Use of sex-sorted sperm in lactating dairy cows upon estrus detection or following timed artificial insemination

The present study evaluated the use of sex-sorted sperm upon estrus detection (ED) or following timed artificial insemination (TAI) in lactating dairy cows. Additionally, the effect of the presence of a corpus luteum (CL) at the beginning of the TAI protocol was verified. Cows (539 crossbred Gir × Holstein and 87 Holstein) were classified according to the presence or absence of CL by ultrasonography exam. Cows with a CL were randomly assigned into one of two groups (CL-ED/AI or CL-TAI), and cows without a CL (NoCL-TAI) received TAI. Cows from the CL-ED/AI group received 500 mg of cloprostenol intramuscularly and were inseminated 12 h after ED in the following five days. Cows from the TAI groups (CL or NoCL) received TAI. Cows receiving CL-ED/AI had a lower (P < 0.0001) service rate (45.1%, 101/224) than TAI groups (CL-TAI = 94.2%, 180/191 and NoCL-TAI = 97.2%, 205/211). However, cows receiving AI upon ED (CL-ED/AI = 31.7%, 32/101) presented higher (P = 0.03) pregnancy per AI (P/AI) than cows bred following TAI (CL-TAI = 19.4%, 35/180 and NoCL-TAI = 23.9%, 49/205). Despite the lower P/AI, cows receiving TAI presented greater (P = 0.07) proportion of pregnant cows at the end of the reproductive program (CL-TAI = 18.3%, 35/191 and NoCL-TAI = 23.2%, 49/211) than those inseminated upon ED (14.3%, 32/224). There was no effect (P = 0.45) of the presence of a CL at the beginning of the synchronization protocol on P/AI. Thus, the use of TAI programs, regardless of the presence of CL in the beginning of the synchronization protocol, increases the service and pregnancy rates but reduces the P/AI when compared to the use of sex-sorted sperm upon ED.