Seasonal changes in oestrus activity and ovulation rate in Rasa Aragonesa ewes maintained at two different body condition levels

Forcada, F.; Abecia, J.A.; Sierra, I.

doi:10.1016/0921-4488(92)90212-m

Cited by 111 publications

(64 citation statements)

References 22 publications

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“…Our results show a consistent reduction (64 vs. 113 d; P < 0.05) in the duration of seasonal anoestrus in ewes maintained from November to September at a constant, moderately high body condition score (BC) (2.9) when compared to females having a lower (but commercially viable) BC (2.3) [24] (Fig. 1).…”

Section: Nutritional Modification Of Reproductive Seasonality In Sheepsupporting

confidence: 69%

“…The greatest differences in sexual activity occurred in the transitional period between the seasonal anoestrus and the reproductive season, when a moderately high BC induced a significant increase in the proportion of ewes in oestrus. The effect of a high level of body fat reserves on sexual activity seems to be consistent among Mediterranean breeds and acts more though delaying the onset of seasonal anoestrus than by advancing the start of the new reproductive season, which is less modified by nutrition [24,27,28] and, probably, more strongly regulated by photoperiod. The inhibitory and synchronising effects of increasing daylength and long days between the spring equinox and the summer solstice on sexual activity [12] appear to be difficult to overcome using nutrition only, even in Mediterranean genotypes.…”

Section: Nutritional Modification Of Reproductive Seasonality In Sheepmentioning

confidence: 84%

“…In particular, nutrition is one of the main factors affecting ovulation rate, even over a very short time (4-6 d) [22], although this effect is not very consistent among or even within laboratories [23]. The effect of nutrition on ovulation rate is more evident over a period and when the nutritional treatments are done in the transitional period between anoestrus (seasonal or lactational) and the breeding season [24,25].…”

Section: Nutritional Modification Of Reproductive Seasonality In Sheepmentioning

confidence: 99%

“…The length of seasonal anoestrus was significantly shortened by a moderately high BC: 64 vs. 113 days; P < 0.05). Adapted from Forcada et al [24].…”

Section: Nutritional Modification Of Reproductive Seasonality In Sheepmentioning

confidence: 99%

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The effect of nutrition on the seasonality of reproduction in ewes

Forcada

Abecia

2006

Reprod. Nutr. Dev.

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-The beneficial effects of nutrition on reproduction in sheep have been described, particularly on ovulation rate. However, the relationships between nutrition and reproductive seasonality are not well known. This review will deal with the effects of body fat or food intake on sexual and hypothalamic/pituitary activity in sheep, mainly focused on Mediterranean genotypes. Although only severe malnutrition can significantly extend the length of the seasonal anestrous period, the level of fat reserves can play a significant role on reproductive seasonality delaying the onset of seasonal anoestrus, particularly on the Mediterranean environment. The effect of overfeeding on LH secretion has also been reported, specially at short term. Several experimental approaches have elucidated that both high body fat and food intake are able to modify the sensitivity of the hypothalamus to oestradiol negative feedback during seasonal anoestrus, with those effects being associated to a reduced amount of NPY mRNA and to an increase of plasma insulin, glucose and leptin concentrations, particularly in the late scenario. However, the highest receptivity to nutritional stimulation in terms of increasing LH occurs when ewes are subjected to a photoperiodic state of early anoestrus or late breeding season rather than under a photoperiod characteristic of the end of anoestrus or the beginning of the breeding season.sheep / nutrition / reproductive seasonality / gonadotropins

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Section: Nutritional Modification Of Reproductive Seasonality In Sheepsupporting

confidence: 69%

Section: Nutritional Modification Of Reproductive Seasonality In Sheepmentioning

confidence: 84%

Section: Nutritional Modification Of Reproductive Seasonality In Sheepmentioning

confidence: 99%

“…The length of seasonal anoestrus was significantly shortened by a moderately high BC: 64 vs. 113 days; P < 0.05). Adapted from Forcada et al [24].…”

Section: Nutritional Modification Of Reproductive Seasonality In Sheepmentioning

confidence: 99%

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The effect of nutrition on the seasonality of reproduction in ewes

Forcada

Abecia

2006

Reprod. Nutr. Dev.

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“…Ovulation rate It is widely known that the highest ovulation rate is achieved a few weeks after the onset of the breeding season, and lower ovulation rates have been reported in both seasonal anoestrus (for reduced seasonality breeds) and at the beginning and at the end of the breeding season (Forcada et al, 1992;Rondon et al, 1996). Therefore, most of the references in the literature deal with the effects at medium term of melatonin treatments during seasonal anoestrus.…”

Section: Effect Of Melatonin On the Ovine Ovarymentioning

confidence: 99%

Effect of exogenous melatonin on the ovary, the embryo and the establishment of pregnancy in sheep

Abecia¹,

Forcada²,

Casao³

et al. 2008

Animal

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Administration of melatonin to advance the breeding season in sheep has been widely used, since this hormone conveys the photoperiodic signal to the reproductive neuroendocrine axis. An increased lambing percentage has been reported following such treatment during anoestrus, which could be mediated through a higher rate of embryonic survival, either by an improvement in luteal function or by a reduction in the antiluteolytic mechanisms. The aim of this article is to review the body of knowledge on the effect of melatonin on the ovine ovary, the embryo and the establishment of pregnancy. Some studies using synchronized ewes have found that melatonin treatments during anoestrus do not improve ovulation rate by modifying the timing of follicle emergence, but increasing the number of ovulatory follicles by decreasing the atresia of medium and large follicles. On the other hand, the addition of melatonin to the in vitro maturation medium does not improve oocyte maturation rate in oocytes from sheep ovaries recovered either in anoestrus or in the breeding season. However, a luteotrophic effect of melatonin at either short or medium term has been reported. We have recently observed that melatonin implants tend to improve the survival of embryos collected from ewes after superovulation in anoestrus. More specifically, melatonin induced a significant reduction of the number and rate of non-viable (degenerate and retarded) embryos. Preliminary data from our laboratory suggest that the uterine sensitivity to progesterone -in terms of progesterone receptor expression -of superovulated ewes could be reduced by melatonin treatment. It can be concluded that the success of exogenous melatonin as a means to improve lamb production of sheep is due, at least in part, to an improvement of luteal support and embryonic survival.

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Climate factors affecting fertility after cervical insemination during the first months of the breeding season in Rasa Aragonesa ewes

et al. 2013

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This study was carried out to examine the impact of several climate variables on the pregnancy rate after cervical artificial insemination (AI) of Rasa Aragonesa ewes. Data were derived from 8,977 inseminations in 76 well-managed flocks performed during the first month of the breeding season (July to October). The following data were recorded for each animal: farm, year, month of AI, parity, lambing-treatment interval, inseminating ram, AI technician, and climatic variables such as mean, maximum and minimum temperature, mean and maximum relative humidity, rainfall, and mean and maximum temperature-humidity index (THI) for each day from day 12 before AI to day 14 post-AI. Means were furthermore calculated for the following periods around AI (day 0): -12 to 0, -2 to 0, AI day, 0 to 2, and 0 to 14. Logistic regression analysis indicated that the likelihood of pregnancy decreased when maximum temperature in the 2 days prior to AI was higher than 30 °C (by a factor of 0.81). Fertility was also lower for primiparous ewes and in multiparous ewes with more than five previous parturitions. Other factors with significant impact on fertility were flock, technician, inseminating ram, and a lambing-AI interval longer than 240 days. It was concluded that the 2 days prior to AI seems to be the period when heat stress had the greatest impact on pregnancy rate in Rasa Aragonesa ewes.

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Seasonal changes in oestrus activity and ovulation rate in Rasa Aragonesa ewes maintained at two different body condition levels

Cited by 111 publications

References 22 publications

The effect of nutrition on the seasonality of reproduction in ewes

The effect of nutrition on the seasonality of reproduction in ewes

Effect of exogenous melatonin on the ovary, the embryo and the establishment of pregnancy in sheep

Climate factors affecting fertility after cervical insemination during the first months of the breeding season in Rasa Aragonesa ewes

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