March 2009 Articles

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Nutrition Key for Conception and Weaning Percentages

Nutrition Key for Conception and Weaning Percentages Steven M. Jones, Associate Professor - Animal Science
The success of a sheep and goat operation depends on the number of lambs and kids raised, weaned and marketed each year. The percentage of ewes, does, ewe lambs and doelings conceived early in the breeding season; the lambing, kidding and weaning percentages; and the percentage of ewes, does, ewe lambs and doelings lambing and kidding unassisted are some of the most important factors influencing profits in the sheep and goat business. In other words, production is equal to reproduction.
Most small ruminants are known as seasonal breeders – the female only cycles and accepts the male during times of shortening day length. Cycling usually initiates by the end of August to early September through February. If not bred, does/ewes will cycle every 21 days, similar to cows. There fore, does/ewes should become pregnant within 4 weeks following the introduction of bucks with the herd. The gestation length (time from breeding to kidding/lambing) averages 150 days (5 months). Yearlings may be bred in the first year at 7 to 10 months of age, depending on breed, if they have grown well and are of good size and condition. Body weight, relative to breed, is more important than age and can influence lifetime performance.
The nutritional status of a herd is the most important factor influencing reproduction. It is also the factor over which the producer has the most control by either increasing or reducing nutrient consumption. The body condition of a ewe or doe strongly affects the following:
the time at which puberty starts
the conception rate at first estrus in ewe lambs and doelings
the length of the postpartum interval
the health and vigor of newborn lambs and kids
The practice of increasing nutrient intake and body condition prior to and during breeding is called flushing. Its purpose is to increase the rate of ovulation and, thus, lambing or kidding rate. Flushing is especially beneficial for thin females that have not recovered from previous nutritional stresses such as poor forage quality, parasite infection, lactation or disease. Flushing can be accomplished by providing ewes or does with high quality pasture, supplemental harvested forage or grain, depending on environmental stress, availability of forage and body condition of the ewe.
Warm-season forages, such as bermudagrass or crabgrass, are an option for providing nutrition for flushing in late summer in Arkansas. They need to be fertilized and managed for appropriate volume and quality needed for flushing. Forage brassicas are one cool-season forage option available for early fall (October). Demonstration projects in Arkansas have shown that forage may be available 45 to 60 days after planting that will yield crude protein ranging from 18 to 33 percent and TDN ranging from 72 to 89 percent. The seeding cost for brassicas with annual ryegrass will be about $21 to $25 per acre. Expected yield for initial grazing will be 2.25 to 2.5 tons of dry matter per acre.
Flush feeding usually begins around 2 weeks prior to breeding and continues at least 2 to 4 weeks into the breeding season. This ensures good embryo attachment to the uterus wall, reducing early embryonic death.
Body condition or changes in body condition before and during the breeding season affect reproductive performance in terms of services per conception, lambing and kidding intervals and the percentages of open ewes and does. Ewes and does should be in good body condition at lambing and kidding and should maintain good body condition during the breeding season. Bucks and rams should also be evaluated for proper body condition. Source: University of Arkansas