Reproductive Management of Herd Sires

By

Paul Coe, DVM

Michigan State University

Basic Needs

Nutrition Shelter Exercise Medical Care Breeding Management

Nutrition

• NRC recommendations provide a guideline– Modify diet based on BCS

• Bulls have two nutritional seasons– Breeding season: maintenance + increased activity

– Post-breeding: maintenance + reconditioning

• Need to start the breeding season at BCS 5 to 6– Variation either way reduces libido and fertility (%

normal sperm)

Body Condition Score and BSE Pass Rate

Condition Score

>6

6

5

4

<4

Barling,Wilkes et.al1995

% Passing

62

67

72

70

55

Diet During Breeding Season

• Grass

• Limiting Nutrients– Fiber (based on 30% dry matter in pasture)– Crude Protein– Phosphorous

How Much Grass Does A Bull Need?

Type Wt. ADG Maintenance DietLarge Frame 2400 0 132 lb.early vegetative

grass

Continental

Moderate Frame 2000 0 110 lb.early vegetative grass

English

Large Frame 1500 2 lb./day 56 lb. Grass + 12 lb. Corn

Yearling

Moderate Frame 1500 2 lb./day 67 lb. Grass + 10 lb. Corn

Yearling

How Much Grass Will A Bull Eat?

• Varies with availability and quality– 75% variation due to availability

– 25% variation due to quality

• 2% of body wt. in dm.needed for maint.– 2400 lb. Large frame bull

• 2400x.02=48 lb./.3(dm in grass)=160 lb. of pasture

• 3% of body wt. In dm.needed for av.growth– 1500 lb. Yearling bull gaining 2 lb./day

• 1500x.03=45 lb./.3(dm in grass)=150 lb. of pasture

The Question

• Does a good bull take the time to eat that much grass when he is checking for heat and breeding cows?

The Answer

• Bulls often lose 1 to 2 body condition scores (160 to 200 lbs) during a breeding season

• Under extensive or rotational grazing management, grass does not stay in the early vegetative state over the breeding season (so consumption goes down).

• The answer is NO.

Diet During the Off Season

• Mature Bulls– Regain lost weight– Regain BCS 5 to 6 through the winter

• Yearling Bulls– Additional growth

• Typical Feeds– Hay and/or silage, grain, mineral.

How much feed does a bull need when he is not breeding cows?

• 270 day feeding period, some cold stress, BCS 4• Large frame mature bull (2400 lb.BCS 5-6)

– 30 lb.grass hay + 9 lb. sh.corn to gain 1 lb./day

• Moderate frame mature bull (2000 lb.BCS 5-6)– 23 lb.grass hay + 9 lb. sh.corn to gain 1 lb./day

• Large frame yearling (from 1400 lb.to 2000 lb.)– 9 lb.grass hay + 19 lb. sh.corn to gain 2.1 lb./day

• Moderate frame yearling bull (1400 lb.to 1800 lb.)– 16 lb.grass hay + 12.5 lb sh.corn to gain 1.5 lb./day

Feeding Bulls

• Assess BCS following breeding season• Analyze available feeds• Plan a ration that should have bulls at BCS

6 for breeding season• Monitor body condition and adjust ration • Hand feeding during breeding season

– Allows daily observation and makes bulls easier to manage

Whole Cottonseed

• Contains gossypol, a toxin that impairs sperm production

• Limit cottonseed to 4 lb./head/day

• Add 4000 IU of vitamin E/head/day to neutralize the effects of gossypol.

Shelter

• Well fed bulls do not need much shelter– Windbreak

• Access to sod/dirt lot improves foot health

• Mud and concrete = feet and leg problems

Exercise

• Maintains physical conditioning for breeding season.

• 2 acres per bull.

• Feed and water spaced apart so that bulls have to walk daily.

Routine Health Care

• Observe frequently during breeding season– Mating ability– Injuries – diagnose and correct promptly

• Close exam at end of each breeding season– Injuries– Body Condition Score– Culture for Trichmoniasis

Breeding Soundness Exam

• Rigorous exam at purchase

• Annual examinations– Aid culling decisions– Prognosis based on evidence of testicle damage

seen in sperm morphology

Disease Control

• Vaccination program same as cows– IBR, BVD, Leptospirosis– Local diseases (Clostridia)– Herd problems (Campylobacter, H. somnus)– Avoid MLV in bulls collected for A.I. Or within 30

days of breeding season

• Parasite control– Deworm with cows– Control liver flukes, if problem exists in herd– External parasites in the fall

Breeding Season Management

• Start with bulls that pass a BSE

• Large testicles increase serving capacity

• Libido and ability to mate– Serving capacity test– Observation– % calf crop attributable to each bull

Bull to Cow Ratio Guidelines

Breeding PlanYearling bull,Conventional Mating

Estrus Synch. with natural service

Cleanup following A.I. **

Rugged terrain, low stocking rate

Mature bull, conventional mating**Assumes AI conception >60%

Ratio*1:25

1:25

1:60

1:35

1:40*Using bulls that passed BSE