Presynchronization with prostaglandin F2 and prolonged exposure to exogenous progesterone impacts estrus expression and fertility in beef heifers.
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abstract
To determine the effects of two presynchronization strategies in conjunction with delayed fixed-time artificial insemination (TAI) on pregnancy rates to TAI (PR/AI), 1700 Angus beef heifers at three locations in South Dakota were enrolled in a completely randomized design with a 2 by 2 factorial arrangement of treatments. Within location, all heifers were randomly assigned to one of four treatments: 1) PG54 (n=434), heifers were administered prostaglandin F2 (PGF; 25mg im) 7d prior [Day-14] to the initiation of the 7-d CO-Synch+controlled internal drug releasing (CIDR) protocol wherein they received gonadotropin-releasing hormone (GnRH; 100g im) and a CIDR insert on Day-7, PGF at CIDR removal on Day 0, and a second injection of GnRH concurrently with TAI 542h later; 2) PG72 (n=426), heifers were exposed to the same treatment as PG54, however, TAI was performed 722h after CIDR removal; 3) PG-CIDR54 (n=422), same as PG54 but heifers received a CIDR insert on Day-14 rather than Day-7, in addition to PGF administration; 4) PG-CIDR72 (n=418), same as PG-CIDR54, however, TAI was performed 722h after CIDR removal. Estrus detection patches were applied to all heifers on Day 0 and were evaluated for activation at TAI. Pregnancy was diagnosed via transrectal ultrasonography between 30 and 47d after TAI. The percentage of heifers exhibiting estrus between Day 0 and TAI was greater (P<0.01) in the PG72, PG-CIDR54, and PG-CIDR72 treatments compared to the PG54 treatment (78.11, 86.59, and 91.09 vs. 31.05%, respectively). Furthermore, estrus response was greater (P<0.01) in PG-CIDR72 heifers when compared to PG72. Pregnancy rates to TAI differed among treatments and were greater (P<0.05) in the PG72 and PG-CIDR54 treatments when compared to PG-CIDR72 (48.8 and 50.4 vs. 38.4%, respectively), and were greater (P=0.03) in PG-CIDR54 vs. PG54 (43.1%). Moreover, a tendency (P=0.10) was determined on PR/AI between PG54 and PG72. In conclusion, presynchronization strategies and prolonged exposure to exogenous progesterone have the potential to alter estrus expression and improve fertility in replacement beef heifers.
