The breeding season of the sheep with particular reference to its modification by artificial means using light

Yeates, N. T. M.

doi:10.1017/s0021859600004299

Cited by 298 publications

(124 citation statements)

References 65 publications

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“…The reversal of the annual photoperiodic cycle causes the reproductive season to shift by six months [5]. In addition, within six months, ewes exposed to light regimes that provided a natural annual variation in daylength, have two breeding seasons per year [6].…”

Section: Role Of Photoperiod In Reproductive Seasonalitymentioning

confidence: 99%

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: Role Of Photoperiod In Reproductive Seasonalitymentioning

confidence: 99%

The effect of nutrition on the seasonality of reproduction in ewes

Forcada

Abecia

2006

Reprod. Nutr. Dev.

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“…Firstly, the annual period of reproduction begins in late summer as the daylength is becoming shorter and terminates in late winter as daylength is gradually lengthening (Yeates, 1949 ;Hafez, 1952). Secondly, under artificial photoperiodic conditions, short days can induce a period of reproduction while long days inhibit the process (Maul6on and Rougeot, 1962 ;Legan and Karsch, 1980 ; Lincoln and Short, 1980 (Robinson and Karsch, 1984).…”

Section: Introductionmentioning

confidence: 99%

Timing the breeding season of the ewe : what is the role of daylength ?

Robinson¹,

Karsch²

1988

Reprod. Nutr. Dévelop.

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“…It is well established that seasonal testicular function in rams and ovarian activity in ewes are regulated by photoperiod and that steroid feedback is involved in this mechanism (for reviews see : Yeates 1949;Ortavant et al 1964;Lincoln and Short 1980). The gonadectomized ram and ewe model has thus proved an invaluable means of elucidating many of the physiological aspects of the seasonal sexual response of the entire animal (Robinson 1982).…”

Section: Introductionmentioning

confidence: 99%

Response of Pre-pubertally Castrated Rams and Ewes to Artificial PhotoperiodChanges in Plasma LH and Prolactin

Poulton¹

1986

Aust. Jnl. Of Bio. Sci.

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Castrate rams and ovariectomized ewes were maintained in the presence of entire rams and ewes and subjected to successive periods of alternating 6 h light: 18 h darkness ('short' days) and 18 h light: 6 h darkness ('long' days) preceeded by a period of 12 h light: 12 h darkness ('constant' light days). Plasma concentrations of LH and prolactin were measured in the castrate animals in order to determine how LH and prolactin secretion responded to (i) the artificial light regime and (ii) corresponding periods of elevated or depressed testicular and ovarian activity in the entire rams and ewes.There was no variation in mean plasma LH concentrations or LH pulse frequency with either the changes in photoperiod or the phases of gonadal activity in the entire animals. However, there was a highly significant (P < 0'001) relationship between prolactin secretion and the artificial photoperiod in both castrate groups with high and low levels coinciding with long and short days respectively.In addition, there was a marginally significant (P < 0'1) relationship between prolactin secretion in the castrate ram and the stage of testicular activity in the entire rams with elevated levels associated with regressed activity. Prolactin secretion in the ovariectomized ewes was significantly (P < O' 05) related to the phase of ovarian development with high levels associated with acyclic activity.It is concluded that LH secretion and pituitary responsiveness to exogenous GnRH were not modified by the artificial light regime. However, the changing light pattern was physiologically 'perceived' by the castrate animals as indicated by a concomitant variation in plasma prolactin concentrations.

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The breeding season of the sheep with particular reference to its modification by artificial means using light

Abstract: At the beginning of the present century Heape (1900), describing the sexual season of mammals, pointed out that sheep in the British Isles are sexually active during only a portion of the year.

Cited by 298 publications

References 65 publications

The effect of nutrition on the seasonality of reproduction in ewes

The effect of nutrition on the seasonality of reproduction in ewes

Timing the breeding season of the ewe : what is the role of daylength ?

Response of Pre-pubertally Castrated Rams and Ewes to Artificial PhotoperiodChanges in Plasma LH and Prolactin

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