity for mastitis occurrence. The highest and lowest estimated repeatability in our study were for the traits of 305-day milk yield (0.47 ± 0.009) and fat percentage (0.25 ± 0.009), respectively. The spearman correlation showed positive correlation between breeding value for milk production and ones for displaced abomasum, lameness and metritis that were 0.197, 0.121 and 0.116, respectively. In the present study, there was a positive and significant correlation between the breeding value of bulls for culling due to displaced abomasum and ones due to lameness and ovarian cysts. So it seems the selection of bulls to resist against the risk of culling due to displaced abomasum helps them to resist against lameness and ovarian cysts diseases. Logistic regression results showed that all studied factors affecting culling due to mastitis. Logistic regression of culling risk factors due to displaced abomasum showed that age and season of parturition are important. Fleischer et al. (2001) reported a significant correlation between 305-day milk production and displaced abomasum disease. Logistic regression results showed that culling due to lameness is related to parity and 305- milk production. The selection of cows based on high milk production, milk fat percentage or body type characteristics could have adverse effects on the occurrence of diseases and resistance to health difficulties. So ignoring these negative correlations among traits in the selection process in the long term affects the dairy herd's profitability. The results of this study showed that about half of the culling percentages in the studied herds was unpredictable and due to diseases. Therefore, with considering of the resistance to diseases in selection strategies, it can be achieving to more survivability of the profitable herds.
The results indicate that most of the studied traits have positive genetic correlation with 305-day milk yield, so probably the cows with high potential for milk production are less resistant to culling for diseases. It is suggested that mastitis and metritis be taken into account in the breeding programs of Holstein dairy cows in the country.