Genetic Relationships Between Male and Female Reproductive Traits in Beef Cattle

Reproductive traits were measured for 234 bulls and 1184 heifers from matings of three dam breeds (Angus, Hereford, and MARC III) with six sire breeds (Angus, Hereford, Brahman, Boran, Tuli, and Belgian Blue) from the Germ Plasm Evaluation (GPE) Program at Roman L. Hruska US Meat Animal Research Center. Male traits were yearling scrotal circumference (YSC), height (YH), and yearling BW; age at puberty (AP1; production of 50 million sperm with ≥10% progressive motility); age, scrotal circumference, average testis length, and testicular volume when 500 million sperm were produced with ≥50% progressive motility (AP3, SC3, L3 and V3, respectively); and 15-mo BW (15W) and height (15H). Traits of females were age at puberty (AP, first estrus) and pregnancy rate (PR) at 18 mo. The objective was to determine whether indirect selection on male traits would be effective for improving female fertility traits. Selection of males on AP1, AP3, SC3, L3, V3, YH, 15W, and 15H may be useful for 1Published as paper no. 14841, Journal Series, Nebraska Agric. Res. Div., Univ. of Nebraska, Lincoln 68583-0908. 2Current address: University of Nebraska, Lincoln 68583-0908. 3To whom correspondence should be addressed: [email protected] improving PR because of genetic correlations and low heritability for PR. Although no male trait was found to be effective for improving AP in females through indirect selection, YSC and SC3 were the most favorable. If heritability were as large as estimated in this study for AP (0.52), direct rather than indirect selection would seem to be more effective for AP in heifers, although the difficulty of measuring AP in heifers also would need to be considered. Male reproductive traits, such as scrotal circumference and also YH and 15H, however, are easier and less expensive to measure than female reproductive traits, and greater selection intensity can be applied to these male traits. (