Effect of GnRH pretreatment on reproductive performance of postpartum suckled beef cows following synchronization of estrus using GnRH and PGF2alpha.

Abstract

The effect of GnRH pretreatment on estrus detection rate, precision of estrus, and reproductive performance of postpartum beef cows synchronized to estrus using GnRH and PGF2alpha was evaluated. In Exp. 1, Angus cows (n = 87) were randomly assigned by parity, postpartum interval, and body condition score (BCS) to receive either 1) GnRH on d -7 and PGF2alpha on d 0 (GP) or 2) the GP treatment and an additional injection of GnRH on d -16 (GGP). Estrus detection and AI were conducted twice daily from d -3 to d 3. At 72 h after PGF2alpha, all animals not previously detected in estrus were bred by AI and received a concurrent injection of GnRH (TAI). Synchronized pregnancy rates were numerically increased (P = 0.15) in cows treated with GGP (55%) compared with those on the GP treatment (44%). In Exp. 2, 1,276 spring-calving, suckled beef cows in nine herds were randomized to treatments as described for Exp. 1, except that the initial GnRH injection for the GGP treatment was administered on d -14. Herd affected all indicators of reproductive performance (P < 0.05). The percentage of animals detected in estrus prematurely (d -3 to d 0; 7%) was not affected by treatment. Estrus response rate was influenced by postpartum interval (< 60 vs > or = 60; 61 vs 73%; P < 0.01) and a three-way interaction of parity, BCS, and treatment (P < 0.01). Within animals with a BCS > or = 5.5, the GGP treatment tended to increase the detection of estrus in primiparous cows (GP vs GGP; 76 vs 91%; P = 0.11) and decrease detection in multiparous cows (GP vs GGP; 78 vs 72%; P< 0.10). However, because conception rate to TAI in animals with a BCS > or = 5.5 was greater (P < 0.05) in the GGP than in the GP group (28 vs 8%, respectively), this interaction was interpreted to represent a shift in interval to estrus induced by the GGP treatment, rather than a reduction in the synchronization of ovarian function. Conception rates of animals inseminated to an observed estrus did not differ among treatments (P = 0.15). Synchronized pregnancy rate tended (P = 0.06) to be greater in GGP- (53%) than in GP-treated animals (47%). In conclusion, pretreatment with GnRH tended to increase pregnancy rates during a 6-d synchronization period, primarily through enhanced conception rates of cows bred by TAI. In contrast to our hypothesis, GnRH pretreatment did not increase the percentage of animals detected in estrus or the precision of estrus expression.

Pregnancy Rates in Lactating Dairy Cows After Presynchronization of Estrous Cycles and Variations of the Ovsynch Protocol

“…Moreover, recent studies in lactating beef cattle (Stevenson et al, 2000;DeJarnette et al, 2001a) and lactating dairy cows (Badinga et al, 1994) reported that the time of estrus after GnRH + PGF 2α treatment was approximately 60 h after PGF 2α . In another study, DeJarnette and Marshall (2003) reported that 65% of lactating dairy cows that were presynchronized with 2 PGF 2α injections (14 d apart) showed estrus on d 3 after the PGF 2α injection of Ovsynch, whereas none was observed in estrus before PGF 2α .…”

Sincronización del estro con PGF2&#945; y conducta estrual en vacas Criollo Lechero Tropical

“…La tasa de ME en respuesta a la PGF 2α fue 67%, inferior a la señalada en vacas Holstein (76 a 89%; Ryan et al, 1995) y mayor a la obtenida en Angus (44%; DeJarnette et al, 2001). La ausencia de ME en algunas vacas podría atribuirse a que la PGF 2α no se aplicó en el momento óptimo para la luteólisis, la jerarquía social en el hato, calores silenciosos o fallas en DVE.…”

Pregnancy Rates in Angus Cross Beef Cows Bred at Observed Oestrus With or Without Second GnRH Administration in Fixed‐Time Progesterone‐Supplemented Ovsynch and CO‐Synch Protocols

“…Observation of oestrus and insemination requires labour and cows with synchronized oestrous cycles may exhibit oestrus prior to fixed‐time breeding associated with the protocol. Studies have reported that up to 72% of cows exhibit oestrus prior to or immediately after the PGF 2α administration (DeJarnette et al. 2001; Larson et al.…”