Feeding Fat to Pregnant Ewes

Dr. Ale Relling, Assistant Professor, Department of Animal Sciences, The Ohio State University

Should we feed fats to pregnant ewes?

This question is being posed in order to summarize what was presented on December 1, 2018 at the Buckeye Shepherd’s Symposium on feeding fats to pregnant ewes. Before I enter into the details of the results and economic implications, I would like to clarify two things. First, we must consider ruminant physiology and applicability, noting that the sources of fats/lipids used are commercially available products. Second, the goal of all studies were not to improve or change ewe physiology, but to evaluate the effect of feeding fats during gestation and the impact that they had on the offspring. As an important note, there were no differences in ewe body weight or body condition score at the start of the experiment, lambing, or weaning.

In the first experiment that we conducted (Coleman et al., 2018 a and b; Carranza Martin et al., 2018), different sources of fat fed during the last 50 days of gestation were compared. The fat sources were calcium (Ca) salts of palm oil, containing a high concentration of saturated and monounsaturated fatty acids (lipids) vs. a Ca salt that contained very long chain, polyunsaturated fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The ewes were fed to provide the nutrient requirements for a pregnant ewe, and the aforementioned fat sources were added at a 0.39% of the diet on a dry matter (DM) basis. Upon lambing, all ewes and lambs were placed onto a common pasture. Lambs were weaned at 60 days of age and remained on pasture for an additional 30 days. Lambs were put in a confinement barn and fed a diet containing 61% ground corn, 11% soybean meal, 24% soyhulls, and the remainder consisting of minerals and vitamins. Lambs were fed this diet for 6 weeks. At the end of the experiment, lambs born from ewes supplemented with very long chain polyunsaturated fatty acids weighed 4.6% more (4.5 lbs.) than lambs born from the ewes supplemented with saturated and monounsaturated fats. Despite the difference in body weight, there was no difference in feed intake.

In a second experiment (Hamer et al., 2018; Nickles et al., 2018), we wanted to confirm that the difference in body weight was due to a beneficial effect of polyunsaturated fatty acids (EPA and DHA) and not due to a negative effect of the saturated/monounsaturated fatty acids. Therefore, we compared the addition of 0%, 1%, or 2% Ca salts that contained very long chain polyunsaturated fatty acids during the last trimester of gestation. The management of the ewes and lambs were similar between treatments, but rather than going onto pasture they remained in confinement and were directly fed a finishing diet. The finishing diet was similar to the previous experiment, with the exception that lambs were fed this diet for 8 weeks. We saw a linear increase in body weight in lambs supplemented with the polyunsaturated fats. Lambs born from ewes supplemented at 2% with polyunsaturated fatty acids weighed 6.9% more (7.5 lbs.) than lambs born from ewes without supplemental fatty acids. Feed intake showed a quadratic effect (U shape). Lambs born from ewes supplemented with 0% or 2% fat had similar feed intakes, but lambs born from ewes supplemented with 1% fat showed a decrease in feed intake of 12% (0.31 lb./day).

Now, the question you might have is, “what is the net profit of feeding a product like this?” In an attempt to address this question, we will take examples from experiment 1 and experiment 2. The product that we used cost $2.54/lb. Therefore, the total cost of supplementing fat in experiment 1 (considering a $0 cost for saturated/monounsaturated fat) was $1.96/ewe (0.25 oz. of product for 50 days). In Experiment 2, when we compare 0% vs. 2% fat (to simplify the equations, because both groups have similar feed intake), the cost was $9.80/ewe. However, profit will ultimately depend on the number of lambs per ewe and the selling price of the lambs. Some examples are in Table 1 for experiment 1 and Table 2 for experiment 2.

Table 1: Total and net profit of supplementing 0.39 % of Ca salts – polyunsaturated fatty acids

Table 2: Total and net profit of supplementing 2% of Ca salts – polyunsaturated fatty acids

In conclusion, supplementation of very long chain polyunsaturated fatty acids to pregnant ewes improves the performance of lambs. With diets containing 2% of the product, the net profit is always positive when the number of lambs per ewes is more than 1.2, even with lamb prices at $1.10/lb. live weight.