The Effect of Short-Term Nutritional Supplementation and Body Condition on the Pituitary and Ovarian Responses of Anoestrous Ewes to the “Ram Effect”

Johnson, Linda Marlene; Nys, Charlotte; Chanvallon, Audrey; François, Dominique; Fassier, Thierry; Menassol, Jean-Baptiste; Brown, Hannah; Lardic, Lionel; Scaramuzzi, Rex

doi:10.4172/2157-7579.s2-001

Cited by 4 publications

(2 citation statements)

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“…Consequently, until recently there has been little detailed analysis of the concentrations of circulating E 2 in the anoestrous ewes ovulating in response to the introduction of rams. One report from our group (Johnson et al 2011) showed that the plasma concentrations of E 2 increased 8 h after the introduction of rams and that the occurrence of the LH surge in response to socio-sexual stimulation was strongly related to the concentration of E 2 during the 48 h following the introduction of ram. In addition, there have been a number of reports in the males of several species, where exposure to females increased LH secretion and that this was followed by increased testosterone secretion (Katongole et al 1971, Rose et al 1972, Kamel et al 1975, Gonzalez et al 1988.…”

Section: Discussionmentioning

confidence: 99%

“…In fact, one study from 1978 concluded that there was no change in the concentrations of plasma E 2 in ewes stimulated by the 'ram effect' . Recent results from our laboratory have indicated that there was a close relationship between the induction of a LH surge after introduction of rams and increased systemic concentrations of E 2 at the time of the LH surge (Johnson et al 2011).…”

Section: Introductionmentioning

confidence: 99%

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Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the ram effect

Fabre-Nys¹,

Chanvallon²,

Debus³

et al. 2015

Reproduction

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The proportion of anoestrous ewes ovulating after exposure to a sexually active ram is variable mainly due to whether an LH surge is induced. The aim of this study was to determine the role of oestradiol (E 2 ) in the ram-induced LH surge. In one study, we measured the plasma concentrations of E 2 in ewes of different breeds before and after the 'ram effect' and related these patterns to the presence and latency of the LH surge, while another compared ovarian responses with the 'ram effect' following exposure to rams for 2 or 12 h. In all ewes, the concentration of E 2 increased 2-4 h after rams were introduced and remained elevated for 14.5G0.86 h. The quantity of E 2 secreted before the LH surge varied among breeds as did the mean concentration of E 2 . The granulosa cells of IF ewes collected after 12 h exposure to rams secreted more E2 and progesterone and had higher levels of StAR than the 2 h group but in MV ewes there was no differences between these groups for any of these parameters. These results demonstrate that the LH surge induced by the rams is a result of increased E 2 secretion associated with increased levels of STAR in granulosa cells and that these responses varied among breeds. The results suggest that the variable occurrence of a LH surge and ovulation may be the result of variable ovarian responses to the 'ram effect' and insensitivity of the hypothalamus to the E 2 -positive feedback signal. Free French abstract: A French translation of this abstract is freely available at

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the ram effect

Fabre-Nys¹,

Chanvallon²,

Debus³

et al. 2015

Reproduction

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The â€œram effectâ€: new insights into neural modulation of the gonadotropic axis by male odors and socio-sexual interactions

2015

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Reproduction in mammals is controlled by the hypothalamo-pituitary-gonadal (HPG) axis under the influence of external and internal factors such as photoperiod, stress, nutrition, and social interactions. Sheep are seasonal breeders and stop mating when day length is increasing (anestrus). However, interactions with a sexually active ram during this period can override the steroid negative feedback responsible for the anoestrus state, stimulate luteinizing hormone (LH) secretion and eventually reinstate cyclicity. This is known as the “ram effect” and research into the mechanisms underlying it is shedding new light on HPG axis regulation. The first step in the ram effect is increased LH pulsatile secretion in anestrus ewes exposed to a sexually active male or only to its fleece, the latter finding indicating a “pheromone-like” effect. Estradiol secretion increases in all ewes and this eventually induces a LH surge and ovulation, just as during the breeding season. An exception is a minority of ewes that exhibit a precocious LH surge (within 4 h) with no prior increase in estradiol. The main olfactory system and the cortical nucleus of the amygdala are critical brain structures in mediating the ram effect since it is blocked by their inactivation. Sexual experience is also important since activation (increased c-fos expression) in these and other regions is greatly reduced in sexually naïve ewes. In adult ewes kisspeptin neurons in both arcuate and preoptic regions and some preoptic GnRH neurons are activated 2 h after exposure to a ram. Exposure to rams also activates noradrenergic neurons in the locus coeruleus and A1 nucleus and increased noradrenalin release occurs in the posterior preoptic area. Pharmacological modulation of this system modifies LH secretion in response to the male or his odor. Together these results show that the ram effect can be a fruitful model to promote both a better understanding of the neural and hormonal regulation of the HPG axis in general and also the specific mechanisms by which male cues can overcome negative steroid feedback and trigger LH release and ovulatory cycles.

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Interactions between Nutrition and the “Ram Effect” in the Control of Ovarian Function in the Merino Ewe

Khaiseb

Hawken

Martin

2022

Animals

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We tested whether short-term nutritional supplementation (500 g lupin grain per head daily) would affect the response of ewes to the ram effect. Experiment 1 (end of non-breeding season): ewes were supplemented for either Days −6 to −1 relative to ram introduction (n = 24) or for 12 days after ram introduction (Days 11 to 22 of the ram-induced cycle; n = 29). Controls (n = 30) were not supplemented. Across all groups, 94–100% of ewes ovulated. Supplementation before ram introduction did not affect ovulation rate at the ram-induced ovulation but increased it during the ram-induced cycle (Control 1.37; supplemented 1.66; p < 0.05). Experiment 2 (the middle of non-breeding season): the supplement was fed for Days −5 to −1 relative to ram introduction. Again, supplementation did not increase number ovulating (Control 16/29; Supplemented 10/29) but it did increase ovulation rate at the ram-induced ovulation (Control 1.31; Supplemented 1.68; p < 0.05). In neither experiment did supplementation affect the frequency of short cycles. Supplementation before ram introduction did not improve the percentage of ewes ovulating or reduce the frequency of short cycles (so will not improve the synchrony of lambing). However, supplementation after ram introduction can increase prolificacy.

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The Effect of Short-Term Nutritional Supplementation and Body Condition on the Pituitary and Ovarian Responses of Anoestrous Ewes to the “Ram Effect”

Cited by 4 publications

References 30 publications

Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the ram effect

Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the ram effect

The â€œram effectâ€: new insights into neural modulation of the gonadotropic axis by male odors and socio-sexual interactions

Interactions between Nutrition and the “Ram Effect” in the Control of Ovarian Function in the Merino Ewe

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The Effect of Short-Term Nutritional Supplementation and Body Condition on the Pituitary and Ovarian Responses of Anoestrous Ewes to the “Ram Effect”

Cited by 4 publications

References 30 publications

Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the ram effect

Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the ram effect

The â€œram effectâ€: new insights into neural modulation of the gonadotropic axis by male odors and socio-sexual interactions

Interactions between Nutrition and the “Ram Effect” in the Control of Ovarian Function in the Merino Ewe

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The â€œram effectâ€: new insights into neural modulation of the gonadotropic axis by male odors and socio-sexual interactions