By Melanie Barkley
Producers should strive to meet nutritional requirements for their sheep regardless of the time of year. This becomes even more important during breeding season and throughout pregnancy. Nutrition impacts body condition scores, body condition scores impact ovulation rates, and nutrition also plays an important role in embryonic survival. Throughout pregnancy body condition scores and nutrition impact health and vigor of newborn lambs and colostrum quality and quantity.
Sheep body condition is scored 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 slighter higher. The higher score takes into account the fact that most ewes lose body condition during lactation. However, a slighter lower score at the start of breeding season and an increasing plane of nutrition will flush ewes to encourage a higher ovulation rate.
In order to improve body condition scores of thin ewes, a good goal would be to increase body weight by 10% over a 100-day period. A good balance might mean that producers strive to have their ewe flock scoring slightly below a 3 at the start of 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 a 3.
In addition to body condition scores, producers should manage body weight on 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. In order 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 on pasture. This rate of gain results in ewe lambs weighing less than recommended for breeding. Therefore, producers should calculate weight gain required and adjust rations to accommodate a faster rate of gain. Young ewes also need to continue their weight gain throughout pregnancy to account for their continued growth as well as the growth of a 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 about 3 weeks after fertilization and placental development occurs shortly after that. The placenta connects the developing fetus (lamb) to its mother and provides nourishment for the fetus to grow plus eliminates waste products. Good nutrition allows the placenta to develop to full size during this period, thus providing optimal amounts of nutrients to the fetus. Poor placental development can impact lamb birth weights and can ultimately impact the future reproductive potential of a lamb. Lamb birth weight is one of the greatest 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 prior to weaning occur during the first 48 hours after birth. Therefore, rations should be balanced to meet nutritional requirements.
Rations should provide adequate energy, protein, vitamins, and minerals. Typically, good quality pasture and a good quality mineral mix provide enough 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 generally do not have much impact on reproduction.
Nutrient requirements for pregnant ewes remain about the same during the first two-thirds of pregnancy. However, nutrient requirements increase significantly the last third of pregnancy. Seventy percent of fetal growth occurs during this timeframe 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, while a ewe carrying twins requires approximately 61% more energy during the last third of pregnancy. While protein requirements do not increase significantly, calcium requirements double, and selenium and vitamin E requirements increase.
In order to meet increased energy needs, you typically need to add some grain to the ration. You may also need to supplement the ration with calcium or protein, depending on forage quality and 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 death loss, and decreased colostrum quality and quantity as well as decreased overall milk production because mammary tissue develops during this stage.
Taking time now to analyze forages and feeds and then balance rations can be well worth the time and money. As pregnancy continues, be sure to assess body condition scores of ewes. Make sure they receive adequate nutrition to support a body condition score of 3 or provide additional nutrients in the ration to improve body condition scores. The ultimate goal is for ewes to consume a ration that will promote embryo survival, result in a healthy set of twins, and ensure plenty of high quality colostrum and milk to consume.
Source : psu.edu