3. Seasonality of Reproduction and Testicular Thermoregulation

Examples of seasonal breeders?

-horse

-sheep

What is the purpose of the ovulatory cycle?

attract a male

What are the 3 female reproductive patterns?

Polyestrus

Seasonally polyestrus

Seasonally monoestrus

Polyestrus (and examples)

Continuously cycling, not affected by season

-sow, queen, cow, rodents, camelids, birds

Seasonally polyestrus (and examples)

Many heats within a season

-ewe, mare, nanny, doe, elk

Seasonally monestrus (and examples)

Only one chance during the season to show heat and hopefully breed

-dog, wolf, fox, bear

What are short day breeders?

-those species that breed during short days/long nights

What's different between short day adults and younger females

-about 10% more adults are cycling during long days than younger females

-the length of the breeding season is slightly longer for adults (because adults have had more exposure to hormones over their lifetime)

How do seasons affect rams?

-seasonal effect on scrotal circumference, sperm morphology, libido, serving capacity

-no effect on sperm motility

What are long day breeders?

species that breed during lots of daylight/short nights (as with short day breeders, some animals are breeding in off times too)

KNOW THE FIGURE IN 'SEASONALITY' WITH THE PATHWAY FROM LIGHT TO DETERMINING SHORT/LONG DAY CYCLING

it was way too long to attempt to put on here.. it would've been too confusing. But it could be on the test or exam.

How much cooler are scrotal testes than the core body temperature?

4-6 degrees cooler (internal testes are closer to body temp)

Spermatic Cord

-ductus/vas deferens

-testicular artery

-veins of pampiniform plexus

-Cremaster muscle: striated muscle, cannot do sustained contractions, facilitates movement of blood through the pampiniform plexus

Tunica dartos

-in the scrotal skin

-smooth muscle: can sustain contractions for a long period of time

-raises and lowers the testes relative to the body

Pampiniform Plexus

-warm blood comes through the top, but as it gets lower (towards the teste) it cools down (39C -> 33C or 34C)

-veins and arteries are intertwined: heat transfers from the warmest area to the coolest area (artery -> vein)

-COUNTER CURRENT HEAT EXCHANGE (veins and arteries have currents in opposite directions)

What are the 2 regulatory mechanisms for testicular temperature?

- thermosensitive neurons in the scrotal skin

-thermosensitive neurons in hypothalamus

---> these mechanisms occur very quickly

How do the neurons in the scrotal skin regulate temperature?

they detect a rise in temp and send a signal on a neuron to the respiratory centre (in brain stem). A signal gets sent out along another neuron to the respiratory muscles, stimulating those muscle to pant (Polypnea)

How do the neurons in the hypothalamus regulate temperature?

-as blood flows through hypothalamus, if the temp of the blood is considered too high, then the neurons will be stimulated

-a signal is sent down to the sweat glands in the scrotal skin, which produce sweat

What type of cooling is panting and sweating?

Evaoporative cooling