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New insights into the influence of breed and time of the year on the response of ewes to the ‘ram effect’

Published online by Cambridge University Press:  27 May 2011

A. Chanvallon ,
L. Sagot ,
E. Pottier ,
N. Debus ,
D. François ,
T. Fassier ,
R. J. Scaramuzzi  and
C. Fabre-Nys
A. Chanvallon
Affiliation:
Centre Interrégional d'Information et de Recherche en Production Ovine, Site expérimental du Mourier, 87800 St Priest Ligoure, France UMR 6175 INRA Physiologie de la Reproduction et des Comportements – CNRS – Université de Tours – Haras Nationaux, 37380 Nouzilly, France
L. Sagot
Affiliation:
Institut de l'Elevage, 149 rue de Bercy, 75595 Paris Cedex 12, France
E. Pottier
Affiliation:
Centre Interrégional d'Information et de Recherche en Production Ovine, Site expérimental du Mourier, 87800 St Priest Ligoure, France Institut de l'Elevage, 149 rue de Bercy, 75595 Paris Cedex 12, France
N. Debus
Affiliation:
UMR868 “Elevage des Ruminants en Régions Chaudes”, 2 Place Viala, 34060 Montpellier Cedex 1, France
D. François
Affiliation:
INRA SAGA, Chemin de Borde-Rouge Auzeville, BP 52627, 31326 Castanet Tolosan, France
T. Fassier
Affiliation:
INRA Bourges, Domaine de la Sapinière, 18390 Osmoy, France
R. J. Scaramuzzi
Affiliation:
UMR 6175 INRA Physiologie de la Reproduction et des Comportements – CNRS – Université de Tours – Haras Nationaux, 37380 Nouzilly, France Department of Veterinary Basic Sciences, The Royal Veterinary College, Hawkshead Lane, North Mimms, Hertfordshire AL9 7TA, UK
C. Fabre-Nys*
Affiliation:
UMR 6175 INRA Physiologie de la Reproduction et des Comportements – CNRS – Université de Tours – Haras Nationaux, 37380 Nouzilly, France
*
†E-mail: fabre@tours.inra.fr
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Abstract

Exposure of anoestrous ewes to rams induces an increase in LH secretion, eventually leading to ovulation. This technique therefore is an effective, low-cost and hormone-free way of mating sheep outside the breeding season. However, the use of this technique is limited by the variability of the ewes’ responses. In this study, our objective was to understand more completely the origins of this variability and to determine the relative roles of breed, the point in time during anoestrus and the depth of anoestrus on the response to the ‘ram effect’. In the first experiment, the pattern of anoestrus on the basis of the concentration of progesterone determined weekly, was determined in four breeds including two less seasonal (Mérinos d'Arles and Romane), one highly seasonal (Mouton Vendéen) and one intermediate (Île-de-France) breeds. Anoestrus was longer and deeper in Mouton Vendéen and Île-de-France than in Romane or Mérinos d'Arles. In the second experiment, we used the same four breeds and tested their hypophyseal response to a challenge with a single dose of 75 ng gonadotrophin-releasing hormone (GnRH) in early, mid and late anoestrus, and then we examined their endocrine and ovarian responses to the ‘ram effect’. Most (97%) ewes responded to GnRH and most (93%) showed a short-term increase in LH pulsatility following the ‘ram effect’. The responses in both cases were higher in females that went on to ovulate, suggesting that the magnitude of the hypophyseal response to a GnRH challenge could be a predictor of the response to the ‘ram effect’. As previously observed, the best ovarian response was in Mérinos d'Arles at the end of anoestrus. However, there was no relationship between the proportion of females in the flock showing spontaneous ovulation and the response to the ‘ram effect’ of anoestrous ewes from the same flock.

Keywords

seasonalitysheepram effectanoestrusbreed
Type
Full Paper
Information
animal , Volume 5 , Issue 10 , 26 August 2011 , pp. 1594 - 1604
Copyright
Copyright © The Animal Consortium 2011

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