Effect of interval from induction of puberty to initiation of a timed AI protocol on pregnancy rate in Nellore heifers

摘要

Prepubertal Bos indicus heifers (n = 774) were submitted to an E-2/P-4-based timed artificial insemination (TAI) protocol at three different intervals after induction of their pubertal ovulation by insertion of an intravaginal progesterone (P-4) device for 12 days. Heifers were randomly assigned to start the TAI protocol at 10 (group 10; n = 253), 12 (group 12; n = 265), or 14 (group 14; n = 256) days after the P4 device was removed. The TAI protocol consisted of the following: insertion of intravaginal device containing P4 (Controlled internal drug release [CIDR]; previously used twice for 9 days each) + estradiol benzoate (2 mg) on Day 0, CIDR withdrawal + estradiol cypionate (0.5 mg) and PGF2 alpha (12.5 mg) on Day 9, and TAI on Day 11. A subgroup of heifers (n = 472) was evaluated by ultrasound on Days 9 and 11 to evaluate the ovaries and to determine P4 concentrations on Day 9. On Day 9, more (P < 0.05) CLs were present, and follicular diameter was smaller (P < 0.05) for group 10 than for groups 12 and 14 (38.4%, 293%, and 23.3% with CL and 9.4 +/- 0.1, 9.9 +/- 0.1, and 9.8 +/- 0.1 mm diameter, respectively), but P4 concentrations did not differ (P > 0.1) between treatments (2.4 +/- 0.06 ng/mL). Follicular diameter at TAI (11.08 +/- 0.09 mm) and ovulation rate (88.4%) did not differ between treatments (P > 0.1). However, conception and pregnancy rates for all heifers were greater (P < 0.05) in group 12 (50.4% and 45.5%, respectively) than in group 10 (38.2% and 33.7%, respectively), with group 14 intermediate to other treatments (45.6% and 40.6%, respectively). The final pregnancy rate did not differ between treatments (80.9%). In conclusion, a 12-day interval from the end of the puberty induction protocol to the start of the TAI protocol resulted in greater conception and pregnancy rates in prepubertal Nellore heifers