light

what is light?

electromagnetic radiation, with visible light being a small portion of the full spectrum

what wavelength is range is visible light?

~380–780 nanometers (nm)

does light appear the same to all animals?

no, animals perceive light differently than humans

what determines the light emitted by an object?

its temperature

what are the two ways animals respond to light?

indirect and direct response

what is the indirect response?

eye → nerve → brain → target organ

what is the direct response?

-light can pass through semitransparent “windows” in the skull and reach the brain

-brain is directly stimulated by light

what are extra-retinal receptors?

-important endocrine glands

-glands that secrete hormones directly into blood

which glands are involved in light perception?

pineal gland and hypothalamus

what are photoreceptors?

cells in the retina that detect light

what are rods used for?

low-light (night) vision

what are cones used for?

daylight and color vision

what is photopic vision and who uses it?

use of cones; birds

what is scotopic vision and who uses it?

use of rods; mammals

what are biological rhythms?

regular changes in body functions over time

what are examples of biological rhythms?

-body temperature

-hormone levels

-reproductive cycles

-behavior patterns

what are the two main types of rhythms?

seasonal and diurnal

what is photoperiodism?

changes in animal function based on day length

which animals are most affected by photoperiodism?

birds (more than mammals)

what is seasonal breeding?

-predominantly spring/fall

-induced by day length (photoperiodism)

-followed by period of repro quiescence with decreasing/increasing day length

what does diurnal mean?

-active during day/night, inactive vice versa

-activity recurs predictably according to 24-hour cycle

-daily light/darkness cycle strongest environmental stimulus for timing of behavior

what is the strongest environmental cue for behavior timing?

light/dark cycle

what hormone does the pineal gland produce?

melatonin

what regulates melatonin?

darkness (light suppresses it)

what does melatonin control?

-circadian rhythm

-sleep

-body temp

-stress and immunity

what hormone is released by the hypothalamus?

gonadotropin releasing hormone (GRH)

what hormones does the pituitary release?

-FSH → follicle stimulating hormone

-LH → luteinizing hormone

are poultry long-day or short-day breeders?

long-day breeders

what is the critical day length for poultry reproduction?

11–13 hours

what does increasing day length do in poultry?

simulates reproduction and egg production

how does lighting affect poultry production?

-age at sexual maturity

-egg size

-egg production length

-body weight

what happens if photoperiod decreases during growth?

sexual maturity is delayed

why should light not increase too early in pullets?

it causes early maturity and small eggs

when should lighting increase for laying hens?

around 16–20 weeks of age

how does extended light affect cattle growth?

can increase growth up to ~10%

how does light affect pigs?

no major benefit from extended photoperiod

how does light affect sheep growth?

increased weight gain with longer light periods

how does light affect puberty in animals?

-can accelerate or delay puberty depending on species

-long days may delay reproduction in some species

what is color in terms of light?

wavelength

what colors are cattle most sensitive to?

yellow-green and blue-purple

can poultry see UV light?

yes they can

how does light color affect poultry behavior?

-blue/green → calmer, better growth

-red/yellow → increased activity

what is light intensity?

brightness of light

how does high light intensity affect animals?

increases activity

why is minimum light intensity important?

-stimulates brain/hormones

-supports welfare

-allows workers to see

what units measure light intensity?

lux (lx) and foot-candles (fc)

what is a lumen?

measurement of light output from a bulb

minimum light for cattle?

~70 lux

minimum light for lambing?

~170 lux

light for chicks?

20–55 lux

light for adult broilers?

~1 lux

light for egg-laying hens?

5–10 lux

why must light intensity be limited in lab animals?

to prevent eye damage (phototoxicity)

recommended max for rodents?

less than ~25 foot-candles (~325 lux upper safe range)

what are common types of lighting used?

-incandescent

-fluorescent

-cold cathode

-LED

which lighting type is most efficient and long-lasting?

LED

what is a dimmer?

device used to control light intensity

benefits of dimming in poultry?

-reduces activity

-improves feed efficiency

-saves energy

what are the three key lighting factors?

-photoperiod (duration)

-intensity (brightness)

-color (wavelength)

how is lighting managed in facilities?

-selecting proper bulbs

-adjusting intensity (dimming)

-controlling photoperiod (timers)

what is the most important role of light in animals?

regulating biological rhythms and physiological processes

what systems are most affected by light?

-reproduction

-growth

-behavior

-hormones