Influence of perioestrous suprabasal progesterone levels on cycle length,oestrous behaviour and ovulation in heifers |
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| Affiliation: | 1. Department of Obstetrics and Gynaecology, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden;2. Swedish Association for Livestock Breeding and Production, S-631 84 Eskilstuna, Sweden;3. Department of Clinical Chemistry, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden;1. CIISA, Faculty of Veterinary Medicine, University of Lisbon, Lisbon, Portugal;2. Department of Animal Science, Coimbra College of Agriculture, Coimbra, Portugal;3. Department of Reproductive Immunology and Pathology, Institute of Animal Reproduction and Food Research of PAS, Olsztyn, Poland;1. Department of Animal Science, Campus of Agriculture and Natural Resources, University of Tehran, Karaj, Tehran 31587-77871, Iran;2. Department of Animal Sciences, College of Agriculture, Isfahan University of Technology, Isfahan 84156–83111, Iran;1. Physiology and Climatology, Indian Veterinary Research Institute, Izatnagar, Bareilly, Uttar Pradesh, India;2. Department of Animal Sciences and D.H. Barron Reproductive and Perinatal Biology Research Program, University of Florida, Gainesville, USA;1. Department of Production Animal Studies, Faculty of Veterinary Science, University of Pretoria, South Africa;2. Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, South Africa;3. Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, South Africa;4. Pferdezentrum Bad Saarow, Clinic for Horses, Free University, Bad Saarow, Germany;5. Department of Companion Animal Studies, Faculty of Veterinary Science, University of Pretoria, South Africa |
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| Abstract: | In order to induce suprabasal plasma concentrations of progesterone after luteolysis and to determine their effect on oestrous behaviour and ovulation, heifers subcutaneously received silicone implants containing 2.5 (n = 4), 5 (n = 4), 6 (n = 3), 7.5 (n = 3) or 10 (n = 4) g of progesterone, or an empty implant (controls, n = 5) between days 8 and 25 of the cycle (ovulation designated Day 0). Growth of dominant follicles and time of ovulation were determined by ultrasound, and signs of oestrus were recorded and scored. Blood was collected at 2–4 h intervals from Days 15 to 27 and assayed for progesterone concentration. In all heifers, plasma concentrations of progesterone sharply decreased during Days 16–18. Control heifers had their lowest progesterone levels on Days 20.5 and 21, standing oestrus on Day 19.5 ± 0.4 (mean ± SEM), and ovulated on Day 20.7 ± 0.4. A similar pattern was observed in heifers treated with 2.5 and 5 g progesterone. Heifers treated with 6, 7.5 and 10 g of progesterone showed an extended (P < 0.05) interovulatory interval. Onset of prooestrus and time of maximum expression of signs of oestrus were not significantly different from those in controls. However, there was an absence of standing oestrus in most of the cases, signs of oestrus lasted longer (P < 0.05) and were weaker in intensity when doses increased. In these groups, the lowest progesterone concentrations were attained shortly after implant removal. Some heifers treated with 6 and 7.5 g of progesterone had standing oestrus and post oestrous bleeding as seen in the controls but ovulation occurred from Days 24.5 to 27. When plasma progesterone concentrations were over 1 nmol 1−1, disturbed oestrus and delayed ovulation occurred. The extended period of prooestrus and oestrus and delayed ovulation were similar to that described in cases of repeat breeding. It is suggested that suprabasal plasma concentrations of progesterone, after luteolysis, may lead to asynchrony between onset of oestrus and ovulation and consequently be a cause of repeat breeding in cattle. |
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