Crossbreeding and the Benefits of Heterosis

By Dr. Matt Spangler, UNL Beef Genetics Specialist

The decision of whether or not to utilize a particular strategic system of crossbreeding depends upon individual production goals. First must come the blinding realization that no one breed excels in all areas that lead to profitability. In order to take advantage of breed complementarity, breeds must be paired such that they excel in different areas that are critical to the overall production goal(s).

Advantages of crossbreeding can be thought of as: 1) Taking advantage of breed complementarity, 2) Taking advantage of non-additive effects (dominance and epistatic) thus leading to capturing heterosis (hybrid vigor).

Too often heterosis (hybrid vigor) is thought to be the exclusive goal of crossbreeding. Heterosis is nothing more than an unexpected and often beneficial deviation from the average of the two parental lines. Hybrid vigor can also be thought of as the ‘anti-inbreeding’. Inbreeding increases uniformity by increasing homozygosity but also creates ‘inbreeding depression’ or a general decrease in survival and reproductive traits that can be caused by a decrease in heterozygosity. Percent heterosis can be calculated as:

% Heterosis = [(crossbred average – straightbred average) ÷ straightbred average] x 100

A simple example would be the percent heterosis realized in the average weaning weight from breeding a herd of Breed A cows to a group of Breed B bulls. Let 525 pounds be the average weaning weight of the F1 calves, 450 be the average weaning weight of the Breed A population, and 550 be the average weaning weight of the sire’s population.

The pounds of heterosis would be:

Pounds of heterosis = 525 – [(450+550)/2] = 25 pounds and the percent of heterosis would be: % heterosis = 25/[(450+550)/2] = .05 or 5%

The amount of heterosis that is realized for a particular trait is inversely related to the heritability of the trait. With that in mind, traits of low heritability (reproductive traits) generally benefit from heterosis the most. They generally have a heritability of less than 10% and can be improved through the adequate use of crossbreeding systems. End-product traits on the other hand are moderately to highly heritable benefit less from heterosis.

Optimal use of crossbreeding is more complex than simply mating a bull of breed A to a cow of breed B. If one, or both animals are “sub par”, heterosis cannot negate the inferiority of the parents. An effective crossbreeding program requires careful selection of breeds that compliment each other and then careful selection of parents within those respective breeds. Successful crossbreeding programs focus on optimums, not maximums or minimums, employing multiple breeds to achieve breeding objectives and marketing goals that fit the production environment.

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