Selection for Type and Production and Influence on Herd Life of Holstein Cows

Abstract

Average indexes describing selection for productive merit were estimated from 7,079 records in six herds cooperating with The Ohio North Central-2 project. The average indexes included various combinations of yield information and first lactation type score. In most cases the terminal lactation of a sequence received more attention than earlier lactations. Attention to type score relative to milk yield was greater in four of the six herds.Efficiency of each index to describe selection for productive merit was evaluated. In all herds the average index was more efficient in describing selection than single lactation traits. Efficiencies of average indexes describing selection for second lactations were .31, .43, .52, .43, .36, and .48 in the herds.Two measures of herd life were used to partition the direct effects of first lactation yields and type score. Yield and type score accounted for 6 to 21% of the variability in herd life. Type score was .81, 1.86, .38, .47, .85, and 1.65 as important as milk yield in determining the months of productive life in the six herds.