Animal Science: Digestion, Nutrition, Reproduction, and Breeding Systems
Animal Science on GACE Agriculture (709) covers digestive anatomy, nutrient requirements, reproductive cycles, breeding systems and genetic prediction, health, and product quality for cattle, swine, sheep, goats, horses, and poultry. Many items are numeric: feed conversion, ration cost per pound of gain, gestation length.
Digestion
- Ruminants (cattle, sheep, goats, deer) have four compartments: reticulum, rumen, omasum, abomasum. The rumen is the microbial fermentation vat; the abomasum is the true glandular stomach. Rumination and eructation manage gas; trapped gas causes bloat.
- Monogastrics (swine, poultry, dogs) have one stomach. Horses are hindgut fermenters with a functioning cecum. Poultry have no teeth: the crop stores feed, the gizzard grinds it with grit, and feces and urine leave via the cloaca.
Nutrition and feeding
- Protein quality is amino acid profile. Lysine is first-limiting in corn–soy swine diets; methionine is first-limiting in poultry.
- TDN expresses energy; crude fiber is poorly used by poultry and young pigs.
- Feed conversion ratio (FCR) = feed consumed ÷ weight gained. Lower is better.
- Calcium-to-phosphorus balance, salt, and trace minerals matter; drug labels carry withdrawal times.
Reproduction and genetics
- Gestation: cow ~283 days, sow ~114, ewe ~148, mare ~336. Chicken incubation ~21 days; heifer estrous cycle ~21 days.
- Crossbreeding captures heterosis (hybrid vigor); inbreeding raises uniformity but risks inbreeding depression.
- Expected progeny difference (EPD) predicts how a sire's progeny will differ from breed average - it is not the animal's own record.
Worked example
Fifty pigs gain 60 lb each, so total gain = 50 × 60 = 3,000 lb. The pen consumed 8,400 lb of feed. FCR = 8,400 ÷ 3,000 = 2.8:1. If a cheaper ration pushes FCR to 3.2:1, the same 3,000 lb requires 9,600 lb of feed - 1,200 lb more. Compare feed cost per pound of gain, not cost per ton, before switching rations.
Traps that cost marks
- Naming the rumen as the true stomach, or scrambling compartment order.
- Inverting FCR to gain ÷ feed, or claiming a higher FCR is better for feed efficiency.
- Reading an EPD as the bull's own weaning weight.
- Confusing sow and ewe gestation lengths.
- Ignoring withdrawal time when asked whether milk or meat can be sold.