In Addition To Providing Energy, Supplemental Oil May Have Positive Effects on Reproduction in Heifers
1Sushil Kumar, 2Sajjan Sihag, 3Zile Singh Sihag and 4Hardeep Kalkal
1, 2, 3Department of Animal Nutrition, LUVAS, Hisar-125004
4Department of Veterinary Parasitology, International Institute of Veterinary Education and Research, Rohtak, Haryana, India- 124001 and corresponding author
Introduction
Heifers must attain 30 to 40% of their mature body weight to reach puberty and 65% of their mature body weight to conceive for optimizing production. Age at puberty is an important production trait; and hormones, nutrition and genotype play key roles in attainment of puberty. For successful dairy farming, a complete package of replacement heifer rearing is imperative to exploit the performance potential at minimum expense. The input in dairy industry in term of feed cost represents around 80% of the total input costs for heifer production. Therefore, adequate nutrient supply is paramount to the development of heifers. Generally, cereals, oil cakes, oil, mineral and salt supplements are used with forages to meet the nutritional needs of animals. Cereal grains and oils are the chief energy supplements. Dietary energy intake influences reproductive performance of animals. However, high levels of grains in the concentrate mixture can adversely affect dry matter intake, rumen fermentation and fiber digestibility in ruminants. For it, the fat supplements are commonly used @ 20 to 30 g/kg dry matter intake without negatively affecting fibre digestibility. In addition to providing energy, supplemental oil may have positive effects on reproduction, particularly the fatscontaining polyunsaturated fatty acids. Formerly, fats were added to the diet of ruminants to increase the energy density and alleviate the negative energy balance during early lactation. However, recent studies have unveiled many beneficial effects of fats, especially the one rich in polyunsaturated fatty acids, other than providing energy. Unsaturated fats have been reported to modify a number of ovarian physiological processes, including follicular growth and function; and the lifespan of induced corpora luteum in cattle. Unsaturated fats are precursors of lipid mediator molecules, such as prostaglandins, prostacyclins, thromboxanes, leukotrienes that carry out many important cellular functions. They are incorporated into phospholipids of cell membranes, which influence structural and functional properties of cells.Some fatty acidsare essential for animals (omega-3 and omega-6 polyunsaturated fats) and because of their role on reproductive processes, it is possible that cattle reproduction will be influenced more by the type of fat consumed than for the total fat intake. In ruminants, a major impediment for delivery of unsaturated fat for absorption is ruminal-bio-hydrogenation. In fact, ruminal bio-hydrogenation of omega-3 and omega-6 polyunsaturated fats is extensive; around 80% of fatty acids from the diet are modified by the ruminal microflora and, therefore, not available for absorption in the small intestine. Still, some unsaturated fat may pass intact through rumen and is absorbed from the small intestine, allowing in this way the improvement of reproductive efficiency directly on the target tissue of the reproductive system of the female or by an indirect effect mediated by the endocrine system.Polyunsaturated fats contain linoleic acid, alpha-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid that may target reproductive tissues and alter reproductive function and fertility in cattle. These fatty acids are usually derived from plants and oil seeds sources such as sunflower, linseed, rapeseed and soybean, and; has been reported to exert a major impact on reproductive performance of dairy animals. Unsaturated fats like soybean oil and linseed oil are found to increase the number and size of medium and large ovarian follicles and prolonged lifespan of consequent corpus luteum in cycling heifer. Omega-6 and omega-3 rich oil also increase the serum concentrations of insulin, growth hormone and ovarian follicular IGF-I concentrations, which may positively affect reproduction efficiency of dairy animals. Many other studies also confirm the positive effects of unsaturated fats on reproductive aspects such as the establishment of puberty, maternal recognition of pregnancy, follicle development, oocytes quality and modification in the mechanism of synthesis and secretion of hormones involved in reproductive processes. Therefore, it can be concluded that despite limitations in delivery of specific amounts of polyunsaturated fats for absorption, supplementation of oils containing polyunsaturated fatty acids in the ration of heifers is capable of influencing their reproductive performance.
