Short communication: correlated selection responses in somatic cell count from selection against clinical mastitis

Area of Science:

• Animal breeding and genetics
• Dairy science
• Animal health and welfare

Background:

• Somatic cell score (LSCS) is a key indicator of bovine mastitis and udder health.
• Genetic selection strategies in dairy cows can have unintended correlated effects on health traits.

Purpose of the Study:

• To estimate correlated selection responses in lactation mean somatic cell score (LSCS) in dairy cows.
• To compare the impact of selecting for high protein yield versus low mastitis frequency on LSCS.

Main Methods:

• Estimation of correlated selection responses in LSCS.
• Comparison between two selection groups: high protein yield and low mastitis frequency.
• Analysis of genetic differences after six generations of selection.

Main Results:

• Selection for increased milk protein yield led to an unfavorable correlated response in LSCS.
• Direct selection against clinical mastitis showed a favorable correlated response in LSCS.
• A genetic difference of 0.3 LSCS units was observed between groups after 6 generations, equating to ~15,000 somatic cells/mL.

Conclusions:

• Dairy cattle breeding for high protein yield may compromise udder health.
• Selection strategies targeting mastitis reduction positively influence udder health indicators like LSCS.
• Genetic antagonism exists between production traits and mastitis resistance in dairy cows.