The use of sexed semen (SS) for AI of cattle has resulted in lower pregnancy per timed AI (P/TAI) compared with conventional semen. This has been attributed to lower sperm dose and cell damage during the cell sorting-freezing process. Horn AI is a common practice in equines and canines to improve pregnancy rate when using low sperm doses. The objective was to compare P/TAI and pregnancy loss (PL) in dairy heifers inseminated with SS deposited in the uterine horn (UH) ipsilateral to the ovary containing the preovulatory follicle (POF) versus TAI in the uterine body (UB). This study was performed on two dairy farms in Georgia (A and B). On farm A, 74 Holstein heifers (12 months old) received a 5-day Cosynch + controlled internal drug release (CIDR) protocol including an intravaginal insert (Eazi-Breed CIDR, Zoetis Animal Health) containing 1.38g of progesterone for 5 days and a dose of gonadotrophin-releasing hormone (GnRH) intramuscularly (100µg, 2mL of Factrel, Zoetis Animal Health). At CIDR removal, heifers received a dose of prostaglandin F2α (PGF2α) intramuscularly (25mg, 5mL of Lutalyse, Zoetis Animal Health) and again 24h later; 72h after CIDR removal, heifers received 100µg of GnRH intramuscularly and TAI with frozen-thawed SS. On farm B, 237 Holstein×Jersey heifers (12 months old) received a modified 5-day Cosynch + CIDR. This protocol was similar to that on farm A but did not include GnRH at the time of CIDR insertion or a second dose of PGF2α 24h after CIDR removal. Immediately before TAI, heifers were examined using transrectal ultrasonography (TRUS) to determine on which ovary the POF was present. Each heifer was randomly assigned to TAI using SS in either the UH ipsilateral to the ovary containing the POF (n=150; farm A, n=32; farm B, n=118) or the UB regardless of where the POF was identified (n=161; farm A, n=42; farm B, n=119). Pregnancy was diagnosed 32 days after TAI using TRUS to determine P/TAI. Heifers diagnosed pregnant were re-examined using TRUS at 60 days of gestation to assess PL. Data were analysed using PROC LOGISTIC and the chi-square test of SAS (SAS Institute Inc.). Heifers that received SS in the UH had adequate P/TAI (50.6% (76/150); farm A: 50.0% (16/32); farm B: 50.8% (60/118)), which tended to be numerically greater (P=0.12) than that observed in heifers receiving SS in the UB (43.4% (70/161); farm A: 40.5% (17/42); farm B: 44.5% (53/119)). In addition, PL was not different between groups and was within normal ranges for dairy heifers (10.0 and 9.4% for UH and UB, respectively). In conclusion, TAI of dairy heifers with SS deposited in the UH ipsilateral to the ovary containing the POF resulted in adequate P/TAI, which was 7.2% greater than TAI in the UB. Horn AI with SS might become a valuable tool for optimising reproductive efficiency and genetic selection of dairy herds.
The Economics of Sexed Semen in Dairy Heifers and Cows