Effects of increasing dietary energy level using carbohydrate or fat supplementation on ovarian activity and some blood parameters in Ghezel ewes

Introduction: Excellent reproductive performance is paramount to profitable farm animal production systems. This is particularly true in strict seasonal reproductive systems where animals are expected to establish and maintain pregnancy within a short period of time. Low reproductive performance in seasonal breeders such as sheep and goat was considered as a main economic problem in modern and nomadic production systems. There are numerous research reports on the impact of nutrition on follicular population, folliculogenesis, and ovulation rate in sheep. Feeding is a low-cost system for managing reproduction and ovulation rates in arid and semi-arid regions (Martin et al. 2004). Animal energy balance and its secondary effect on metabolism through its influence on nutrient concentrations, hormones and various growth factors such as calcium, insulin, growth hormone and insulin-like growth factor may be the most important mechanism to justify the effect of energy on processes Reproduction affected the hypothalamic-pituitary-ovarian axis. Dietary energy in pre-conception period is an influential factor in reproductive activities. Also, there are reports about the positive effects of supplementing diets with polyunsaturated essential fatty acids on reproductive performance in farm animals. Fish oil contains EPA and DHA as omega-3 fatty acids and plays a major role in the production of eicosanoids. On the other hand, plant oils rich in omega-6 fatty acids such as linoleic acid have been reported to improve immune status of animals. The positive effects of fat and energy supplementation on the improvements of reproduction in dairy cows are well documented, but the specific effects of omega polyunsaturated fatty acids (n-3 and n-6) on reproductive success in small ruminants have not been examined in detail. While the link between n-3 fatty acids and reproductive markers such as (PGF2α) are well established, evidences for direct effects of high n-3 fatty acids supplementation on measurable reproductive outcomes in ruminants is limited. There is little information regarding the effect of dietary energy level and energy source on reproductive activity in Iranian fat-tailed lambs.This study was carried out to determine the effects of increasing dietary energy level by carbohydrate or fat supplementation using rumen-protected calcium salts of fish oil as omega-3 fatty acid sources or soybean oil as omega-6 fatty acids on ovarian activity and some blood parameters in Ghezel ewes.
Materials and methods: Twelve Ghezel ewes were assigned into four groups with three animals based on a  completely randomized design. Diets were formulated according to small ruminant’s nutrient requirement using Small ruminant nutrition system (SRNS, Texas A&M University, version 1.11.7154.28131). The control group received maintenance energy requirements. While the second experimental groups received a diet with  20% extra energy supplied by barley grain. Calcium salt of fatty acids rich in Omega-3 fatty acids (eicosapentaenoic and docosahexaenoic acid) and Omega-6 (linoleic acid) were partly replaced with barley grain in third and fourth experimental groups, respectively. The estrous cycle of the ewes was synchronized with two consecutive injections of prostaglandin. Ultrasound examination of the ovaries started after second PG injection and continued for three estrous cycles. Through the first cycle, all of the animals received the control diet. Experimental diets were fed through the second and third estrous cycles. The first cycle for each of the experimental groups was considered as the control for study the effects of different dietary treatments. Blood sampling was done on day 12 of the luteal phase of each experimental cycles, four hours after the morning meal and plasma and serum were analyzed for energy-related parameters such as glucose, triacylglycerol’s, insulin, non-esterified fatty acids, beta-hydroxybutyric acid as well as sex hormones.
Results and discussion: Plasma levels of glucose, triacylglycerol’s, non-esterified fatty acids, beta-hydroxybutyric acid, and serum levels of estrogen and progesterone were affected by energy levels in the diet. However, effects of energy source were also significant in the case of glucose, BHBA and hormones levels. Concentrations of glucose, triacylglycerol, HDL, total protein, albumin, urea VLDL, estrogen, and progesterone (p < 0.05) were affected by the experimental treatments and increased with increasing energy levels. The type of energy source (carbohydrate versus fat) showed a significant difference in concentrations of glucose, cholesterol, VLDL, globulin, estrogen, and progesterone (p < 0.05). The highest plasma glucose concentration was in the barley-receiving group. Increasing the dietary energy level resulted in improvement of various energy indices such as the concentration of non-esterified fatty acids and beta-hydroxybutyrate (p < 0.05). Triacylglycerol and HDL concentrations were not significantly different between ewes consuming different energy sources, but increased with increasing dietary energy levels. Supplementing the diet with protected poly-unsaturated fatty acids has resulted in higher plasma unsaturated fatty acids. In this case, energy levels, energy source, and lipid supplementation type exert significant effects. The use of linoleic acid supplementation in this study increased arachidonic acid concentration (P <0.05). Twenty-carbon unsaturated fatty acids are a direct precursor of a large group of active compounds called eicosanoids, including prostaglandins, thromboxanes, leukotrienes, and lipoxanes. Omega-6 fatty acid supplemented diet increased ovulatory follicle diameter in the third cycle of the experiment compared with control cycle. However, omega-3 supplementation decreased it. On the other hand, the follicular waves counts were not influenced.
Conclusion: Results showed that higher energy content or even the energy source could not significantly affect the various parameters of the estrous cycle such as follicular waves count, length of the estrous cycle, follicular diameter, and the number of ovulation in each cycle (P>0.05). Nevertheless, the change in energy level and the source had been exerted significant effects on plasma fatty acids profile and energy-related metabolites (p < 0.05). This study was performed in the reproductive season with the limited number of animals and it seems  that normal body condition of experimental animals, as well as long term dietary inclusion of high energy supplements, have potentials for affecting  the results. Further examination in reproductive and non-reproductive seasons with more replications and also, investigation of the effects of different energy sources and energy levels on reproductive performance could be suggested.