Question

In his Ph.D. dissertation, Dr. Moser found the following variances in a population of yearling Brangus cattle measured for fat thickness with ultrasound:

                                    σ²_BV = .001 cm²          σ²_E = .009 cm²

            Assuming variance of gene combination value is zero, calculate:

                        a.         Phenotypic variance of fat thickness

                        b.         Heritability of fat thickness

Based on the above, is a yearling heifer’s fat thickness a good indicator of her breeding value for that trait? Why or why not?

In her Ph.D. dissertation, Dr. Bormann found the following variances for age at first calving in a population of Angus cattle:

                                    σ²_BV = 767 d²              σ²_E = 1395 d²

            Assuming variance of gene combination value is zero, calculate:

                        a.         Phenotypic variance of age at first calving

                        b.         Heritability of age at first calving

Based on the above, is a yearling heifer’s age at first calving a good indicator of her breeding value for that trait? Why or why not?

Answer 1

Brangus Cattle:

Null Hypothesis: H0: Variance of gene combination value is zero

Alternate Hypothesis: H1: Variance is non zero

a. Variance(BV)=.001 cm2 and Variance(E)=0.009 cm2

Phenotypic Variance = 0.001+0.009 = 0.01 cm2

b. Heritability = H2 = V(Genetic) / V(Phenotypic)

= 0.001/0.01

= 0.1

Based on the above values we can say that, NO, yearling heifer’s fat thickness isn't a good indicator of her breeding value for that trait as the heritability is only about 10%.

Age at first calving:

Null Hypothesis: H0: Variance of gene combination value is zero

Alternate Hypothesis: H1: Variance is non zero

a. Phenotypic variance at the age of first calving = 767 + 1395 = 2162

b. Heritability at the age of first calving = 767/2162 = 0.35

Based on the above values we can say that, YES, yearling heifer’s fat thickness is a good indicator of her breeding value for that trait as the heritability is only about 35%.