Abstract:
Variation in estrous response is a major concern in estrus synchronization programs using prostaglandin F2�. The objective of this study was to confine estrous detection within two phases (48 h each) after synchronizing follicular wave emergence using ovarian follicle regressing (first phase) and ovulating (second phase) agents. Cyclic Sistani cattle (Iranian Bos indicus beef breed) at unknown stages of the estrous cycle and e58 days open were randomly assigned to two groups in mid summer. Females received a ration comprised of wheat straw (39%), Lucerne hay (28%) and concentrate (33%) that comprised 10% crude protein and energy at 2.1 Mcal/kg DM, according to NRC recommendations for beef cattle. In phase one, females in Group 1 (n = 33; heifers: 9; lactating cows: 4; dry cows: 20; 59 � 5.8 months of age; 361.2 � 11.5 kg LW; and 2.1 � 0.41 lactations) received estradiol benzoate (2 mg, i.m., Aburaihan Pharmaceutical Co., Tehran, Iran) and progesterone (100 mg, i.m., Aburaihan, Iran) followed by an injection of prostaglandin analogue (15 mg, i.m., Prosolvin; Intervet, Boxmeer, The Netherlands) and PMSG (400 IU, i.m., Folligon; Intervet) on Day 8. Females in Group 2 (n = 35; heifers: 9; lactating cows: 5; dry cows: 21; 59.3 � 5.7 months of age; 356.8 � 11.5 kg LW; and 2 � 0.35 lactations) received two consecutive injections of prostaglandin 14 days apart. In the second phase, starting 72 h after prostaglandin injection, females in both groups that did not exhibit estrus were given an intra-muscular injection of Gonadorelin (100 �g, Fertagyl, Intervet) followed by prostaglandin injection 7 days later. In both phases, standing estrus was recorded for 48 h, after prostaglandin injection, at 4-h intervals, 30 min each time. Within a defined period (48 h after prostaglandin injection) 12 h after standing estrus, females were inseminated with frozen semen. Pregnancy was diagnosed on Day 30 after insemination using ultrasonography. Data were analyzed using logistic regression and chi-square tests. There was no significant effect of parity and lactation status on the frequency of estrus and conception rates (P > 0.05). The total frequency of observed standing estrus throughout two phases for Group 1 and two females were 81.8% and 80%, respectively (P > 0.05). The conception rates from a single AI for Group 1 [1st phase: 70.6% (12/17); 2nd phase: 40% (4/10); total: 59.2% (16/27)] did not differ (P > 0.05) to that for Group 2 [1st phase: 66.7% (8/12); 2nd phase: 56.2% (9/16); total: 60.7% (17/28)]. The result of this study demonstrated that estrous detection rates of e80% can be achieved within 4 day observation period in Bos indicus beef cattle.<fn_group><fn>The authors express their great appreciations to the Intervet Company, Holland and the Aburaihan Company, Iran, for kind provision of pharmaceutical materials to perform this experiment.</fn></fn_group>