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Understanding Reproductive Biology in Seasonal Breeding of Sheep

This article provides an in-depth look at the reproductive biology of sheep, focusing on the seasonal polyestrous nature of rams and ewes, which are influenced by day length and cooler temperatures. Key reproductive facts such as gestation length, the estrous cycle, and hormonal regulation are discussed, along with challenges like libido variation in rams. Effective breeding strategies, including ram-to-ewe ratios and the impact of physical fitness on mating activity, are explored to enhance flock reproductive efficiency, critical to farm profitability.

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Understanding Reproductive Biology in Seasonal Breeding of Sheep

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  1. Reproduction Sheep are seasonal polyestrous rams and ewes fall breeders day length cool temperatures ? continuous short days Impact on industry ??

  2. Reproductive facts Ewes Gestation length 143 -147 days Estrous cycle 16-17 days Estrus 12-30 hrs Ovulation near end of estrus Puberty 6-18 months

  3. Hormones Melatonin - Pineal Gland Progesterone - Corpus Luteum Estrogen - Follicles GNRH - Hypothalamus FSH & LH - Anterior Pituitary Prolactin - Anterior Pituitary Prostaglandin - Uterus

  4. Stages of Estrous Cycle Estrus Postestrus Diestrus Proestrus Estrus ect.

  5. Rams Testosterone - Leydig Cells Temperature Regulation 5-7° below body T of 102° > 99° Problems Cremaster Tunica Dartos Pampiniform Plexus

  6. Rams Epididymis - four functions Transport Concentration Maturation Storage

  7. Breeding Capacity Spermatogenesis - 42 days 1 billion sperm per cc Each Ejaculate - .5 - 1.5 cc 5.5 billion sperm produced per day

  8. Tremendous Variation in Libido Duds and Studs, US Sheep Station 38% Rated as Low Performers @ 10% Showed no interest in Ewes 28% of unexposed ram lambs are inactive Environmental Temperatures above 770

  9. Ram : Ewe ratios Varies from 1-25 to 1-200 First service conception High Medium 1:50 77 58 1:200 50 33 More estrus ewes = more services 6-20/day

  10. Ram staying power 20 ejaculates per day for 20 days did not deplete semen concentration below acceptable levels

  11. Multiple Sire Mating Groups Dominant ram - Harem Subordinates - In and Outers Why Increase Mating Activity Goal: minimum of 3 services/ewe

  12. Physically Fit Rams exercised 1.8 miles per day for 40 days pre-breeding Increased lambs born by 10%

  13. Sheep Flock Math % ewes lambing of ewes exposed Lambs born per ewe lambing Lambs born per ewe exposed Lamb survival birth to weaning Pounds weaned/ee

  14. Reproductive efficiency Critical to flock profit Genetics or management???

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