Lecture 26: Sheep Nutrition

sheep feeding behavior

• selective grazers

• adapted to extensive grazing systems

• production phase determines feeding strategy

economics and nutrients of sheep

• feed = 50-70% of cost

• maintenance often met by pasture

• rumen synthesizes vitamins A and K

• vitamin E must be supplemented

• key minerals are I, Se, Cu, Co

total confinement production system

• ewes and lambs housed in dry lots or pens; lambs weaned at 30-45 days

• efficient use of space, close monitoring, supports accelerated lambing

• high feed costs, increased labor, manure management required

semi-confinement production system

• ewes and lambs on pasture early (30-45 days), then lambs weaned and finished in confinement

• combines pasture use with controlled finishing, moderate costs

• requires both pasture and facility management

range/pasture with shelters production system

• ewes graze pasture/range; lambing occurs in shelters or drop pens

• protection during lambing, improved survival in adverse weather

• requires infrastructure; more labor at lambing

range/pasture with no buildings

• ewes live and lamb entirely on pasture/range

• lowest cost system, minimal infrastructure

• higher lamb mortality risk; weather exposure; less control

accelerated lambing systems

• multiple lambing periods per year

• increased productivity

• high nutritional and management demands; requires specific breeds

accelerated lambing systems require breeding how often?

every 6 months → dorset ewes can lamb year round

milk sheep breed

• east friesian

• highest milk-producing breed → use milk for cheese

• very docile, not hardy

cross-bred sheep for meat production

• commercial white-faced ewes crossed with suffolk, hampshire, dorset, southdown, or shropshire ram (terminal sire) → results in sheep with black faces and excellent carcass quality

• lean, gain weight rapidly

wool from cross-bred sheep for meat production

low quality and discounted

milk sheep production

• milk yield: 0.75-2.0 lb/day

• early weaning: 3 days → milk twice daily

• partial suckling: 30 days → milk once daily

what breed of ewes should be used for accelerated lambing programs?

dorset

sheep BCS

• BCS 1 = emaciated → BCS 5 = obese

• assessed at loin (spinous/transverse processes)

• target BCS 3-3.5 at breeding

ewe nutritional phases (annual cycle)

maintenance → breeding (flushing) → gestation → lactation → post-weaning

maintenance period

• dry period

• BCS 2.5-3

• goal is low-cost maintenance feeding

breeding (flushing) phase

• increase intake 4 weeks before breeding

• target BCS: 3-3.5

• goal is to improve ovulation rate and fertility

gestation phase

• early-mid: slight increase in requirements

• late gestation (last 6 weeks): most critical!

• risk is pregnancy toxemia

lactation phase

• highest nutritional demand

• peak milk: 2-3 weeks postpartum

• negative energy balance common

post-weaning phase

• regain lost BW

• restore BCS to 2.5-3

• prepare for next breeding cycle

what are the most nutritionally critical periods?

late gestation and early lactation

maintenance of ewes

• requirements met by pasture

• key management: minerals, water, parasite control

how can you increase intake before breeding?

• turn ewes onto high-quality pasture OR

• supplement with 1/4-1/2 lb grain or pellets/hd/d

target BCS for flushing and breeding

3-3.5

flushing and breeding improves

ovulation rate → improves lambing rate by 10-20%

flushing and breeding response factors

• best in mature ewes → strongest response early or late in the breeding system

• limited in fat ewes

• poor in ewe lambs

• timing: 4 weeks before → 2 weeks after ram

early-mid gestation

slight increase in requirements

late gestation (critical)

• last 6 weeks

• increased fetal growth

• risk: pregnancy toxemia

• poor nutrition → lighter lambs with less energy reserves, uneven birth weights in twins

why should you avoid over- or under-feeding during early to mid gestation?

affects attachment to uterine wall or placenta development

what is the most important feeding period?

gestation

nutritional demands of lactation

• energy = 3x maintenance

• peak milk: 2-3 weeks

• negative energy balance → using body fat for energy and milk, acceptable to lose BCS of 1 during lactation

feeding guidelines for lactation

• DMI: 3.5-4.5% BW

• CP: 13-15%

• grain supplement needed

• adjust for number of lambs

problems with energy in sheep

• pregnancy toxemia → disease of energy metabolism in ewes carrying multiple fetuses

• overfed fat ewes

• hypothermia in newborn lambs

mineral problems in sheep

• iron deficiency in housed lambs

• copper toxicity/poisoning

management related problems for sheep

• castrated male lambs (wethers) susceptible to urolithiasis

• enterotoxemia in growing lambs from clostridium perfringens type D

pregnancy toxemia

• improperly fed in late gestation

• more common in under-conditioned and over-conditioned ewes

• clinical signs include decreased appetite, neurologic signs, recumbency → death

how much does energy need to increase in late gestation to prevent pregnancy toxemia?

• by almost 25% from early to late gestation for single lamb

• energy need increases 35% for twins and 45% for triplets

why is pregnancy toxemia more common in under-conditioned and over-conditioned ewes?

• liver increases gluconeogenesis to meet glucose demands of fetus(es)

• fat mobilization increases → lipolysis → use glycerol → glucose in liver

• can overwhelm liver capacity to process fat → results in hepatic lipidosis and ketosis

triglycerides are composed of

glycerol and 3 fatty acids

when should flushing occur in ewes prior to introduction of the ram?

4 weeks prior

hypothermia in lambs

• high surface area → heat lost quickly

• low fat reserves

• requires early colostrum → generate body heat

care of hypothermic lambs

• thorough warming

• administration of glucose into peritoneal cavity

nutritional needs for nursing lambs

• high energy demand

• vitamin E important → 50% of energy intake from fat

• iron deficiency can occur in housed lambs (confined need iron support)

feeding development of nursing lambs

• creep feed: 16-20%

• intake begins at 3-4 weeks → important for rumen development

acute copper toxicity/poisoning

• accidental administration

• excessive soluble copper salts → anthelmintic drenches, mineral mixes, or improperly formulated rations

primary chronic copper toxicity/poisoning

• excessive copper consumption over extended period

• subclinical until copper stored in liver released when sheep are stressed

secondary copper toxicity/poisoning

phytogenous poisoning after ingestion of plants causing mineral imbalances → excessive copper retention

causes of urolithiasis

• high grain diets

• low Ca:P or high Mg

• low water intake

• wethers castrated early

prevention of urolithiasis

• correct Ca:P (2:1)

• water availability

• urinary acidifiers

growing lambs

• 45-80lbs

• ADG: 0.5-0.8 lb/day

• CP: 14-16%

finishing lambs

• high-energy diet

• risk: enterotoxemia, urolithiasis