Abstract
Aim:This study was designed to evaluate the effect of gonadotropin-releasing hormone (GnRH), human chorionic gonadotropin (hCG), and progesterone impregnated intra-vaginal device on progesterone profile and conception rate in repeat-breeding crossbred cows.Materials and Methods:Repeat-breeding crossbred cows aged 3-8 years (n=32), lactating and negative to white side test were randomly divided into four groups: Group 1 (Control, n=8), Group 2 (GnRH at 10 µg i.m, n=8), Group 3 (hCG at 1500 IU i.m., n=8), and Group 4 (progesterone impregnated intra-vaginal device at 958 mg, n=8). All the treatme nts were given on 5th daypostbreeding and in Group 4 intra-vaginally implanted device was withdrawn on 9th day (i.e., implant inserted for total 4 days) of the estrous cycle. Blood samples were collected on day 0, 5, 10, 15, and day 20 of estrous cycle, and plasma was separated for progesterone estimation.Results:Accessory corpus luteum was not formed in crossbred cows of Group4 and control group. However, total 6 and 8 accessory corpora lutea were found in Group 2 and Group 3, respectively. In pregnant cows, the plasma progesterone concentration increased continuously from day 0 to day 20. In non-pregnant cows, it increased from day 0 to day 15 and then declined. The conception rate on day 60 in Group 1, Group 2, Group 3, and Group 4 was 37.5%, 50%, 75%, and 37.5%, respectively.Conclusions:Treating repeat-breeder cows with hCG is effective in increasing conception rate by developing accessory corpora lutea and higher progesterone level.
Highlights
Over the past five decades, the milk production increased while the pregnancy rate in dairy cows rapidly decreased [1] due to changes in reproductive physiology [2], resulting in increased number of services per conception [3]
All the treatme nts were given on 5th daypostbreeding and in Group 4 intra-vaginally implanted device was withdrawn on 9th day of the estrous cycle
Treating repeat-breeder cows with human chorionic gonadotropin (hCG) is effective in increasing conception rate by developing accessory corpora lutea and higher progesterone level
Summary
Over the past five decades, the milk production increased while the pregnancy rate in dairy cows rapidly decreased [1] due to changes in reproductive physiology [2], resulting in increased number of services per conception [3]. The repeat-breeding cow is one that has normal or nearly normal estrous cycles and estrous periods and has been bred 2 or more times to a fertile bull yet failed to conceive. The Creative Commons Public Domain Dedication waiver (http:// creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated
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