Animal Reproduction/Theriogenology https://www.youtube.com/channel/UCHzZhYqMy10vsVRZdddEkUg

1. THER 608
Physiology of Reproduction
Prof. Dr. Nasim Ahmad
Breeding Season in Farm Animals
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2. Day Length, Melatonin and GnRH
• Relation of daylight length with melatonin
(M) production is inverse
• DLL α 1 (For both long day and short day breeders)
M
• OR
• ↑ DLL → ↓ M (For both long day and short day
breeders)
• ↓ DLL → ↑ M (For both long day and short day
breeders)
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3. Relation of melatonin (M) with production of GnRH
• M α GnRH (For short day breeders)
• M α 1 (For long day breeders)
• GnRH
OR
• ↑ M → ↑ GnRH (For short day breeders)
• ↓ M → ↓ GnRH (For short day breeders)
• ↑ M → ↓ GnRH (For long day breeders)
• ↓ M → ↑ GnRH (For long day breeders)
Explanation:
• 1. For shortday breeders, (M) melatonin production is
directly proportional to GnRH production
• 2. For longday breeders, (M) melatonin production is
inversely proportional to GnRH production.
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4. 4

5. BREEDING SEASON
• Photoperiods (day length) and environmental temperature
and humidity affect the annual sexual cycles. Some species
show pronounced seasonal pattern eg., Sheep, Horse
whereas others do not eg., cattle, buffalo.
• Breeding season is generally longer in males than in the
females of the affected species, moreover, males are not that
much affected compared with females as semen production
continue.
• Short day breeders: (sexual activity during winter; Sheep,
goat,) Some Sheep breeds (eg., Merino have long season,
other eg., Blackface have short season.
• Long day breeders: (sexual activity during summer; Mare)
• Silent ovulatory cycles or ‘short cycles’ at the beginning and
end of the sexual session.
• Though rams can mate through out the year, testis weight,
testosterone, and Gn’s are minimal from January to May.
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6. BREEDING SEASON
• Factors regulating breeding season include, environmental,
physiologic, and social. They in turn mediate the endocrine
and neuroendocrine mechanisms
• Photoperiodicity results in seasonality in two mechanisms
– Direct action on the hypothalamic pituitary axis
– Change in the sensitivity of CNS to negative feedback from
steroid
• Mares show ovarian silence and stallions show low plasma
testosterone and LH levels from October to February.
Reproductive cyclicity occur from May to October. Best
conceptions occur from May to July
• Minimum fertility becomes evident in cattle in June and
maximum in November
• Maximum sperm abnormalities were recorded during summer
months in Crossbred bulls (Friesian x Sahiwal) in Pakistan
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7. SEASONAL REPRODUCTION IN EWE
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8. PERIODS OF SEXUAL ACTIVITY IN EWES
Sexual activity is dependent on photoperiod but not the calendar months
One year photo period cycle
Six months photo period
cycle
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9. SEASONAL VARIATION IN FERTILITY
(NON RETURN RATE, 60-90 DAYS) IN CATTLE
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10. Effect of Season on Pattern of
Calving in Buffaloes
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11. Seasonal occurrence of ovulations
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12. AN INTEGRATIVE CONCEPTUALIZATION OF THE ENVIRONMENTAL
CONTROL OF REPRODUCTION IN A MAMMAL
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