Monitor Body Condition Scoring and Nutrition throughout Pregnancy
Producers should strive to meet their sheep's nutritional requirements regardless of the time of year. Nutrition becomes even more important during the breeding season and throughout pregnancy. Nutrition impacts body condition scores, which in turn affect ovulation rates, and nutrition also plays a crucial role in embryonic survival. Throughout pregnancy, body condition scores and nutrition can impact the health and vigor of newborn lambs, as well as colostrum quality and quantity.
Producers score sheep body condition using a 5-point scale: 1 indicates an emaciated sheep, 3 indicates average body condition, and 5 indicates an obese sheep. The optimum body condition score for ewes during breeding is 3, while the optimum body condition score for ewes at lambing is slightly higher. The higher score takes into account the fact that most ewes lose body condition during lactation. However, a slightly lower score at the start of the breeding season and an increasing plane of nutrition will flush the ewes to encourage a higher ovulation rate.
To improve the body condition scores of thin ewes, a suitable goal would be to increase body weight by 10% over 100 days. A good balance might mean that producers strive to have their ewe flock at slightly below a body condition score of 3 at the start of the breeding season in order to take advantage of flushing to increase lambing percentage. All ewes should gradually gain weight so that by the time they lamb, they have reached a body condition score slightly higher than 3.
In addition to body condition scores, producers should manage the body weight of young ewes. Yearlings should weigh at least 80% of their mature weight by the start of the breeding season, and ewe lambs should weigh 65 to 70% of their mature weight. For ewe lambs to reach this desired weight, most will require a grain supplement. In general, sheep gain approximately a quarter to a third of a pound per day on pasture. This rate of gain results in ewe lambs weighing less than recommended for breeding. Therefore, producers should calculate the weight gain required and adjust rations to accommodate a faster rate of gain. Young ewes also need to continue gaining weight throughout pregnancy to account for their own continued growth, as well as the growth of the fetus.
Maintaining body condition scores, or improving those for thin ewes, during the first 90 days of pregnancy helps promote embryo survival. The embryo implants itself in the uterus approximately 3 weeks after fertilization, and placental development occurs shortly afterwards. The placenta connects the developing fetus (lamb) to its mother and provides nourishment for the fetus to grow, while also eliminating waste products. Good nutrition enables the placenta to develop to full size during this period, thereby providing the fetus with optimal amounts of nutrients. Poor placental development can impact lamb birth weights and can ultimately affect the future reproductive potential of a lamb. Lamb birth weight is one of the most significant predictors of lamb survival, as smaller lambs are less likely to survive birth as compared to lambs with average birth weights. In fact, approximately 70% of lamb mortalities that occur before weaning occur during the first 48 hours after birth. Therefore, producers should balance rations to meet the nutritional requirements of their sheep.
Rations should provide adequate energy, protein, vitamins, and minerals. Typically, a good-quality pasture and a well-formulated mineral mix specifically designed for sheep provide sufficient nutrients to support early pregnancy. However, pay close attention to pasture mixtures during the first 45 days of gestation. Legumes, and red clover in particular, produce phytoestrogens. These estrogenic compounds can impact reproduction by reducing ovulation and conception rates. Fertility generally returns to normal within four to six weeks after removing the sheep from pastures containing high percentages of legumes. Small percentages of legumes typically have little impact on reproduction.
Nutrient requirements for pregnant ewes remain relatively constant during the first two-thirds of pregnancy. However, nutrient requirements increase significantly during the last third of pregnancy. Seventy percent of fetal growth occurs during this time frame, and this rapid growth requires that ewes consume higher levels of nutrients. According to Nutrient Requirements of Sheep, a ewe carrying a single lamb requires approximately 34% more energy in her diet. In comparison, a ewe carrying twins requires approximately 61% more energy in her diet during the last third of pregnancy. While protein requirements do not increase significantly, calcium requirements double, and the requirements for selenium and vitamin E also increase.
To meet increased energy needs, producers typically need to supplement the diet with grain. Producers may also need to supplement the diet with calcium or protein, depending on forage quality and the type of forage. Rations that do not provide enough energy can cause ewes to mobilize body fat, which can result in the disease pregnancy toxemia. Poor nutrition can also result in small and weak lambs, higher lamb mortality, and decreased colostrum quality and quantity, as well as decreased overall milk production, because mammary tissue develops during this stage.
Taking the time now to analyze forages and feeds, and then balancing rations, can be well worth the effort and expense. As pregnancy continues, be sure to assess the body condition scores of ewes. Ensure they receive adequate nutrition to support a body condition score of 3, or provide additional nutrients in the diet to improve body condition scores. The ultimate goal is for ewes to consume a diet that promotes embryo survival, results in a healthy set of twins, and ensures a plentiful supply of high-quality colostrum and milk.
