The timing of reproductive activity in seasonal breeding sheep relies on daily photoperiodic signals being relayed to provide information on the time of year
نویسندگان
چکیده
structural and immunocytochemical changes taking place during the day and at night in developing sheep pineal gland under natural non-stimulatory photoperiods (summer solstice). Additionally, the diurnal cycle of plasma melatonin levels was charted and differences between diurnal and nocturnal pineal melatonin concentrations were analyzed. 36 ewes of three different ages were examined: infants (1-6 months old), pubertal and early fertile age (9-24 months old) and adults (36-60 months old). Plasma and pineal gland melatonin levels were higher in pubertal sheep than in infants or adults. Pubertal sheep pineal glands were also heavier, contained a larger number of pinealocytes and interstitial cells and displayed more evident innervation and vascularisation than infants or adults. There was no difference in the number of pinealocytes and interstitial cells between animals killed during daylight or at night. Gland weight, pinealocyte nuclear profile areas and plasma melatonin concentrations were all significantly higher at night than during the day.
منابع مشابه
The role of nutrition and photoperiod in the timing of puberty.
In animals that are kept in temperate latitudes and that are seasonal in their breeding activity, nutritional and photoperiodic signals operate in harmony to time the activation of the gonadotrophin-releasing hormone (GnRH) pulse generator in the brain and trigger puberty. These signals ensure that within the constraints imposed by the circannual changes in the environment, body size and time o...
متن کاملSelenium and iodine status of sheep in the Markazi province, Iran
The aim of this study was to provide preliminary quantitative information on selenium and iodine statusof sheep in Markazi province, Iran. Selenium and iodine status of grazing sheep were measured for 57different flocks in 14 regions over one year. The districts were selected to represent major sheep growingareas in the province. Blood samples were collected from 2 to 3-year-old ewes during sum...
متن کاملSeasonality of reproduction in sheep
Unlike most domestic livestock species, sheep are widely known as an animal with marked seasonality of breeding activity. The annual cycle of daily photoperiod has been identified as the determinant factor of this phenomenon, while environmental temperature, nutritional status, social interactions, lambing date and lactation period are considered to modulate it. The aim of this paper is to revi...
متن کاملThe effect of nutrition on the seasonality of reproduction in ewes.
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 mal...
متن کاملAncestral TSH Mechanism Signals Summer in a Photoperiodic Mammal
In mammals, day-length-sensitive (photoperiodic) seasonal breeding cycles depend on the pineal hormone melatonin, which modulates secretion of reproductive hormones by the anterior pituitary gland [1]. It is thought that melatonin acts in the hypothalamus to control reproduction through the release of neurosecretory signals into the pituitary portal blood supply, where they act on pituitary end...
متن کامل