373 STRATEGIES TO IMPROVE CONCEPTION RATES IN DAIRY HEIFERS INDENTIFIED IN ESTRUS USING TAIL HEAD PAINTING AND INSEMINATED WITH SEXED SEMEN

Abstract

Two strategies to improve the conception rates in dairy heifers identified in estrus using tail head painting and inseminated with sexed semen were evaluated. In the first trial, the effect of GnRH injection (100 μg of gonadorelin) at estrus on ovarian responses and conception rates (CR) were verified. A total of 413 virgin Jersey heifers 11 to 12 mo of age were used. All heifers were treated with 25 mg of dinoprost tromethamine at the first day of the AI program. All inseminations were performed 12 h after estrus detection using sexed semen (2.1 million sperm) and the estrus was detected based upon removal of tail-head paint. At estrus detection, heifers were randomly assigned to receive GnRH or not (GnRH = 212 and No GnRH = 201). A subset of heifers (GnRH = 70 and No GnRH = 70), was scanned by ultrasound every 12 h after estrus detection until ovulation. The largest follicle diameter at estrus (LF), ovulatory follicular diameter (OF), ovulation rate (OR), interval between beginning of estrus and ovulation (IEO), and the proportion of heifers presenting late ovulation (LO, ovulation occurred with more than 36 h after the beginning of estrus) were recorded. The GnRH did not influence the LF (13.3 ± 0.9 v. 13.4 ± 0.2 mm; P = 0.87), the OF (13.4 ± 0.3 v. 13.9 ± 0.2 mm; P = 0.17), or OR [98.6% (69/70) v. 97.1% (68/70); P = 0.57]. However, GnRH treatment tended to shorten the IEO (29.2 ± 1.1 h v. 32.0 ± 1.3 h; P = 0.07) and reduced the occurrence of LO (2.9% (2/69) v. 16.2% (11/68); P = 0.02). However, GnRH injection did not influence the CR [GnRH = 47.2% (100/212) v. No GnRH = 51.7% (104/201); P = 0.38]. The second trial evaluated the CRin dairy heifers after the use of single or double insemination dose. A total of 576 Jersey heifers receiving first, second, or third insemination services were used. The heifers were assigned according to sire utilized into one of the three groups (Single 12 h, Double 12 h, or Double 12/24 h). In Single 12 h (n = 193) or Double 12 h (n = 193) groups, heifers received one or two insemination doses (2.1 million sperm) of sexed semen 12 h after estrus detection, respectively. The Double 12/24 h (n = 190) group heifers received two doses 12 h apart from each other (first dose at 12 h and second dose at 24 h after estrus detection). Differences were found between the number of AI services (P = 0.004) on the CR [First = 55.3%a (115/208); Second = 46.1%a (94/204); Third = 34.8% (57/165); P = 0.004]. However, there was no effect of treatment on the CR [Single 12 h = 45.1% (87/193); Double 12 h = 44.0% (85/193); Double 12/24 h = 49.5% (94/190); P = 0.51]. In conclusion, the GnRH injection altered the timing of ovulation, but failed to increase the CR. Furthermore, double insemination doses of sexed semen did not influence the CR in dairy heifers.

Dalhart Jersey Ranch-TX, USA and Sexing Technologies-SP, Brazil.