Abstract
To compare follicular dynamics after treatment with low doses of equine pituitary extract obtained during winter and summer and to study the relationship between follicular dynamic and environmental parameters, 21 mares were evaluated to follow follicular dynamic and ovulation, from the final of the spring transitional up to the beginning of autumnal transitional period. Mares were randomly designed to one of three treatments: Equine Pituitary Extract from summer (EPE-S), Equine Pituitary Extract from winter (EPE-W) or saline (Control). Treatments were repeated twice: March/2017, after autumnal equinox and April/2017. Temperature, humidity, solar radiation and hours/ light/day were recorded and Temperature Humidity Index (THI) was calculated. Pre-ovulatory follicles reached the greatest diameter (40.7 mm) in December (p<0.05), following the increase in light/hours/day. The smallest pre-ovulatory follicles were verified in February (34.6 mm) and March (35.0 mm) (p>0.05). After EPE, days for ovulation differed, as well as the diameter of pre-ovulatory follicles (p<0.05). EPE-W showed similar follicular dynamics as Control, ovulating smaller follicles (p<0.05) and later (p<0.05) than EPE-S. Temperature and solar radiation did not differ (p>0.05), but humidity and THI differed (p<0.05). THI was not correlated to the diameter of pre-ovulatory follicles (p=0.37), diameter of subordinate follicles (p=0.80), or number/ follicles per ovulatory wave (p=0.98). In conclusion, daylight duration influenced ovarian function; low doses of EPE-S improvede follicular growth and ovulation rate during autumnal transition period of mares; pre-ovulatory follicle diameter increased from the spring to summer, but the time required to reach ovulation decreased.
Highlights
IntroductionMares are seasonally polyestrous, showing higher reproductive activity mostly between spring and summer and the environmental effect on reproduction is due the photoperiod (Williams et al 2012)
Mares are seasonally polyestrous, showing higher reproductive activity mostly between spring and summer and the environmental effect on reproduction is due the photoperiod (Williams et al 2012). This period is characterized by two equinoxes, which occur, in the South Hemisphere, on September, 21 and March, 21, with the summer solstice (December, 21) in the meantime
For the treatment with Equine Pituitary Extract (EPE), lyophilized and purified pituitary extracts obtained in the south region of Brazil during June/July (EPE-Winter) and December (EPE-Summer) prepared as described by Guilou & Combarnous (1983) were used (Laboratório de Reprodução Animal-Unicórnio-Brasília, Brazil)
Summary
Mares are seasonally polyestrous, showing higher reproductive activity mostly between spring and summer and the environmental effect on reproduction is due the photoperiod (Williams et al 2012). This period is characterized by two equinoxes, which occur, in the South Hemisphere, on September, 21 (spring) and March, 21 (autumn), with the summer solstice (December, 21) in the meantime. All management practices involving the mares were approved by the Animal Experimentation Ethics Committee, Universidade Federal de Goiás (process # 070-17) This experiment was performed in the Brazilian tropical savannah, Goiás State, Latitude 16°40′48′′ S, Longitude 49°15′18′′ W, 750 meters above sea level, in the Southern Hemisphere, from September/2016 to April/2017. The mares were kept in pasture areas composed of Pennisetum americanum and Tifton 85, receiving mineral mixture and water ad libitum, supplemented with 1kg of commercial concentrate containing 15% protein added to 300 ml of vegetable oil, offered in individual feeders
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