A rancher runs a closed herd of breeding cattle. He normally keeps and breeds th

Question

A rancher runs a closed herd of breeding cattle. He normally keeps and breeds the top 3% of his bull calves based on individual performance for yearling weight (YW). His sires average three years of age when their offspring are born. He is studying two female replacement strategies:

(Hint: Use the selection intensity chart in your book or slides)

Saving the top 20% of his heifers based on YW (Lf = 6.2 years)

Saving the top 60% based on YW (Lf = 3.2years)

If h2YW = 0.5, and ?PYW = 60 lb, calculate the expected rate of genetic change in yearling weight for each strategy.

What elements of the key equation is the rancher experimenting with?

What element appears to be more important?

Explanation / Answer

1. The h2 is narrow sense heritability.

In the given problem h2YW= 0.5

Where,

is predicted change

is accuracy of selection

is selection intensity

is genetic variation and

is generation interval.

The rate of genetic change can be increased by reducing the generation interval or by increasing selection intensity, accuracy of selection, or genetic variation.

2. Rancher is experimenting with elements like selection intensity and genetic variation in the equation.

3. Every element is important; the rate of genetic change can be increased by reducing the generation interval or by increasing selection intensity, accuracy of selection, or genetic variation. The elements accuracy and intensity increases generation interval. Accuracy for few sires decreases the intensity.

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