RELATIONSHIPS AMONG UDDER MEASUREMENTS, MILKING SPEED, MILK YIELD AND CMT SCORES IN YOUNG DAIRY COWS

Abstract

Heritabilities, phenotypic and genetic correlations among udder measurements (front teat length, front teat diameter, rear teat length, rear teat diameter, teat distance, udder height), milking speed, and milk yield were estimated for a Holstein line (H) and an Ayrshire-based line (A). Data from 1159 first lactation heifers in the National Cooperative Dairy Cattle Breeding Project were used. A subset of these data from 385 cows measured for the above traits plus California Mastitis Test (CMT) Score were analyzed to estimate relationships among udder measurements, milking speed, milk yield, and CMT score. Front teats were on the average 0.7 cm longer than rear teats. Heritability estimates of udder measurements, milking speed, and milk yield were moderate and ranged from 24% to 57% for the H line, 22% to 61% for the A line and 16% to 51% for the subset of data, except for teat distance in the H line which had a heritability of 5%. Heritability of CMT score was zero. Udders that were closer to the ground tended to have longer and wider teats. High-producing cows milked faster, had lower CMT score, and had udders closer to the ground than low producing cows. Genetic correlations of udder measurements with milking speed and milk yield were small and nonsignificant except for front teat diameter and teat distance which were negatively correlated with milk yield in H line heifers. Key words: Udder measurements, milking speed, milk yield, CMT score, dairy cattle