Abstract:La mélatonine est une substance naturellement sécrétée par la glande pinéale pendant la période obscure du nycthémère, qui transmet l’information photopériodique chez les mammifères. L’administration continue par un implant sous-cutané, comme dans les expérimentations décrites ici, permet de mimer les jours courts alors que les yeux des animaux perçoivent les jours longs naturels du printemps et de l’été. Il est nécessaire de faire subir une alternance de jours longs et de jours courts pour pouvoir maîtriser l… Show more
“… Seasonal variations in the harvest and farm price of goat milk in France (year 1992; adapted from Chemineau et al. 1996) …”
Section: Products Of Animal Origin Are Seasonally Marketedmentioning
confidence: 99%
“…This property is now commonly used in photoperiodic treatments applied on farms and/or in AI centres (see below). The definition of what is really LD and SD is not straightforward: it is possible to define a threshold of photosensitivity based on the number of light hours per day, under which LD are stimulatory and below which SD are inhibitory (see reviews Chemineau et al. 1996 and Malpaux et al.…”
Section: Neuroendocrine Mechanisms and Combination Of Endogenous Circmentioning
confidence: 99%
“…Another interesting property can be used under farm conditions to apply long days: the illumination of a specific phase of the night, the so‐called ‘photosensitive phase’, generally situated 14–16 h after dawn in sheep and 9.5 h after dusk in mares, allows animals to perceive LD even though real LD are not applied (see reviews of Malpaux et al. 1996; Chemineau et al. 1996 in sheep and goats, and Guillaume 1996 in mares).…”
Section: Neuroendocrine Mechanisms and Combination Of Endogenous Circmentioning
confidence: 99%
“… Photoperiodic treatments to control sexual activity in small ruminants raised in closed (a–c) or open (d) barns (adapted from Chemineau et al. 1996) …”
Section: Using Artificial Photoperiodic Treatments To Control Seasonamentioning
Farm mammals generally express seasonal variations in their production traits, thus inducing changing availability of fresh derived animal products (meat, milk and cheese) or performances (horses). This is due to a more or less marked seasonal birth distribution in sheep and goats, in horses but not cattle. Birth peak occurs at the end of winter-early spring, the most favourable period for the progeny to survive. Most species show seasonal variations in their ovulation frequency (presence or absence of ovulation), spermatogenic activity (from moderate decrease to complete absence of sperm production), gamete quality (variations in fertilization rates and embryo survival), and also sexual behaviour. The intimate mechanism involved is a complex combination of endogenous circannual rhythm driven and synchronized by light and melatonin. Profound and long-term neuroendocrine changes involving different neuromediator systems were described to play a role in these processes. In most species artificial photoperiodic treatments consisting of extra-light during natural short days (in sheep and goats and mares) or melatonin during long days (in sheep and goats) are extensively used to either adjust the breeding season to animal producer needs and/or to completely overcome seasonal variations of sperm production in artificial insemination centres. Pure light treatments (without melatonin), especially when applied in open barns, could be considered as non-invasive ones which fully respect animal welfare. Genetic selection could be one of the future ways to decrease seasonality in sheep and goats.
“… Seasonal variations in the harvest and farm price of goat milk in France (year 1992; adapted from Chemineau et al. 1996) …”
Section: Products Of Animal Origin Are Seasonally Marketedmentioning
confidence: 99%
“…This property is now commonly used in photoperiodic treatments applied on farms and/or in AI centres (see below). The definition of what is really LD and SD is not straightforward: it is possible to define a threshold of photosensitivity based on the number of light hours per day, under which LD are stimulatory and below which SD are inhibitory (see reviews Chemineau et al. 1996 and Malpaux et al.…”
Section: Neuroendocrine Mechanisms and Combination Of Endogenous Circmentioning
confidence: 99%
“…Another interesting property can be used under farm conditions to apply long days: the illumination of a specific phase of the night, the so‐called ‘photosensitive phase’, generally situated 14–16 h after dawn in sheep and 9.5 h after dusk in mares, allows animals to perceive LD even though real LD are not applied (see reviews of Malpaux et al. 1996; Chemineau et al. 1996 in sheep and goats, and Guillaume 1996 in mares).…”
Section: Neuroendocrine Mechanisms and Combination Of Endogenous Circmentioning
confidence: 99%
“… Photoperiodic treatments to control sexual activity in small ruminants raised in closed (a–c) or open (d) barns (adapted from Chemineau et al. 1996) …”
Section: Using Artificial Photoperiodic Treatments To Control Seasonamentioning
Farm mammals generally express seasonal variations in their production traits, thus inducing changing availability of fresh derived animal products (meat, milk and cheese) or performances (horses). This is due to a more or less marked seasonal birth distribution in sheep and goats, in horses but not cattle. Birth peak occurs at the end of winter-early spring, the most favourable period for the progeny to survive. Most species show seasonal variations in their ovulation frequency (presence or absence of ovulation), spermatogenic activity (from moderate decrease to complete absence of sperm production), gamete quality (variations in fertilization rates and embryo survival), and also sexual behaviour. The intimate mechanism involved is a complex combination of endogenous circannual rhythm driven and synchronized by light and melatonin. Profound and long-term neuroendocrine changes involving different neuromediator systems were described to play a role in these processes. In most species artificial photoperiodic treatments consisting of extra-light during natural short days (in sheep and goats and mares) or melatonin during long days (in sheep and goats) are extensively used to either adjust the breeding season to animal producer needs and/or to completely overcome seasonal variations of sperm production in artificial insemination centres. Pure light treatments (without melatonin), especially when applied in open barns, could be considered as non-invasive ones which fully respect animal welfare. Genetic selection could be one of the future ways to decrease seasonality in sheep and goats.
“…2007). The definition of what is really LD and SD is not straightforward: it is possible to define a threshold of photosensitivity based on the number of light hours per day, under which LD are stimulatory and below which SD are inhibitory (see reviews Chemineau et al. 1996 and Malpaux et al.…”
Section: Photoperiod Synchronizes An Endogenous Circannual Rhythm Of mentioning
Goats and sheep generally express seasonal variations in their sexual behaviour, spermatogenic activity (from moderate decrease to very low sperm production), gamete quality (variations in fertilization rates and embryo survival), ovulation frequency (presence or absence of ovulation), and ovulation rate (number of eggs shed per ovulation period). This induces seasonal availability of derived, fresh animal products (meat, milk and cheese) because of a more or less marked seasonal distribution of births. A complex combination of an endogenous circannual rhythm driven and synchronized by light and melatonin, which controls the pulsatile activity of GnRH neurons in the preoptic-mediobasal hypothalamus, is responsible for these changes. Dramatic and long-term neuroendocrine changes, involving different neuromediator systems and neuronal plasticity, have been shown to play a role in these processes. A strong variability between breeds exists in both species regarding the dates of onset and end of the breeding season, with a gradient of seasonality from southern to northern latitudes. Within a breed, seasonal traits are heritable; thus, genetic selection could be one way to decrease seasonality in sheep and goats in the future.
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