The physiological responses of anovulatory ewes to the introduction of rams — A review

Martin, Graeme; Oldham, C.M.; Cognie, Y.; Pearce, Darryl T

doi:10.1016/0301-6226(86)90031-x

Cited by 277 publications

(192 citation statements)

References 52 publications

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“…The early occurrence of estrus could be explained by ewes with cycling activity before male introduction. In cyclic ewes, exposition to a ram can advance the LH surge [13], shorten the follicular phase [14], and even cause early luteolysis, but no ovulation can be induced [15]. However, the high estrous activity around Day 10 after joining indicates that ovulation did occur in most ewes immediately after exposure to the rams and that the following luteal phase was shortened.…”

Section: Discussionmentioning

confidence: 99%

Reproductive performance of Lacaune dairy sheep exposed to artificial long days followed by natural photoperiod without and with additional progestagen treatment during the nonbreeding season

et al. 2015

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This study compared the reproductive performance of Lacaune dairy ewes exposed to a light program and subsequent male introduction without (n = 36) or with (n = 36) an additional 6-day progestagen treatment during the nonbreeding season. All ewes were exposed to extended day length (16 hours light and 8 hours darkness) for 77 days during winter (December 15 until March 2) followed by increasing natural photoperiod. At the end of the photoperiodic treatment, three blood samples were collected 6 days apart for progesterone (P4) analysis to determine cyclic activity. One half of the ewes were additionally subjected to a 6-day progestagen treatment in combination with PGF2 and eCG at insert withdrawal. Rams fitted with marking harnesses were introduced to females for 45 days and marked ewes recorded. Ewes exposed to the light program only were joined 40 days after the end of photoperiodic treatment, and ewes with additional progestagen treatment were joined 1 day after insert removal (40-44 days after the end of photostimulation). Lambing data were recorded and fertility (percentage of ewes lambing, lambing rate, and litter size) assessed to the first service period and overall. Mean serum P4 concentrations were similarly (P > 0.05) low in both groups (0.4-0.7 ng/mL vs. 0.4-0.6 ng/mL). On the basis of elevated P4 levels (>1 ng/mL), evidence of luteal activity was found in 27.8% of the ewes at the end of the light program. Estrus response was equally high (97.2%) and estrus distribution highly synchronized in progestagen-treated ewes (91.7% within 4 days). In ewes exposed to the light program only, estrous activity was recorded within 4 days (six ewes), from Day 8 to Day 17 (17 ewes) and from Day 19 to Day 25 (12 ewes) after joining. The percentage of ewes that lambed to the first service period was higher (P < 0.05) in ewes exposed to the light program only than that in the group additionally treated with progestagen/PGF2 /eCG (94.4% vs. 69.4%). Overall, the percentage of lambing ewes was similar in both groups (97.2% and 94.4%), and lambing rates (1.4-1.9) and litter sizes (1.9-2.1) were high and not influenced (P > 0.05) by the treatment. In conclusion, this study reports that exposition of Lacaune ewes to artificial long days followed by natural day length and male introduction is highly effective to induce fertile estrous activity during the nonbreeding season and offers a reliable and practical alternative to hormonal manipulation for out-of-season breeding in sheep. a b s t r a c tThis study compared the reproductive performance of Lacaune dairy ewes exposed to a light program and subsequent male introduction without (n ¼ 36) or with (n ¼ 36) an additional 6-day progestagen treatment during the nonbreeding season. All ewes were exposed to extended day length (16 hours light and 8 hours darkness) for 77 days during winter (December 15 until March 2) followed by increasing natural photoperiod. At the end of the photoperiodic treatment, three blood samples were collected 6 days apart for progesterone (...

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Section: Discussionmentioning

confidence: 99%

Reproductive performance of Lacaune dairy sheep exposed to artificial long days followed by natural photoperiod without and with additional progestagen treatment during the nonbreeding season

et al. 2015

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“…20 mg per ewe) at exactly the same time as the introduction of males. This provokes an important delay in the post-introduction events: LH surge and subsequent ovulations are delayed from 24 to 72 h, depending on the experiments [5,17,56,57]. This was also demonstrated in goats [58,59].…”

Section: How Exogenous P4 Acts To Completely Suppress Short Cycles? Imentioning

confidence: 91%

“…This hypothesis is reinforced by the fact that an early induction of premature ovulations using GnRH injections in P4 treated ewes, restores short-lifespan CL [11,17]. The hypothesis of a longer duration of the follicular phase in females experiencing a normal lifespan CL duration has also been proposed based on a difference in the timing of the LH surge after introduction of rams in a limited number of ewes [5,17]. But very few experiments or observations have been done.…”

Section: How Exogenous P4 Acts To Completely Suppress Short Cycles? Imentioning

confidence: 99%

“…Many authors have decorticated the short, medium and long-term response to the male effect conducing to a rationalisation in the understanding of female responses (see reviews in sheep [4][5][6][7], in goats [8][9][10]). However, to our knowledge, in spite of these important advances, the general mechanism to explain the existence of an abnormal (i.e.…”

Section: Introductionmentioning

confidence: 99%

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Male-induced short oestrous and ovarian cycles in sheep and goats: a working hypothesis

et al. 2006

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-The existence of short ovulatory cycles (5-day duration) after the first male-induced ovulations in anovulatory ewes and goats, associated or not with the appearance of oestrous behaviour, is the origin of the two-peak abnormal distribution of parturitions after the "male effect". We propose here a working hypothesis to explain the presence of these short cycles. The male-effect is efficient during anoestrus, when follicles contain granulosa cells of lower quality than during the breeding season. They generate corpora lutea (CL) with a lower proportion of large luteal cells compared to small cells, which secrete less progesterone, compared to what is observed in the breeding season cycle. This is probably not sufficient to block prostaglandin synthesis in the endometrial cells of the uterus at the time when the responsiveness to prostaglandins of the new-formed CL is initiated and, in parallel, to centrally reduce LH pulsatility. This LH pulsatility stimulates a new wave of follicles secreting oestradiol which, in turn, stimulates prostaglandin synthesis and provokes luteolysis and new ovulation(s). The occurrence of a new follicular wave on days 3-4 of the first male-induced cycle and the initiation of the responsiveness to prostaglandins of the CL from day 3 of the oestrous cycle are probably the key elements which ensure such regularity in the duration of the short cycles. Exogenous progesterone injection suppresses short cycles, probably not by delaying ovulation time, but rather by blocking prostaglandin synthesis, thus impairing luteolysis. The existence, or not, of oestrous behaviour associated to these ovulatory events mainly varies with species: ewes, compared to does, require a more intense endogenous progesterone priming; only ovulations preceded by normal cycles are associated with oestrous behaviour. Thus, the precise and delicate mechanism underlying the existence of short ovulatory and oestrous cycles induced by the male effect appears to be dependent on the various levels of the hypothalamo-pituitary-ovario-uterine axis.male-effect / ovulation / corpus luteum / cycle / oestrus / uterus

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“…This characteristic imposes strong constraints on husbandry, in terms of work organization and seasonal availability of animal products (Chemineau et al, 2008). Researches in animal agriculture over the last 50 years have focused on understanding the physiological and environmental mechanisms driving this cycle, and trying to find ways to control it using hormonal treatments, exposure to artificial light regimens or through the manipulation of socio-sexual signals -the male effect (Thimonier, 1981;Martin et al, 1986).…”

Section: Introductionmentioning

confidence: 99%

Animal Board Invited Review: Sheep birth distribution in past herds: a review for prehistoric Europe (6th to 3rd millennia BC)

Balasse

Tresset

Bălășescu³

et al. 2017

Animal

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In temperate latitudes sheep have a seasonal reproductive behaviour, which imposes strong constraints on husbandry in terms of work organization and availability of animal products. During the last 50 years, researchers have focused on understanding the mechanisms driving small ruminants' reproduction cycles and finding ways to control them. This characteristic is inherited from their wild ancestor. However, the history of its evolution over the 10 millennia that separates present day European sheep from their Near Eastern ancestors' remains to be written. This perspective echoes archaeologists' current attempts at reconstructing ancient pastoral societies' socio-economical organization. Information related to birth seasonality may be retrieved directly from archaeological sheep teeth. The methodology consists of reconstructing the seasonal cycle record in sheep molars, through sequential analysis of the stable oxygen isotope composition (δ 18 O) of enamel. Because the timing of tooth development is fixed within a species, inter-individual variability in this parameter reflects birth seasonality. A review of the data obtained from 10 European archaeological sites dated from the 6th to the 3rd millennia BC is provided. The results demonstrate a restricted breeding season for sheep: births occurred over a period of 3 to 4 months, from late winter to early summer at latitudes 43°N to 48°N, while a later onset was observed at a higher latitude (59°N). All conclusions concurred with currently held expectations based on present day sheep physiology, which, aside from the historical significance, contributes to the reinforcing of the methodological basis of the approach. Further study in this area will permit regional variability attributable to technical choices, within global schemes, to be fully reported.

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The physiological responses of anovulatory ewes to the introduction of rams — A review

Cited by 277 publications

References 52 publications

Reproductive performance of Lacaune dairy sheep exposed to artificial long days followed by natural photoperiod without and with additional progestagen treatment during the nonbreeding season

Reproductive performance of Lacaune dairy sheep exposed to artificial long days followed by natural photoperiod without and with additional progestagen treatment during the nonbreeding season

Male-induced short oestrous and ovarian cycles in sheep and goats: a working hypothesis

Animal Board Invited Review: Sheep birth distribution in past herds: a review for prehistoric Europe (6th to 3rd millennia BC)

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