Opioidergic and nutritional involvement in the control of luteinizing hormone secretion of postpartum Rasa Aragonesa ewes lambing in the mid-breeding season |
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| Affiliation: | 1. College of Science, Health, Engineering and Education, Murdoch University, 90 South Street, Murdoch, WA, 6150, Australia;2. Massey University, Palmerston North, 4410, New Zealand;3. New South Wales Department of Primary Industries, Cowra Agricultural Research and Advisory Station, Cowra, NSW, 2794, Australia;4. School of Agriculture and Environment, M085, University of Western Australia, 35 Stirling Hwy, Crawley, WA, 6009, Australia;1. Vertebrate Biology and Conservation Group, University Complutense of Madrid, E-28049 Madrid, Spain;2. Deputy General Directorate on Nature, Spanish Ministry of Agriculture, Food and Environment, E-28071 Madrid, Spain;3. Bearded Vulture Study and Protection Group, Apdo. 45, E-25520 El Pont de Suert, Spain;4. FOMECAM S. L. Aragón 43, E-13004 Ciudad Real, Spain;5. Department of Animal Production (Division of Wildlife), Faculty of Life Sciences and Engineering, University of Lleida, E-25198 Lleida, Spain;6. Division of Conservation Biology, Institute of Ecology and Evolution, University of Bern, CH-3012 Bern, Switzerland;2. Dairy Science Department, South Dakota State University, Brookings 57007;1. Facultad de Ciencias Marinas, Universidad Autónoma de Baja California, Carretera Ensenada-Tijuana 3917, Fraccionamiento Playitas, 22860, Ensenada, BC, Mexico;2. Investigación y Conservación de Mamíferos Marinos de Ensenada, A.C. Colinas Popotla 356, Colinas del mar, 22760, Ensenada, BC, Mexico;3. Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Carretera Ensenada-Tijuana 3917, Fraccionamiento Playitas, 22860, Ensenada, BC, Mexico;4. Departamento de Biología de la Conservación, Centro de Investigación Científica y de Educación Superior de Ensenada, Carretera Tijuana-Ensenada 3918, Zona Playitas, 22860, Ensenada, BC, Mexico |
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| Abstract: | The role of endogenous opioids and nutrition on the inhibition of luteinizing hormone (LH) secretion during the postpartum period was investigated in a Spanish breed of sheep lambing in the mid-late breeding season. Two groups of adult Rasa Aragonesa ewes housed in individual pens and lambing on 30 December were fed during the suckling period to provide maintenance requirements and the production of 1.1 (M; n=8) or 0.55 (L; n=8) kg of milk per day. On days 10, 20 and 30 after lambing, the effect of a treatment with the opiate receptor antagonist naloxone (1 mg/kg at four hourly intervals) on LH secretion was assessed in half of the ewes of each group, the remaining females receiving four saline injections. After weaning, animals were fed to provide requirements for maintenance of liveweight. Blood samples were collected twice a week from day 20 postpartum until the end of March, and assayed for progesterone and prolactin. Although underfed ewes showed significantly lower mean plasma concentrations during the control period on day 20 postpartum, nutrition did not seem to modify LH secretion before naloxone or saline injections. Moreover, no differences between nutritional groups in the response to naloxone injections on pattern of LH secretion were found. In fact, naloxone treatment induced an increase of mean LH concentrations on days 10, 20 and 30 postpartum (at least, P<0.05), of LH pulse frequency on days 20 and 30 (P<0.05), and of LH pulse amplitude on days 10 and 20 (P<0.05). Underfed ewes during the postpartum period showed a slower decline in plasma prolactin levels, with significant differences on days 29, 36 and 39 after lambing (P<0.05). Only 3 M ewes ovulated before the onset of the seasonal anoestrus period. It is concluded that endogenous opioids are involved in the inhibition of LH secretion during the early suckling period of a reduced seasonality breed of sheep without any influence of nutrition on the response to naloxone treatment; however, ewes underfed before weaning failed to reactivate their cyclicity prior to the onset of the seasonal anoestrus. |
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