H. D. Norman1 and J. L. Hutchison
Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350
2009 J. Dairy Sci. (?)
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To determine the effect of sexed-semen use on heifer and cow conception rate, records were examined for 1.3 million heifer and 10.8 million cow breedings of Holsteins in US Dairy Herd Improvement herds from 2006 through 2008. Of those records, 25% included data on calf sex, dystocia and stillbirth for heifer breedings, 12% included data on calf sex and dystocia for cow breedings, and 9% included data on stillbirth for cow breedings. Heifer and cow breedings were analyzed separately for fixed effect of breeding year, parity (for cows), service number, semen type (conventional or sexed), and calf sex (for dystocia and stillbirth) on conception rate, calf sex, dystocia, and stillbirth. Statistical differences were determined by chi square test. Mean conception rates for heifers were 56% for conventional semen and 39% for sexed semen; corresponding conception rates for cows were 30 and 25%. Difference between conception rates for sexed-semen and conventional-semen breedings declined 14 to 20 percentage units as service number increased for heifers and 4 to 10 percentage points as service number and parity increased for cows. For single births, sexed-semen breedings resulted in a high percentage of female calves (91% for heifers and 89% for cows). Dystocia and stillbirth were more frequent for heifers (6 and 10%, respectively, for conventional semen; 4 and 11% for sexed semen) than for cows (3 and 4% for conventional semen; 1 and 3% for sexed semen). Because sexed semen use greatly increased the percentage of female calves, the percentage of difficult births was reduced by 28% for heifers and 63% for cows. Stillbirths were more prevalent for twin births with the exception of sexed-semen heifer breedings, most likely a result of lower dystocia associated with female calves. The incidence of stillbirths among heifers with single male calves was higher from sexed-semen breedings (16%) than from conventional semen (11%); however, a corresponding difference was not observed for cows. Stillbirth frequency was reduced by sexed-semen use for cows but not for heifers.
(Key words: sexed semen, conception rate, dystocia, stillbirth)