Incorporation of sexed semen into reproductive management of cow–calf operations

Abstract

The objective of this experiment was to compare reproductive performance and weaning outcomes of beef cows inseminated with sexed or conventional semen. Over 2 consecutive years, lactating Angus×Hereford cows were assigned to an estrus synchronization+artificial insemination (AI) protocol. At the time of AI, cows were ranked by parity and assigned to be inseminated with conventional non-sorted semen (CONV; n=454) or with semen sorted for male sperm (SEXED; n=439). Beginning 18 days after AI, cows from both treatments were grouped and exposed to mature bulls for 50 days (1:25 bull to cow ratio). Cow pregnancy status to AI was verified by detecting a fetus via transrectal ultrasonography 40 days after AI. Calf birth date, sex, and birth BW were recorded during the subsequent calving season. Cows that were diagnosed as pregnant during the transrectal ultrasonography exam and gave birth during the initial 2 weeks of the calving season were considered pregnant to AI. Pregnancy rates to AI and final pregnancy rates (AI+bull breeding) were reduced (P≤0.05) in SEXED compared with CONV cows. The proportion of male calves born to AI or AI+bull breeding was greater (P<0.01) in SEXED compared with CONV cows. No treatment effect was detected (P=0.34) for weaning rate, whereas SEXED cows had a greater (P<0.01) proportion of steers in the weaned calf crop compared with CONV cows. Steers and heifers from SEXED cows were younger (P<0.01), whereas only SEXED heifers were lighter (P=0.05) at weaning compared with cohorts from CONV cows. Across genders, calves from SEXED cows had reduced (P≤0.01) weaning age and BW compared with calves from CONV cows. Cows assigned to SEXED had greater (P=0.05) kg of steer weaned/cow exposed to breeding, but reduced kg of heifer weaned/cow exposed to breeding (P<0.01) compared with CONV cows. Across genders, SEXED cows tended (P=0.09) to have reduced kg of calf weaned/cow exposed to breeding compared with CONV cows. In summary, inseminating beef cows with sexed semen reduced pregnancy rates, but increased the proportion of steers weaned and kg of steers weaned/cow exposed to breeding. However, overall kg of calf weaned/cow exposed to breeding was not improved by the use of sexed semen, particularly because of its negative impacts on weaning age and BW of the heifer progeny.