The "Ram Effect": A "Non-Classical" Mechanism for Inducing LH Surges in Sheep

During spring sheep do not normally ovulate but exposure to a ram can induce ovulation. In some ewes an LH surge is induced immediately after exposure to a ram thus raising questions about the control of this precocious LH surge. Our first aim was to determine the plasma concentrations of oestradiol (E2) E2 in anoestrous ewes before and after the "ram effect" in ewes that had a "precocious" LH surge (starting within 6 hours), a "normal" surge (between 6 and 28h) and "late» surge (not detected by 56h). In another experiment we tested if a small increase in circulating E2 could induce an LH surge in anoestrus ewes. The concentration of E2 significantly was not different at the time of ram introduction among ewes with the three types of LH surge. "Precocious" LH surges were not preceded by a large increase in E2 unlike "normal" surges and small elevations of circulating E2 alone were unable to induce LH surges. These results show that the "precocious" LH surge was not the result of E2 positive feedback. Our second aim was to test if noradrenaline (NA) is involved in the LH response to the "ram effect". Using double labelling for Fos and tyrosine hydroxylase (TH) we showed that exposure of anoestrous ewes to a ram induced a higher density of cells positive for both in the A1 nucleus and the Locus Coeruleus complex compared to unstimulated controls. Finally, the administration by retrodialysis into the preoptic area, of NA increased the proportion of ewes with an LH response to ram odor whereas treatment with the α1 antagonist Prazosin decreased the LH pulse frequency and amplitude induced by a sexually active ram. Collectively these results suggest that in anoestrous ewes NA is involved in ram-induced LH secretion as observed in other induced ovulators

Evaluation of a commercial intravaginal thermometer to predict calving in a Hungarian Holstein‐Friesian dairy farm

In this study, the utility of a commercial intravaginal thermometer was evaluated as an automated method for the prediction of calving in a total of 257 healthy pregnant Holstein–Friesian female cattle. The accuracy and the sensitivity of predicting calving within 48 hr before calving were also evaluated. The intravaginal temperature changes from 72 hr before and up to calving were significantly (p ≤ .001) affected by parity, season (summer vs. autumn), the time of day (8 a.m. or 8 p.m.) and the 6-hr time intervals (38.19°C: first interval 0 to 6 hr before calving vs. 38.78°C: twelfth interval 66 to 72 hr before calving), while the gender (p = .943), and the weight of the calf (p = .610), twinning (p = .300), gestation length (p = .186), foetal presentation (p = .123), dystocia (p = .197) and retention of foetal membranes (p = .253) did not affect it significantly. The sensitivity of the SMS of expecting calving within 48 hr and the positive predictive value were 62.4% and 75%, respectively, while the sensitivity and the positive predictive value for the SMS of expulsion reached 100%. It can be concluded that the investigated thermometer is not able to predict calving within 48 hr accurately; however, imminent calving can be accurately alerted

Kisspeptin signaling is required for the luteinizing hormone response in anestrous ewes following the introduction of males

The introduction of a novel male stimulates the hypothalamic-pituitary-gonadal axis of female sheep during seasonal anestrus, leading to the resumption of follicle maturation and ovulation. How this pheromone cue activates pulsatile secretion of gonadotropin releasing hormone (GnRH)/luteinizing hormone (LH) is unknown. We hypothesised that pheromones activate kisspeptin neurons, the product of which is critical for the stimulation of GnRH neurons and fertility. During the non-breeding season, female sheep were exposed to novel males and blood samples collected for analysis of plasma LH profiles. Females without exposure to males served as controls. In addition, one hour before male exposure, a kisspeptin antagonist (P-271) or vehicle was infused into the lateral ventricle and continued for the entire period of male exposure. Introduction of a male led to elevated mean LH levels, due to increased LH pulse amplitude and pulse frequency in females, when compared to females not exposed to a male. Infusion of P-271 abolished this effect of male exposure. Brains were collected after the male effect stimulus and we observed an increase in the percentage of kisspeptin neurons co-expressing Fos, by immunohistochemistry. In addition, the per-cell expression of Kiss1 mRNA was increased in the rostral and mid (but not the caudal) arcuate nucleus (ARC) after male exposure in both aCSF and P-271 treated ewes, but the per-cell content of neurokinin B mRNA was decreased. There was also a generalized increase in Fos positive cells in the rostral and mid ARC as well as the ventromedial hypothalamus of females exposed to males. We conclude that introduction of male sheep to seasonally anestrous female sheep activates kisspeptin neurons and other cells in the hypothalamus, leading to increased GnRH/LH secretion

Early sexual experience and stressful conditions affect the response of young ewes to the male

 Exposure of anoestrous ewes to rams induces oestrous cycles (the 'ram effect'). This response is poor in young-sexually naive females, possibly because they lack sexual experience and are sensitive to stress. Firstly, we assessed the conditions required for the acquisition of sexual experience. We exposed naive females at 5 or 9 months of age to rams and subsequently assessed their response at I year of age, to the ram effect. Unexpectedly, 2 weeks pre-exposure at 5 months and under some conditions at 9 months, inhibited the ram effect at I year of age, suggesting that early contact with rams was stressful and had long-term negative effects on reproduction. Consequently, we assessed the combined effect of stress and sexual experience on responses to the ram effect. At 9 months of age, we pre-exposed naive females using sexually active rams to achieve 'positive' (voluntary contact) or 'negative' (forced contact) experiences, and assessed responses to the ram effect at a year of age. In parallel, we subjected naive females to stressful conditions at the time of the male effect. During pre-exposure, females with 'negative' contact exhibited more vigilance and stress cues and had higher levels of cortisol than 'positive' contact ewes. Regardless of pre-exposure or stress, the response to the ram effect at a year of age was inhibited. These experiments confirm that contact with sexual partners can be stressful to young ewes and highlight the need to consider their emotional state when conditioning them to the presence of rams and when managing breeding programs. (C) 2009 Elsevier Inc. All rights reserved

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

 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

La gestion de la reproduction en élevages ovins et caprins, conventionnels et biologiques : état des lieux, intérêt et acceptabilité de nouveaux outils dans six bassins de production en France

La maîtrise de la saisonnalité de la reproduction est un enjeu pour les filières ovines et caprines. Dans le contexte socio-économique actuel, l’essor de pratiques alternatives aux traitements hormonaux d’induction et de synchronisation des chaleurs et des ovulations est nécessaire en Agriculture Conventionnelle (AC) et de nouvelles perspectives d’évolution sont attendues en Agriculture Biologique (AB). À partir d’enquêtes réalisées auprès de 97 intervenants en élevage et 298 éleveurs ovins et caprins en AB et en AC, nous avons dressé un état des lieux des pratiques de gestion de la reproduction mises en œuvre dans les principaux bassins de production en France. Puis, nous avons évalué l’acceptabilité des acteurs vis-à-vis de deux outils innovants associés à la gestion de la reproduction : l’utilisation de phéromones impliquées dans l’effet mâle (comme alternative aux traitements hormonaux pour l’induction et la synchronisation des ovulations et des chaleurs) et la détection automatisée des chaleurs (pour optimiser la mise à la reproduction par IA ou pour la lutte en main). D’après les enquêtes, les pratiques de dessaisonnement de la reproduction impliquant les traitements lumineux, le recours à la mélatonine et les lactations longues sont quasi exclusivement mises en œuvre par les producteurs caprins. Les traitements hormonaux pour l’induction et la synchronisation des chaleurs et la mélatonine sont interdits par le cahier des charges en AB et donc exclusivement utilisés en AC. Au contraire, l’effet mâle est pratiqué dans l’ensemble des filières. La détection des chaleurs n’est mise en œuvre que par les éleveurs caprins et ovins laitiers. Enfin, le flushing est surtout pratiqué en filière ovine. L’utilisation potentielle des phéromones pour induire et synchroniser les chaleurs intéresse à la fois les intervenants et les éleveurs. En AB, cette technique soulève cependant des questions quant au respect du cahier des charges. L’accueil réservé aux détecteurs automatisés de chaleurs est plus mitigé. Si leur intérêt pour l’organisation du travail et la facilitation des IA a été exprimé par les éleveurs, ces derniers ont soulevé une inquiétude quant à l’inadéquation par rapport aux conduites d’élevage au pâturage a été soulevée. Si certains éleveurs sont prêts à acquérir les deux types de dispositifs, ils sont en attente des résultats concernant l’efficacité, le coût et la praticité des outils avant d’envisager de s’équiper

Sexual experience and temperament affect the response of Merino ewes to the ram effect during the anoestrous season

International audienceIn seasonally anoestrous ewes of many breeds, the introduction of rams triggers an increase in gonadotrophin secretion that induces ovulation, a phenomenon known as the 'ram effect'. The ram effect is a practical method for mating ewes outside the natural breeding season, and also can provide synchronised lambing, but the variability of the response, especially in young animals, reduces its potential for widespread application. The aim of our study was to assess two factors that are thought to contribute to the variability in young ewes: temperament and sexual experience. We used anovulatory ewes from a flock that had been genetically selected for 'calm' or 'nervous' temperament and compared the endocrine and ovarian responses to the ram effect in four groups (each n = 15): 'calm' and parous (3-6 years old); 'calm' and nulliparous (2 years old); 'nervous' and parous; and 'nervous' and nulliparous. Parous ewes, independently of their temperament, exhibited a faster endocrine response and a higher proportion of females cycling after ram introduction than nulliparous ewes. 'Nervous' ewes exhibited a higher proportion of females cycling after ram introduction than calm ewes, but only in the nulliparous group. We conclude that temperament exerts little influence on the response to the ram effect in sexually experienced ewes, and that females of 'nervous' temperament appear to respond better when sexually 'naive'. Both sexual experience and temperament need to be taken into consideration when flock management involves the ram effect. Finally, some ewes were cyclic at ram introduction, yet exhibited an increase in LH secretion even in the presence of high concentrations of progesterone. The mechanism by which the inhibitory effect of progesterone on LH secretion was bypassed needs to be clarified

Rôle of sexual experience and temperament in the response of Merinos ewes to the ram

National audienc

Nouveaux outils pour réduire le recours aux hormones pour la gestion de la reproduction en élevage ovin et caprin : avis des éleveurs et des conseillers

National audienceEn race ovine, l’Insémination Artificielle (IA) est généralement réalisée après traitement hormonal d’induction et de synchronisation des ovulations, et les brebis sont inséminées 55 h ± 1 h après le retrait de l’éponge vaginale (contenant un progestagène) en semence fraiche (Fatet et al., 2008). Une baisse de fertilité à l’IA a été observée en race Rouge de l’Ouest, ce qui a conduit les éleveurs et l’Organisme de Sélection GEODE à chercher des pistes d’amélioration. Or certains centres d’IA se sont interrogés sur l’effet du moment d’IA après retrait de l’éponge sur la fertilité : par exemple en races Lacaune viande et Blanche du Massif Central (Fréret et al., 2009) ou en race Corse (Aragni et al., 2014). Dans une étude préliminaire menée en race Rouge de l’Ouest, notre objectif a été de tester l’effet d’un allongement de 4 ou 8 h du délai d’IA moyen (par rapport au délai préconisé) sur le taux de réussite à l’IA