|Rasby, Richard - UNIV OF NEBRASKA|
|Day, Michael - OHIO STATE UNIVERSITY|
|Johnson, Sandy - FORT HAYS STATE UNIV|
|Kinder, James - UNIV OF NEBRASKA|
|Lynch, J - HEARTLAND CATTLE COMPANY|
|Wettermann, Robert - OKLAHOMA STATE UNIV|
|Hafs, Harold - RUTGERS UNIVERSITY|
Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 18, 1998
Publication Date: N/A
Interpretive Summary: Many factors influence attainment of puberty in beef heifers. If puberty is not attained before the start of the breeding season, fertility and potential income to the cow/calf enterprise can be reduced. Treatments that induce puberty in heifers can potentially increase reproductive efficiency by allowing heifers to have already gone through their sub-fertile first estrus before the beginning of the breeding season. These heifers would then breed early in the breeding season, calve early in the calving season, and have greater weaning weights, and improved subsequent rebreeding performance. This research shows that puberty can be successfully induced in heifers. These treatments will give producers another option for managing replacement heifers.
Technical Abstract: The objectives of this experiment were to determine if treatment with progesterone (P4) using an intravaginal implant would induce estrus and cause development of corpora lutea (CL) with a typical life span and if treatment with estradiol benzoate (EB) following implant removal would enhance this response in peripubertal beef heifers. Peripubertal heifers (n=317) of European breeding at six locations were used in this experiment. Heifers received one of the following 3 treatments on day 0: 1) an intravaginal implant containing P4 for 7 days (P; n=103), 2) an intravaginal implant containing P4 for 7 days plus an injection of 1 mg of EB 24 to 30 hours after implant removal (PE; n=105), or 3) a sham implant for 7 days (C; n=109). Average weight and age of the heifers at the start of the trial were 292 +/- 45 kg and 365 +/- 38 days, respectively. P and PE treatment increased (P < .001) the proportion of heifers that were in estrus and formed normal CL after implant removal compared to control heifers. A greater (P < .0001) proportion of the heifers from the PE than P groups were in standing estrus (81% vs 37%) and formed normal CL (66% vs 44%) after implant removal. Of the heifers exhibiting estrus, a greater (P < .05) proportion of PE (94%) than P (80%) heifers were active between days 9 and 11. There was no difference among treatment groups in the proportion of heifers in standing estrus that formed a CL. Neither age, weight, nor body condition score interacted with treatment. Short term progesterone treatment increased the proportion of heifers in estrus and forming functional CL and adding EB to the progesterone treatment further enhanced the response.