A cattle rancher has determined the following variances for fat content in his h

Question

A cattle rancher has determined the following variances for fat content in his herd: Total phenotypic variance 100 Additive genetic variance 80 Dominance genetic variance 10 Environmental variance 10 Show your work in each question for partial credit. A. Calculate the total genetic variance. _______ B. Calculate the broad-sense heritability indicated by this data. ______ C. Calculate the narrow-sense heritability indicated by this data. ______ The rancher wishes to decrease fat content. If the average fat content in the starting population is 25% and he selects for breeding parents with an average fat content of 15%, what will be the expected average fat content among the offspring of the selected parents?

Explanation / Answer

A large number of estimates of heritabilities and variance components for SCC and/or SCS are reported in the literature for cattle, using either test-day or lactation models. Heritability estimates for single monthly test-day SCS range from 0.05 to 0.14 (i.e., Carnier et al., 1997; Mrode et al., 1998). Heritability estimates tend to increase slightly from the beginning to the end of the lactation due to a constant genetic variance and a decreasing environmental variance (Rupp and Boichard, 2003). The lactation measure of SCS, obtained by averaging the individual test-day records, shows a consistent higher heritability estimate with a range from 0.10 to 0.18.. Mastitis incidence is considered to have an important effect on culling decisions in dairy cows (Beaudeau et al., 1994; Gröhn et al., 1998; Neerhof et al., 2000), particularly mastitis occurring before the peak of lactation (Beaudeau et al., 1994). Correlations between breeding values for longevity and mastitis resistance, ranging from 0.22 to 0.33, were found in dairy cows (Nielsen and Pedersen, 1995)

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