|Fike, Karol - UNIV OF NEBRASKA|
|Day, Michael - OHIO STATE UNIVERSITY|
|Inskeep, E - WEST VIRGINIA UNIVERSITY|
|Kinder, James - UNIV OF NEBRASKA|
|Lewis, Paul - WEST VIRGINIA UNIVERSITY|
|Hafs, Harold - RUTGERS UNIVERSITY|
Submitted to: Nebraska Beef Reports
Publication Type: Popular Publication
Publication Acceptance Date: November 1, 1998
Publication Date: N/A
Interpretive Summary: Initiation of estrous cycles in anestrous cows can potentially provide considerable economic benefit to cow-calf producers. Treatment of postpartum beef cows during lactational anestrus with progesterone and an injection of estradiol benzoate induced estrus and formation of a functional CL. These responses in anestrous cows can increase the percentage of cows exhibiting estrous cycles at the onset of the breeding season, which will result in more cows being maintained on a yearly calving interval and fewer cows being culled from the herd. Because these same treatments can be used to synchronize estrus in cows exhibiting estrous cycles, they provide the potential for artificial insemination of a large proportion of the herd at the same time.
Technical Abstract: Suckled anestrous beef cows (n=362) from 25 to 50 d postpartum were used to determine effects of progesterone (P4) alone or in combination with an injection of estradiol benzoate (EB) on percentage of cows that formed a corpus luteum (CL) and exhibited behavioral estrus. Four locations served as replicates. Cows within replicate were stratified by calving date and assigned to receive one of four treatments arranged in a 2x2 factorial. At treatment initiation (d 0), cows received either; 1) an intravaginal implant containing P4 for 7 d plus an injection of 1 mg of EB 24 to 30 h after implant removal (P4 + EB), 2) an intravaginal implant containing P4 for 7 d (P4), 3) a sham implant for 7 d plus an injection of 1 mg of EB 24 to 30 h after implant removal (EB), or 4) a sham implant for 7 d (Control). Progesterone treatment increased the proportion of cows that formed a fully functional CL (P<.0001) and exhibited behavioral estrus (P<.05). Treatment with EB following implant removal did not (P>.10) alter the proportion of cows that formed a fully functional CL but did increase (P<.001) the proportion of cows that exhibited behavioral estrus. Body condition score, parity, and number of days postpartum did not affect the proportions of cows (P>.10) that formed fully functional CL nor exhibited behavioral estrus, however, location affected (P<.05) the proportion of cows that exhibited behavioral estrus. Short-term treatment with P4 caused resumption of cyclic ovulatory activity in suckled-anestrous beef cows while EB enhanced the expression of estrus.