Seasonality and environment

What are the 8 main environmental factors that affect animal performance?

1. Temperature

2. photoperiod

3. humidity

4. stocking density

5. group homogeneity

6. nutrition

7. cleanliness

8. surface traction

What traits are part of "homogeneity of animals in a group"?

1. Size

2. gender

3. species

4. social rank

5. age

6. body weight.

What is photoperiod?

The number of light and dark hours in a 24-hour cycle.

Define a "short day."

More than 12 hours dark, less than 12 hours light (e.g., 8 hours of light).

Define a "long day."

More than 12 hours light, less than 12 hours dark (e.g., 16 hours of light)

How does light affect the pineal gland?

Light inhibits pineal activity, reducing melatonin secretion.

When is melatonin secretion highest?

During nighttime (dark period).

What does melatonin regulate?

Various body functions including reproduction and circadian rhythms.

Which animals are "short-day" breeders

Ewes and Does.

Which animals are "long-day" breeders?

Mares, Cats, and Dogs.

How does melatonin affect breeding in ewes and does?

↑ Melatonin → ↑ GnRH → ↑ LH → Ovulation.

How does melatonin affect breeding in mares?

↓ Melatonin → ↑ GnRH → ↑ LH → Ovulation.

How does a long photoperiod affect lactation?

Increases milk yield, yield persistency, and alters milk composition.

How does a long photoperiod affect cattle growth?

↑ Average daily gain, ↑ carcass protein, ↓ fat, ↓ age at puberty, ↓ hair length.

How does a short photoperiod affect growth?

↑ Carcass fat, ↑ hair length, ↓ mammary development.

What human condition is linked to photoperiod?

Seasonal Affective Disorder (S.A.D.).

What is thermoneutrality?

No net heat gain or loss; minimal energy spent on temperature regulation.

What defines optimal environmental performance?

Environment supports physiological needs without energy wasted on heat production/loss.

List 6 components of the thermal environment.

1. Radiation

2. humidity (water vapor pressure)

3. wind speed

4. air temperature

5. altitude

6. photoperiod.

What aspects of performance are affected by thermal stress?

Appetite, feed efficiency, growth, milk yield, fertility.

What is the main challenge for homeotherms?

Dissipating excess heat.

What part of the brain regulates thermogenesis?

Hypothalamus.

Which neurotransmitters increase or decrease heat production?

• ↑ HP: Norepinephrine

• ↓ HP: Acetylcholine, Serotonin, PGE2

What hormones are calorigenic (increase heat production)?

Thyroxine, Triiodothyronine, Cortisol, Corticosterone, Growth hormone.

What is thermal homeostasis?

Balance between heat production and heat loss

What are passive methods of heat loss?

Conduction, convection, radiation (no energy used).

What are active (evaporative) methods of heat loss?

Panting, sweating (requires energy).

What are physiological adjustments animals make to ambient temperature changes?

• ↑ Respiration (dead space ventilation, uses ATP)

• ↑ Oral/Nasal blood flow

• Changes in cardiac output

• Skin responses

• Scrotal regulation in males