Ovarian responses of anestrous ewes to the "ram effect"

Ungerfeld, Rodolfo; Pinczak, A.; Forsberg, M.; Rubianes, E.

doi:10.4141/a02-005

Cited by 28 publications

(12 citation statements)

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“…The depth of anoestrus is a factor often cited in the literature as influencing the response to the 'ram effect' (Rosa and Bryant, 2002;Ungerfeld et al, 2004). We tested the effectiveness of the 'ram effect' during early, middle and late anoestrus.…”

Section: Discussionmentioning

confidence: 99%

“…Abnormal cycles included short cycles and delayed cycles. Short cycles were defined as cycles in which the concentration of progesterone was above 0.5 ng/ml for 1 to 2 days indicating that ovulation occurred, but the luteal phase was shortened to less than 3 days (Chemineau et al, 2006) and delayed cycles were defined as cycles in which the concentration of progesterone first rose above 0.5 ng/ml after day 7, indicating that the luteal phase was delayed (Ungerfeld et al, 2002). Examples of ovarian responses are shown in Figure 2.…”

Section: Hormone Assaysmentioning

confidence: 99%

“…Although the origins of variability in the response to the 'ram effect' have been investigated (Rosa and Bryant, 2002;Ungerfeld et al, 2004), the causes and mechanisms are not well defined. The depth of anoestrus defined as the proportion of ewes in a flock showing spontaneous ovulation, is one factor that may contribute to this variability (Thimonier et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

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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’

Chanvallon

Sagot

Pottier

et al. 2011

Animal

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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 (Mé rinos d'Arles and Romane), one highly seasonal (Mouton Vendé en) and one intermediate (Iˆle-de-France) breeds. Anoestrus was longer and deeper in Mouton Vendé en and Iˆle-deFrance than in Romane or Mé rinos 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 Mé rinos 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.

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Section: Discussionmentioning

confidence: 99%

Section: Hormone Assaysmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Chanvallon

Sagot

Pottier

et al. 2011

Animal

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“…Olfactory signals, or pheromones, are perhaps the most important, and they can inhibit (e.g., block pregnancy [1]) or facilitate (e.g., synchronization of estrus [2][3][4]) the reproductive process. Arguably, the most profound facilitatory effect of male sociosexual stimuli identified to date is observed in ungulates such as sheep, in which exposure to males leads within minutes to a complete change in the female's reproductive status from quiescent to fertile [5][6][7]. Moreover, the epidermal pheromone of sheep and goats seems to encode specific information about male identity, as only unfamiliar (''novel'') males seem able to induce ovulation [8,9].…”

Section: Introductionmentioning

confidence: 99%

Rapid Induction of Cell Proliferation in the Adult Female Ungulate Brain (Ovis aries) Associated with Activation of the Reproductive Axis by Exposure to Unfamiliar Males1

Hawken

Jorre

Rodger

et al. 2009

Biology of Reproduction

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In many species, the reproductive centers of the brain are profoundly affected by sociosexual stimuli. This is particularly evident in female ungulates such as sheep, in which exposure to males switches them from reproductively quiescent to fertile. In two experiments with female sheep, we tested whether the brain centers that control gonadotropin-releasing hormone (GnRH) neuronal activity respond differentially to ''novel'' vs. familiar males and whether the neuroendocrine response is associated with increased cell proliferation in the hippocampus, a site associated with memory formation. In experiment 1, groups of 10 female sheep that had previously been habituated to males for 3 mo were re-exposed to familiar males or were exposed to novel males. Only the novel males increased luteinizing hormone (LH) pulse frequency, indicating stimulation of GnRH neuronal activity. In experiment 2, groups of six female sheep were injected with bromodeoxyuridine (BrdU) and then maintained in isolation from males or exposed to novel males. Two days later, the hippocampus and hypothalamus were removed and processed for fluorescence immunohistochemistry. Again, exposure to males increased LH pulse frequency. Most important, male exposure also doubled the number of BrdUpositive cells in the dentate gyrus of the hippocampus. No BrdUpositive cells were detected in the hypothalamus. We conclude that the stimulus from novel males switches on the reproductive centers of the brain of female sheep and rapidly doubles the rate of cell proliferation in the hippocampus. The rapidity of this response contrasts with rodents, in which several days of exposure to male pheromones seem necessary for an effect on neurogenesis.

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“…3,6 However, recent work has demonstrated that physical (and consequently olfactory, auditive and hearing) isolation between genders is dispensable for male effect usage based ovulation induction in sheep and goats. 3,7 However, these studies dissected the physiological response and ovulation parameters of omitting ram physical isolation for male effect, 3,7,8 but further reproductive parameters such as pregnancy and prolificacy rates remained to be described.…”

Section: Introductionmentioning

confidence: 99%

The influence of separation distance during the preconditioning period of the male effect approach on reproductive performance in sheep

et al. 2014

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The study was aimed to test the effect of the separation distance between males and females during the preconditioning period on the reproductive performance of Santa Inês ewes after the male effect. Santa Inês ewes were kept at distances of 3000 m (T1), 3 m (T2), and 300 m (T3) from rams for 60 days before starting 45-day mating seasons during the dry period (DP) and rainy periods (RP). Mating events were observed daily at 6:00 h and 16:00 h by trained personnel for one hour intervals. Estrous were scored as synchronized when observed until day 5 after breeding season start. Pregnancy diagnosis was performed by ultrasonography. In the DP, the first estrous averaged at 15.45±10.36 (T1), 9.25±6.41 (T2) and 13.05±10.24 (T3) days and in RP was 8.73±5.84 (T1), 9.30±5.62 (T2) and 6.10±5.66 (T3) days. All females cycled during both DP and RP. Estrous synchronization occurred in 20% of the females during DP (T1: 30%, T2: 15%, and T3: 15%). In the RP, estrous synchronization occurred in 40% of all females (T1: 30%, T2: 35%, and T3: 45%). The pregnancy rates in DP and RP were T1: 85%, T2: 80%, and T3: 75%. The results show that the male effect can be obtained simply by avoiding physical contact between males and females throughout the year under tropical conditions.

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Ovarian responses of anestrous ewes to the "ram effect"

Cited by 28 publications

References 9 publications

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

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

Rapid Induction of Cell Proliferation in the Adult Female Ungulate Brain (Ovis aries) Associated with Activation of the Reproductive Axis by Exposure to Unfamiliar Males1

The influence of separation distance during the preconditioning period of the male effect approach on reproductive performance in sheep

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