Lecture 22- Beef Cattle Nutrition 2

How does cold stress affect nutrient needs?

Increases energy requirements beyond maintenance.

What is effective temperature?

Air temp adjusted for moisture + wind; determines cold stress.

What is the lower critical temperature (LCT)?

Temperature below which energy needs increase.

How much does energy requirement increase below LCT (dry coat)?

+1% per degree below LCT.

How much does energy requirement increase below LCT (wet coat)?

+2% per degree below LCT.

What is the LCT for a wet/summer coat?

59°F.

What is the LCT for a fall coat?

45°F.

What is the LCT for a winter coat?

32°F.

What is the LCT for a heavy winter coat?

18°F.

Why do cows need BCS 5-6 going into winter?

Provides insulation and energy reserves for cold stress.

How does diet type affect cold tolerance?

Forages produce more heat; grains provide higher energy density but less heat increment.

What is the BCS scale for beef cattle?

1-9 scale.

What is the target BCS at breeding and calving?

5-7.

What is the ideal BCS for heifers?

6.

How does BCS affect reproduction?

Higher BCS → shorter postpartum interval, better colostrum, improved calf IgG.

Why is BCS better than BW?

BW fluctuates with gut fill; BCS reflects true fat reserves.

How does BCS affect postpartum interval?

BCS 3 = 89 days; BCS 6 = 52 days; BCS 7 = 31 days.

How does BCS affect calf immunity?

Higher BCS → higher colostrum IgG → higher calf serum IgG.

What happens with low or high BCS?

Reduced pregnancy rate.

Why group cows by BCS after calving?

Allows targeted feeding to regain condition.

What is the target heifer weight at breeding?

65% of mature BW.

What is the target heifer weight at calving?

85% of mature BW.

What is the most important factor affecting puberty?

Body weight.

Example: If mature BW = 1100 lb, what is target breeding weight?

715 lb.

Example: If mature BW = 1100 lb, what is target calving weight?

935 lb.

What are key heifer nutrition principles?

Avoid overfeeding energy; ~11% CP; NEg based on ADG target.

What is preconditioning?

Management to reduce stress and disease before feedlot entry.

What are components of preconditioning?

Castration, dehorning, deworming, 2 rounds MLV respiratory + clostridial vaccines, bunk training, 30-45 day low‑stress weaning.

What is the value of a preconditioned calf?

Typically +$30 per calf.

Where should injections be given?

Front of shoulder to avoid muscle blemishes.

When do stockers need energy supplementation?

ADG >0.5 lb/day, low‑quality hay, winter or late summer.

What is typical grain supplementation for stockers?

1-2.5 lb/day.

What CP level is needed to maintain rumen microbes?

>8% CP.

What CP level is needed for stocker growth?

12-16% CP.

When is urea supplementation appropriate?

High‑energy diets; NOT high‑forage diets.

Why does urea not work with high‑forage diets?

Forage digests too slowly for microbes to use urea effectively.

What is the typical feedlot entry weight?

700-800 lb.

What are feedlot diet risks?

Acidosis, laminitis, liver abscesses.

What is feedlot CP requirement?

9-14% CP (higher early, lower in finishing).

Why supplement calcium in feedlot diets?

Grains are low in Ca.

What is the goal of feedlot diet transition?

Adapt rumen microbes from forage → starch over 3-4 weeks.

What is the starting vs final concentrate percentage?

Start 40% concentrate → end 80-90% concentrate.

Why is gradual transition important?

Prevents acidosis and maintains intake.

What is key feedbunk management principle?

Consistency; feed fresh and on time; monitor intake; leave slight orts.

What CP level should growing stockers receive?

12-16%.

What mineral deficiency causes grass tetany?

Mg deficiency (low in spring grass; high K interferes with Mg absorption).

What causes urinary calculi?

High‑grain diets high in P; Ca:P imbalance.

What causes nitrate toxicity?

High nitrate forages (fertilized pastures, weeds); nitrate → nitrite → methemoglobin.

What are signs of mycotoxin exposure?

Reduced DMI, poor growth; calves most sensitive.

What causes sulfur toxicity?

High sulfur feeds (distiller's grains).

What disease results from sulfur toxicity?

Sulfur‑associated polioencephalomalacia.

What is normal vs toxic sulfur level?

Normal 0.18-0.24%; toxic 0.4-0.5%.

What is the mechanism of sulfur‑associated PEM?

High sulfur increases thiamine demand → secondary thiamine deficiency.

What is the time course of sulfur‑associated PEM?

1-4 weeks.

What do hormonal implants do?

Increase ADG by 15-20%.

What are estrogenic implants?

Estradiol, progesterone, zeranol.

What are androgenic implants?

Testosterone, trenbolone acetate.

What does MGA do?

Melengestrol acetate suppresses estrus in heifers.

What do beta‑agonists do?

Shift nutrients toward muscle deposition (e.g., ractopamine/Optaflexx).

What do coccidiostats do?

Control coccidiosis; improve ADG and feed efficiency.

What do ionophores do?

Shift rumen fermentation toward propionate; decrease acetate/methane; improve feed efficiency; reduce acidosis.

What is the key summary of Beef Nutrition 2?

Environment + BCS drive requirements; nutrition varies by stage; feedlot transitions must be gradual; many diseases are preventable with proper nutrition.