Genetic effects for reproductive traits in beef cattle and predicted performance

Area of Science:

• Animal Science
• Genetics
• Reproductive Biology

Background:

• Rotational crossbreeding systems are utilized in beef cattle production to leverage heterosis and breed complementarity.
• Understanding the direct and maternal genetic effects of different breeds is crucial for optimizing reproductive performance.

Purpose of the Study:

• To estimate direct (Ig) and maternal (Mg) additive, and direct (Ih) and maternal (Mh) nonadditive genetic effects on reproductive traits in a four-breed rotational crossbreeding system.
• To evaluate the impact of Angus, Brahman, Charolais, and Hereford breeds on calving rate, calf survival, weaning rate, calving assistance, and calf birth date.

Main Methods:

• Collected reproductive data from 4,595 cow exposures and calvings over four generations.
• Estimated genetic effects by regressing individual animal response on expected breed proportions in offspring and dams.
• Expressed breed effects as deviations from the least squares mean.

Main Results:

• Brahman direct additive (Ig) effects reduced calving and weaning rates but maternal nonadditive (Mh) effects involving Brahman improved weaning rates.
• Brahman Ig effects delayed calf birth date, while Angus and Hereford Ig effects hastened it. Brahman combination Mh effects also influenced earlier birth dates.
• Charolais Ig effects increased calving assistance, whereas Angus-Brahman and Brahman-Charolais Mh effects reduced it, indicating more desirable outcomes.

Conclusions:

• Rotational crossbreeding systems yield reproductive trait predictions intermediate to two- and three-breed terminal crosses.
• Maximized calving and weaning rates are predicted with Brahman first-cross and Charolais-Hereford cows in three-breed cross mating systems.