Observations on the Degree of Expression of Estrus in Cattle

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Abstract
The degree of expression of heat symptoms was scored on 554 first-calf beifers sired by 29 different sires and distributed among 6 Danish progeny-testing stations. These scores ranged from 1 for faint expression of heat to 4 for strong expression of heat. The heritability of the expression of heat was 0.21. Those heifers that conceived at 1st service had a significantly higher rating for expression of heat than those that failed to conceive, the difference being 0.22 unit. Those that conceived at 2nd service had a significantly higher rating than those that failed to conceive, the difference being 0.17 unit. By scoring cows 0 for failure to conceive, or 1 for conceiving, the heritability of conception was 0.040 and -0.037, for 1st and 2d services, respectively. These estimates are small, and they bracket zero; consequently, the heritability of conception is probably small or zero. The within-progeny-group correlations between conception and the expression of heat were 0.154 and 0.129 for the 1st and 2d service data, respectively. On a basis of first-service data, the regression of the genetic value for conception on the expression of heat was 0.065 rGxGy, where rGxGy is the correlation between genetic values for conception and expression of heat. Ratings for the degree of expression of heat are of little or no value in selecting for an increased conception rate.