Abstract
The problems of methodology and organization of selection of dairy cattle for resistance to mastitis by somatic cells of milk were studied. The necessity is justified and the procedure for converting the number of somatic cells (NSC) into a points score (PSNSC) is presented. The article provides evidence of the correspondence of the cows distribution curve by points for NSC to the Gauss curve, which is a sufficient reason to consider the NSC points score as a biometrically correct objective selection trait. Procedures for determining the indices of breeding value of bulls and their breeding categories by somatic cells in points are proposed. Requirements for the level of resistance in the cows and bulls selection are developed. The most resistant to mastitis are cows with a score of 3.9 points or less, and bulls with a breeding value index of -1.012 or less.
Highlights
In recent years, the role of genetic factors in reducing the frequency of mastitis in cows, a widespread and dangerous disease, has been actively investigated [1,2,3,4]
The objective of our research is to study ways to use the indicator of the number of somatic cells in milk as a selection method for increasing the resistance of dairy cattle to mastitis
To give the trait the properties of a normal distribution, the number of somatic cells (NSC) in milk in thousand/cm3 was transformed into point score (PSNSC) based on the binary logarithm and the recommended formula [15]: PS NSC = Log 2 (NSC / 100 000) + 3 (1)
Summary
The role of genetic factors in reducing the frequency of mastitis (udder inflammation) in cows, a widespread and dangerous disease, has been actively investigated [1,2,3,4]. When organizing the screening and selection of dairy cattle for mastitis resistance, the frequency of the disease in herds and populations is considered, as well as an indirect sign associated with mastitis – the number of somatic cells in milk (NSC) [5,6,7]. Ayrshire cows have been shown to have higher resistance to mastitis and a low level of somatic cells in their milk. In the United States, among the 6 dairy breeds, Ayrshires have the lowest linear NSC score 2.69, which indicates their higher resistance to mastitis. In Finland, Ayrshires have less NSC in milk than Holsteins – 164 against 187 thousand/cm3 [9]
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