How does Heat Stress affect Reproduction?

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How does Heat Stress affect Reproduction?

• Reduced Estrus Expression
• Follicular development
• Growth patterns
• Dominance
• Steroidogenesis
• CL development and function
• Embryonic development
• Fetal-Calf-Milk Yield after delivery

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Ovarian follicles 1. Follicular growth
2. Estradiol production
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THE ESTROUS CYCLE
Dominance
Hormone concentration
Atresia
Deviation
Recruitment
Estrus
Estrus
5
10
15
4
Heat Stress Attenuates Follicular Dominance in
Dairy Cows
5
Inhibin in Plasma
0.4
Ir-Inhibin (ng/ml)
0.3
0.2
4
9
14
19
Day of cycle
Wolfenson et al., 2000.
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Early Emergence of The Preovulatory Follicles
Heat stressed
Cooled
Follicular diameter (mm)
Day of Cycle
Wolfenson et al., 2000.
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Stress Increased Number of Large Follicles
2
Heat stress
Cooled
Large follicles ()
1
0
13
14
15
16
17
18
19
20
Day of cycle
Wolfenson et al., 2000.
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Twin Pregnancy D28
Twin Births Increase in the Summer Months
Embryos in left and right horn, CL in left ovary
and CL and big follicle in right ovary. We are
seen a lot of this big follicles during hot
weather Bartolome J. and Thatcher, W.W.
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Timed Insemination to Eliminate the need for Heat
Detection Combined with Environmental Cooling
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Effect of Timed AI on Fertility in Summer
Pregnancy rate
Days to First AI
50
100
Days open
80
40
60
Days
Pregnancy rate ()
30
40
20
20
10
0
Timed AI
Control
(de la Sota et al., 1997 Florida)