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Lambing season rolls around every spring, and with it comes night lamb checks, fuzzy little faces bleating for mama, and hopefully, healthy ewes and lambs. But ensuring that those lambs and ewes are healthy at birth starts long before lambing occurs.
Our research group focuses on how the ewe’s diet while she is pregnant affects the growth and development of her lambs. When a ewe is provided excess or restricted nutrition during pregnancy, it affects her ability to support the proper development of her lambs. This is compounded when ewes carry larger litter sizes (2 or more lambs). Development of the lambs during gestation prepares those animals for growth after lambing. Ewes that are over- or under-fed during pregnancy produce lambs that ultimately end up with more fat and less muscle. This is undesirable because there is less meat produced and the animals are less healthy due to increased body fat. Further, lambs from poorly nourished ewes tend to have more connective tissue, resulting in tougher cuts of meat. But there are strategies that producers can easily employ to improve the health and productivity of their flocks.
Transabdominal ultrasound during early pregnancy (around day 30) can be performed with the ewe in the standing position, with little stress to the animal, and in less than 5 minutes per animal by a skilled technician. Ultrasound can provide critical information, such as how many lambs a ewe is carrying and, when appropriate fetal measurements (such as the length from the crown to the rump) are taken, an estimated due date can be calculated. Ewes with larger litter sizes require additional feed, but are also at greater risk for ketosis in late gestation. Identifying the number of offspring early will allow farmers to prevent complications during and after pregnancy.
Once litter size and estimated lambing date are known, flock managers can appropriately feed their ewes according to litter size and stage of gestation. Best practice suggests that ewes should be separated by litter size so that those carrying larger litters can be fed greater quantities of food. This prevents over-feeding ewes that are pregnant with singletons and under-feeding ewes that are pregnant with multiples. Ewes should be fed based on their stage of gestation (early-, mid-, late-), and the number of lambs they are carrying. Importantly, body condition should be monitored throughout gestation to ensure that ewes are carrying sufficient condition into lactation, so that they will be able to support their lambs after parturition. To ensure that the feed provided is appropriate, hay and grain analyses can provide flock managers with the nutrient content of their feedstuffs. Nutritional value can vary widely so it is recommended that each load of feed is analyzed. Feed analysis can be easily completed at several labs at relatively low cost. Determining how much feed to provide is based on nutrient requirements published by the National Research Council (https://www.nap.edu/read/11654/). There are also many online feed calculators available for sheep (https://www.sheepandgoat.com/rationsoftware).
Separating ewes by litter size also allows for closer monitoring of ewes with larger litter sizes that are predisposed to ketosis in late gestation. Ketosis is a common metabolic disorder that occurs during periods of extreme energy demands coupled with an inability to meet those demands. In ewes, this occurs most frequently during late gestation when lamb growth is the greatest. At-risk ewes can be monitored during the last four weeks of gestation for ketosis using a hand-held beta-hydroxybutyrate (BHBA) meter. Concentrations between 0.8 to 1.5 mmol/L are considered subclinical and indicate the need for close monitoring until parturition. Blood concentrations of BHBA greater than 1.6 mmol/L are considered indicative of clinical ketosis and would require veterinary attention.
Beyond understanding the effects of poor maternal nutrition during gestation on lambs, our research helps us understand how human babies who are born to over- or under-nourished mothers may be affected. Sheep are excellent models for human health research, as they have similar numbers of offspring and lambs are approximately the same weight at birth as babies. While there are certainly differences in human and sheep physiology, understanding how a mother’s diet influences her offspring’s growth and metabolism benefits both species. By improving ewe health and nutrition during pregnancy, producers will have better growing lambs with improved carcass characteristics. Improving mom’s health and nutrition during pregnancy will decrease the risk of her baby developing metabolic diseases such as diabetes later in life.
For more information on our research, please visit the Fetal Programming Research Group’s website: https://fprg.research.uconn.edu/.
Article by Sarah Reed, PhD, Associate Professor, Department of Animal Science