| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
University of Nebraska2, Lincoln 68583
Abstract
As experiment was conducted with 15 Angus x Hereford heifers that were 16 mo of age at the time the experiment was initiated. The heifers were assigned randomly in equal numbers to be fed low (L), maintenance (M) or high (H) energy diets for 191 d. Overall average weight for heifers at the time the experiment was initiated was 294 ± 6 kg. All heifers were exhibiting estrous cycles at regular intervals and estrus was synchronized using a progestogen implant (norgestomet) in combination with an injection of estradiol valerate and norgestomet before initiation of dietary treatments. Dietary treatments started at time of implant removal and this day was designated as d 0. Blood samples were collected every other day from d 150 to 160 and progesterone concentrations were quantified to evaluate estrous cycle activity. In order to resynchronize the reproductive state, all heifers were retreated with norgestomet implants and injected with the estradiol valerate and norgestomet combination on d 160. Implants were removed on d 170. Serial blood samples were collected for 4-h periods at 20-min intervals starting at 0, 10, 20 and 30 h after implant removal and luteinizing hormone (LH) concentrations were quantified. Progesterone was quantified in samples collected at daily intervals (170 to 191 d) to evaluate whether a normal estrous cycle occurred subsequent to removal of the implant. Four of five heifers in each of the L and M treatment groups were not cycling, whereas all heifers in the H treatment were cycling at the time of progestogen implantation on d 160. All but one of the 15 heifers showed signs of behavioral estrus within 72 h after removal of the implant. One, two and five of the five heifers fed the L, M and H diets, respectively, had normal estrous cycles subsequent to implant removal. Treatment influenced mean serum LH concentrations (P<.01) and frequency of LH pulses (P<.01). Mean LH concentration was also affected (P<.01) by sampling period subsequent to implant removal. Mean LH concentrations were higher in heifers fed the H diet than in heifers fed the L and M diets during the first three serial collection periods (P<.01). Frequency of LH pulses was higher during the first three periods of serial blood collection in H- than M- and L-treated heifers (P<.05). Low circulating concentrations of LH and lack of pulsatile secretion could partially explain why anestrous heifers failed to initiate estrous cycles after treatment with the norgestomet-estradiol valerate combination.
1 Published as Paper No. 7002, Journal Ser. Nebraska Agr. Exp. Sta.
2 Anirn. Sci. Dept. Acknowledgement is made to Jane A. Ossenkop and Diana J. Smith for assistance in preparation of the manuscript, to John C. Fudge, Douglas Zalesky and Duane Reese for assistance in data collection, to Dennis R. Brink for assistance in preparation of diets, to Kenneth A. Pearson for technical assistance in laboratory procedures and to Stephen R. Lowry and Merlyn K. Nielsen for assistance in analysis of data
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
