Resumen:
The objective of this randomized, controlled study was to evaluate the reproductive and economic performance of dairy Holstein heifers managed for first to third artificial inseminations (AIs) with or without an intravaginal progesterone device (IPD) under different temperature-humidity indexes (THI) and combined with AI after observed estrus. A total of 503 heifers from one rearing commercial farm were randomly assigned for first AI to the 5d Co-synch 72 h protocol (5dCO; n=261) or to the 5d Co-synch protocol plus IPD (5dCOP4; n=242). In a subset of heifers (n = 193) we determined progesterone (p4) and performed an ovarian ultrasound scanner on Days 0, 5, 8 and 15. Animals were considered to be synchronized on Day 5 if p4 > 1 ng/mL and a corpus luteum present; synchronized on Day 8 if p4 < 1 ng/mL, luteolysis and a follicle > 8 mm diameter was observed; and synchronized on Day 15 if p4 > 1 ng/mL and ovulation occurred, defined as the presence of a CL in the ovary where a follicle had been detected on Day 8. Pregnancy diagnosis was performed by ultrasound scanner on Days 28-35 after AI. The diagnosis confirmation was done by ultrasound on Days 50-56 and again on Days 100-113 after AI. Non-pregnan...