Lecture 21 – Beef Cattle Nutrition

Where are beef cows primarily maintained?

On pasture, making use of forages and by-products that would otherwise go to waste.

How many calves is a beef cow expected to produce each year?

One calf per year.

What is the average birth weight of a calf?

40–50 kg.

When are cows re-bred after calving?

Within 60–90 days to maintain a yearly calving cycle.

How long is bovine gestation?

About 9 months.

How long do calves nurse?

About 7 months, while also grazing and sometimes receiving creep feed.

When are most calves born?

In the spring or fall.

What share of global cattle and beef does the U.S. produce?

~7 % of the world’s cattle but ~20 % of the world’s beef/veal.

Where are most U.S. beef cattle located?

West of the Mississippi River, especially Texas to South Dakota and the Southeast.

Structure of the Beef Industry

What is the overall goal of the beef industry?

To produce heavier animals at the lowest cost.

List the four main phases of the beef industry.

Cow-calf, Stocker/Yearling, Feedlot (Finishing), Packing Plant (Slaughterhouse).

At what weight and age are calves sold at weaning?

300–700 lb, 6–10 months old.

At what weight do cattle enter and leave the feedlot?

Enter 600–800 lb; finish 900–1400 lb.

How long do cattle stay in feedlots?

About 4–5 months.

Feeding the Brood Cow – Postpartum

How long is the postpartum period?

80–90 days after calving.

Why is this the period of greatest nutritional demand?

The cow must lactate, repair tissues, resume cycling, re-breed, and possibly continue growing.

What is essential during postpartum?

Adequate fresh forage, optional grain for extra energy, and mineral supplementation.

What happens if nutrient needs aren’t met?

Delayed breeding, weight loss, or reproductive failure.

Feeding the Brood Cow – Lactating and Pregnant

When does this stage occur?

First 120–130 days after calving until weaning.

How do nutrient needs compare with postpartum?

Energy needs ↓ 13 %, protein needs ↓ 8 %.

Why are nutrient needs still high?

The cow is lactating and active; young cows are still growing.

Do cows usually gain or lose weight in this period?

They typically lose some weight.

Feeding the Brood Cow – Gestation

What stage is this?

100 days after weaning, the second trimester of pregnancy.

How do energy and protein needs change?

Energy ↓ 23 %, protein ↓ 36 % from previous stage.

Why is this stage important for body condition?

It’s the best time to regain weight and improve body condition.

How much should heifers gain daily?

About 1–1.5 lb per day.

Feeding the Brood Cow – Pre-Calving

When does this occur?

50–60 days before calving (third trimester).

Why is this period critical?

Cows must calve in good body condition (BCS 3–4 of 5) for healthy calves and rapid re-breeding.

How much do energy and protein needs rise?

By 20 % + compared to gestation.

Expected daily gains?

Cows 1–1¼ lb/day; heifers 2–2½ lb/day.

How much weight can the fetus gain?

Up to 60 lb.

Why may intake decline late in pregnancy?

The growing fetus reduces rumen space.

Feeding the Lactating Cow and Calf

How soon must the calf receive colostrum?

Within the first 24 hours.

How long does the calf nurse on a cow-calf operation?

6–7 months.

What is creep feeding?

Supplying extra feed to nursing calves for added nutrients.

List advantages of creep feeding.

Heavier calves at weaning, better uniformity, easier weaning, less dam weight loss.

List disadvantages of creep feeding.

High cost, extra labor, not suitable for replacement heifers (risk of over-fatness).

Feeding the Weaned Bovine (Finishing Phase)

What happens after weaning?

Calves enter feedlots to be fed to market weight.

Do heifers or steers reach market weight first?

Heifers reach market grade at lighter weights.

What percent body fat is typical at finishing?

About 30 %.

What type of diet is fed?

High-grain, energy-dense diet for rapid gain.

Why must animals be adapted gradually to feedlot diets?

To prevent rumen acidosis.

Market weight of finished beef cattle?

400–500 kg.

Feeding the Bull

How does a mature bull’s nutrient need compare to a cow’s?

Needs about 15 % more.

What if a bull’s BCS drops too low?

Provide supplements, especially in fall/winter.

What do young bulls require?

More grain and protein for growth to breeding condition.

What is the target body condition score for breeding bulls?

About 6 of 9.

Nutrition Issue – Bloat

What causes bloat?

Inability to expel rumen gases produced by microbial fermentation.

What happens if bloat is severe?

Rumen pressure compresses lungs/diaphragm → suffocation within 1 hour.

Name the three types of bloat.

Frothy feedlot bloat, Frothy pasture/legume bloat, Free-gas bloat.

What causes frothy feedlot bloat?

Stable foam from high-grain diets covering the cardia.

What causes frothy pasture bloat?

High-protein legumes such as alfalfa, clover, winter wheat.

What legumes are rarely associated with bloat?

Tannin-containing legumes (arrowleaf, berseem, birdsfoot, tropical legumes).

List clinical signs of bloat.

Left-side swelling, discomfort, kicking at flank, stomping, possible sudden death.

How to prevent bloat on lush pasture?

Feed hay first, avoid turning out hungry cattle, adapt to grain slowly.

What drug breaks down rumen foam?

Poloxalene, administered via stomach tube.

What roughage level helps prevent bloat in feedlot diets?

10–15 % coarsely chopped roughage.

What is a last-resort treatment for severe bloat?

Trocar or bloat needle to release gas (infection risk).

Nutrition Issue – Rumen Acidosis

What causes acidosis?

Sudden diet shift from forage to high-starch concentrates or overfeeding grain.

Normal rumen pH?

6–7 on forage diets.

Rumen pH during acidosis?

Falls to 5–6 or lower.

What microbes increase at low pH?

Lactic-acid-producing bacteria.

Complications from chronic acidosis?

Laminitis, liver abscesses, rumen wall lesions, polioencephalomalacia.

List clinical signs of acidosis.

Rumen stasis, diarrhea, dehydration, weakness, gray foamy manure, anorexia.

Define subacute acidosis.

pH < 5.6 – variable intake and poor gains.

Define acute acidosis.

pH < 5.2 – heart/lung failure, death.

How to prevent acidosis?

Gradually introduce grain over 3–4 weeks, keep ≥ 10 % roughage, feed effective fiber, mix grain types, avoid over-processing.

Which feed additives help prevent acidosis?

Ionophores such as Monensin or Lasalocid.

Nutrition Issue – Grass Tetany

What causes grass tetany?

Low magnesium and calcium in rapidly growing or Mg-deficient forages.

Which animals are most susceptible?

Lactating, high-producing cows.

List clinical signs of grass tetany.

Nervousness, muscle twitching, staggering, convulsions, collapse, death if untreated.

How is grass tetany treated?

Slow IV of 500 mL calcium-borogluconate with 5 % magnesium hypophosphate, followed by oral Ca–P–Mg–K gel.

How to prevent grass tetany?

Apply dolomitic lime to soils, feed high-Mg minerals starting 1 month before season, add legumes, and improve phosphorus fertilization.

Which forages are naturally high in magnesium?

Legumes such as alfalfa and clover.