Feeding Sheep: ANFS 251 Animal Nutrition

Animal Nutrition: The Plan

  • Nutrient requirements depend on the animal's life cycle and production stage.
  • Sheep are ruminant herbivores.

Sheep Nutrition Challenge

  • Goal: Identify the optimal level of nutritional management for optimum production.
  • Optimum production is not maximum production, nor is it production at minimum cost.
  • Take advantage of compensatory growth during seasonal forage changes.
  • Maintain energy status from one production cycle to the next.

Nutrition and Sheep

  • About 5% of ewes fail to lamb, and 15-20% of lambs die between birth and weaning.
  • Nutrition is a major contributing factor to these losses.
  • Supplying nutrient needs is the single largest expense in raising sheep.

Body Condition Scoring

  • Body composition influences a ewe's response to nutrition levels.
  • Body weight and condition scores help producers make feeding decisions.
  • Body condition scoring helps determine the quality and quantity of feed needed for optimal performance.

Optimum Feeding Systems

  • Range from intensive feeding of confined sheep to supplementation of flocks mainly dependent on range forage.

Optimum Feeding Systems: After Weaning

  • Nutrition is important for replenishing body reserves and preparing for the next production cycle.

Ewe Biological Cycle

  • Feeding systems involve periods of both nutrient surplus and deficit relative to requirements.
  • Goal: Maintain a balanced body composition over the yearly biological cycle.
  • A ewe's cycle can be divided into periods with different nutritional needs.

Weight Changes

  • Weight changes expected in a 150-lb ewe throughout the different stages of her yearly production or biological cycle.

Breeding and Flushing

  • Flushing: Increasing the intake of ewes prior to and during mating.
  • Purpose: To increase ovulation and lambing rate.
  • Method: Turning ewes onto lush, high-quality pasture before breeding.
  • Alternative: Supplementing with 1/4 to 1/2 lb of grain or pellets per head per day.
  • Timing: Usually begins about 2 weeks before joining with rams and continues for 2-3 weeks into the breeding season.

Response to Flushing

  • Mature ewes respond better to flushing than yearlings.
  • Fat ewes may not respond to flushing.
  • Flushing generally leads to more eggs being shed and higher lambing rates.

Gestation

  • Poor nutrition can lead to lamb deaths before, during, and soon after lambing.
  • Cold weather is often blamed, but inadequate nutrition is a major factor.
  • The ewe must be fed enough to meet requirements for maintenance, fleece production, fetal and associated tissue development, and growth.

Gestation: Critical Time Periods

  • Critical periods for placental development, fetal growth, and mammary gland development occur between day 30 & day 90, after day 90, & after day 120 of pregnancy.

Gestation

  • Fetal growth is minimal during the first 15 weeks of pregnancy.
  • Extremes in nutrition (under- or overfeeding) during this period are detrimental.
  • Majority of placental development occurs during this period (day 30 to 90 of pregnancy).
  • Poor placental development results in lower fetal growth rates and reduced lamb survival rates.

Gestation: Last 6 Weeks

  • The last 6 weeks of gestation are the most critical period in ewe nutrition.
  • Approximately 70% of fetal growth occurs at this time.
  • Severe undernutrition leads to:
    • Pregnancy toxemia and possibly ewe death
    • Lowered birth weights
    • A major factor affecting lamb mortality

Singles versus Twins

  • Poor nutrition in late pregnancy causes:
    • Lighter lambs at birth
    • Uneven birth weights in twin/triplet lambs
    • Reduced wool follicle development
    • Lower energy reserves in newborn lambs

Birth Weight and Mortality

  • Birth weight is a major factor in lamb mortality.
  • Birth weights vary from 3.5 to 20 lb.
  • Differences are associated with breed, dam's age & litter size, but also greatly depend on ewe nutrition & energy intake during the last month of pregnancy.

Gestation: Excessive Feeding

  • Excessive feeding may result in lambs with increased birth weights, leading to lambing difficulties.
  • Efficiency of converting dietary energy to energy gain in the fetus is only about 13%.
  • Ewes in late pregnancy require 50% more feed if bearing a single lamb, and about 75% more if bearing twins.
  • Limit to the extent to which body fat reserves can be utilized during this period.
  • Excessive fat mobilization causes pregnancy toxemia.

Parturition

  • Good-quality forage and plenty of fresh water are generally recommended.
  • Start feeding grain or supplement about 12 to 24 hours after lambing.

Lactation

  • Takes ewes several days to reach maximum milk production, and for their lambs to consume large quantities of milk.
  • A ewe usually reaches maximum milk production by 2 to 3 weeks after parturition.
  • Milk production generally declines fairly rapidly thereafter.

Singles versus Multiples

  • Single lambs: Ewe adjusts production downward to the level the lamb is consuming.
  • Ewes nursing multiple lambs produce 20% to 40% more milk than those nursing singles, and thus have greater nutritional requirements.

Singles versus Multiples

  • Separate ewes with multiples from ewes with singles.
  • Feed each according to their nutritional needs for maximum rate and efficiency of lamb gains.

Lactation

  • Milk is critical in the first 3 to 4 weeks of the lamb's life.
  • Correlation between milk intake and live-weight gain is approximately 0.90 in this period.
  • Lambs receiving inadequate amounts of milk can compensate some by increased feed consumption.
  • To prevent loss of body tissue, daily intakes of ME energy are three times maintenance – seldom achieved ME.

Lactation

  • A ewe's requirements during this period can usually be met by good-quality pasture or range.
  • Early lactation: Body fat can be safely used to meet some of the high-energy demands.
  • Milk production of minor importance after 8 to 10 weeks.

Post-weaning

  • Body condition can be adjusted so that ewes are in appropriate body condition at breeding.
  • Most ewes are overfed during this period so they gain back the weight lost during lactation.
  • Desirable to utilize poor-quality pasture or feed during this period, saving better-quality forage for periods of the production cycle that are nutritionally more critical.

Sum it Up!

  • Ewe nutrition is strongly influenced by number of offspring.
  • Sheep nutrition is forage based.
  • Matching forage production with biology will help reduce need for supplementary feed.
  • The use of supplements should be strategic.

More on Sheep

  • Nutrient requirements depend on what they are doing (Life Cycle Nutrition).