Livestock Update, November 1999
Scott Greiner, Extension Animal Scientist, Sheep, Virginia Tech
Management of the Gestating Ewe
As fall progresses, winter and spring-lambing ewes will make the transition from pasture to a diet of harvested feedstuffs. Adequate nutrition during gestation is critical for a healthy, vigorous lamb crop. At the same time, many ewes are overfed during early and mid-gestation, resulting in high feed costs. There is a relatively small increase in ewe nutrient requirements for the first 15 weeks of gestation compared to maintenance. As pastures become short and feeding hay becomes necessary, it is important that both the quality and quantity of hay being fed be closely considered. Assuming the available hay is 50% TDN and above 10% crude protein on as as-fed basis, a 175 lb. ewe eating 3.3 lbs./day of this hay would easily meet nutrient requirements during early pregnancy (Table 1). If hay is fed free-choice, most ewes of this size have the appetite to consume considerably more than 3.3 lbs./day. For this reason, average quality hays (grass-mix) should be fed during this stage of production. High quality hays such as alfalfa should be reserved for feeding during lactation when nutrient requirements increase due to milk production. If high quality hays need to be fed during early gestation, it is important to limit intakes. Overfeeding during this period is costly, and ewes that become excessively fat early in pregnancy have more problems with ketosis if the high plane of nutrition is not continued through lambing.
Approximately 2/3 of the birth weight of a developing fetus is gained during the last six weeks of gestation. As a result, the nutritional requirement of the ewe for both energy and protein increases. Table 2 shows that TDN requirements increase to 57-66%, compared to 55% for maintenance and early gestation. Similarly, protein requirement increases to around 11% compared to 9% for maintenance. The most critical difference is the increase in energy requirement. Inadequate nutrition during this period may result in pregnancy ketosis, light birth weights, weak lambs, and lower milk production. Supplementation of 1 to 2 lb. corn/ewe/day, in combination with average to good quality hay (> 11% CP) should provide adequate nutrition. An important consideration during this period is the number of fetuses the ewes are carrying (see Table 1). As the ewes approach lambing, the size of the uterus increases and limits intake. Therefore, feeding nutrient-dense rations in important to ensure adequate nutrition. Although corn silage is an excellent feed for sheep, its high moisture content and bulkiness prevents it from being the sole roughage source during late gestation. Additionally, corn silage is low in protein and calcium and requires additional sources of these nutrients be added to the diet for balanced nutrition.
Many producers are probably tight on hay supplies, and therefore may want to consider substituting corn for hay this winter. To make this decision, corn and hay must be compared on a cost per pound of TDN. If corn is $2.80/bu. ($100/ton), each lb. of TDN from corn costs $.065. Assuming available hay is approximately 50% TDN, corn would be a cheaper source of energy if hay is more than $65/ton. When consideration is made that there will be approximately 5% of the hay wasted, the price that can be paid for the hay is only $61/ton to make it equivalent to $100/ton corn on an energy basis. As a general rule of thumb, one pound of corn is roughly equivalent to two pounds of hay on an energy basis. Ewes should receive a minimum of 40% of the ration as roughage to prevent rumen upset and wool picking.
Other important management considerations during gestation include a solid health program. Four weeks prior to lambing, ewes should receive booster vaccinations for overeating and tetanus. Vaccination at this time will provide immunity to the lambs through colostrum at birth. Selenium supplementation is suggested for Virginia flocks. Ewes should be provided selenium supplementation 8-10 weeks prior to lambing. Selenium can be provided through salt-mineral mixes specifically formulated for sheep. If supplementation through a salt-mineral mix, ewes can be administered 2.5 to 3.0 mg injectable selenium four weeks prior to lambing. Dosage should be carefully calculated, as high levels of selenium are toxic. Vaccines for prevention of abortion diseases (vibrio and chlamydiosis) have not been widely available. Chlortetracycline (Aureomycin) fed at a level of 80 mg/head/day (approved dosage) during the last six weeks of gestation has been shown to aid in prevention of these diseases. Injections of oxytetracycline (LA 200) at 2 week intervals the last 4-6 weeks of gestation have also been recommended as a preventative measure. Ewes should be dewormed 2 weeks prior to lambing. Research has documented that worms increase egg shedding just prior to and continuing after lambing. During this time, the ewe has a reduced ability to deal with the increased worm load. Therefore, deworming prior to lambing is an important aspect in an effective parasite control program.
Table 1. Daily Nutrient Requirements of Mature Ewesa
Stage of Production
|1st 15 wk. gestation||150|
|Last 4 wk. gestation|
(130-150% lamb crop)
|(180-225% lamb crop)||150|