The vital role arginine plays in gestation
Sunday, February 6, 2011
Research suggests that placental insufficiency is a major factor contributing to suboptimal reproductive performance and low birth weights in piglets and that these amino acids play an important part in improving pregnancy outcomes in pigs
by JANICE MURPHY
In the swine industry, prenatal mortality can run as high as 50 per cent, with the bulk of embryo loss occurring during the first two to three weeks after breeding. Factors generally associated with embryo loss include the stage of pregnancy, health status, sow age, genetics, nutritional status, external environment, intrauterine environment and stress.
When it comes to nutrition, the general guideline is to provide a good, level plane of nutrition before, during and after breeding. In gilts particularly, pre-mating nutritional status appears to have a greater impact on the number of embryos and survival than the post-mating diet, so "flushing" gilts with an extra kilogram of feed during the estrus cycle prior to mating is common. This approach may work for sows as well, although most post-weaned sows will voluntarily restrict their own feed intake. However, various studies have indicated that high feed intake during the first 30 days following breeding may also have a negative impact on embryo survival rates. This has led to the practice of maintaining sows and gilts on a level feed plane at or slightly above maintenance following breeding.
Research suggests that placental insufficiency is a major factor contributing to suboptimal reproductive performance and low birth weights in piglets. Using nutrition to enhance placental growth and function may offer an effective solution to improving embryonic and fetal survival and growth.
Researchers in Texas recently discovered an unusual abundance of the arginine family of amino acids in porcine allantoic fluid, a nutrient reservoir, during early gestation when placental growth is occurring most rapidly. Arginine is metabolized to ornithine, proline and nitric oxide, compounds which are involved in a wide range of physiological functions, including protein synthesis and cell proliferation in the placenta.
Intrauterine growth retardation in pig production.
Of all the livestock species, pigs exhibit the most severe naturally occurring intrauterine growth retardation (IUGR). Up until day 35 of gestation, porcine embryos of similar weight are uniformly distributed within the uterine horns.
The turning point appears to occur at or beyond day 35, when uterine capacity becomes a limiting factor for fetal growth. Blood flow and the supply of nutrients to conceptuses around this time vary greatly along the length of the uterus due to differences in vasculature. Research is suggesting that fetal growth is compromised by the widespread practice of restricted feeding programs in the swine industry during gestation in an attempt to prevent excessive weight gains.
Fetal growth retardation has long-lasting negative effects on life outside the uterus, with implications on pre-weaning survival, growth rate, feed efficiency, overall health, body composition (protein, fat, and minerals), meat quality and reproductive performance. Most IUGR piglets die before weaning, while the survivors suffer permanent growth retardation.
In a breeding study carried out between 2003 and 2009, researchers in Texas reported that IUGR piglets represented 76 per cent of preweaning deaths in pigs. It is common practice on farms for IUGR piglets to be culled, with no nutritional support to increase their growth or survival during suckling and post-weaning periods. Since high prenatal mortality and IUGR remain significant issues, strategies that can increase embryonic and fetal growth and development are important for optimizing the efficiency of pork production.
Improvement of pregnancy outcome by functional amino acids.
As previously mentioned, the naturally occurring inability of the sow's placenta to supply sufficient nutrients to its fetuses is compounded by the widespread practice of restricted feeding programs.
Although this feeding strategy can prevent excessive weight gain during gestation, as well as address farrowing difficulties and appetite reduction during lactation, it creates a situation where gilts and sows cannot receive sufficient amounts of dietary amino acids to support optimal embryonic and fetal survival and growth during early to late gestation. Of particular interest, in this case, is the relationship between restricted feeding programs and the resulting inadequate provision of arginine to fetuses.
Arginine is broken down extensively by an enzyme called arginase in the small intestine, allowing only 60 per cent of dietary arginine to make it through to the circulatory system of pregnant gilts. It stands to reason that increasing dietary levels of arginine above and beyond that provided by a typical ration may be an effective way to increase circulating levels and improve pregnancy outcomes in pigs.
Researchers in Texas point to the results of several experiments to support this hypothesis. First, supplementing diets with one per cent arginine between days 30 and 114 of gestation increased the number of live-born piglets by two and litter birth-weight by 24 per cent. Second, supplementing diets with one per cent arginine to gilts or sows between days 14 and 28 of gestation increased the number of live-born piglets by approximately one at farrowing. Third, supplementation with one per cent arginine between days 14 and 28 of gestation increased the number of fetuses on day 70 by three per litter.
Arginine may also co-operate with other functional amino acids to improve reproductive performance of pigs. Glutamine uptake by the uterus of gestating gilts is the highest among all of the amino acids and it is also abundant in both uterine and fetal fluids.
Armed with this information, researchers developed an arginine-glutamine mixture for feeding to gestating sows. They discovered that adding 0.6 per cent glutamine and 0.4 per cent arginine to a typical diet prevented a decrease in glutamine concentrations in gilt plasma (see Table 2) that occurred in response to dietary supplementation with only arginine between days 30 and 114 of gestation. This modified diet significantly reduced concentrations of ammonia and urea in maternal plasma, an indicator of improved utilization of dietary protein and amino acids. It also decreased variation in birth weights as well as the proportion of piglets with birth weights of 0.6 to 1.29 kilograms. The results showed that adding arginine and glutamine to the diet increased the number of live-born piglets by 1.4 per litter, litter birth weight and the proportion of piglets with birth weights of 1.3 to 1.49 kilograms. These results clearly point to an important role for functional amino acids in improving pregnancy outcomes in pigs.
In conclusion, placental insufficiency is a major factor contributing to IUGR in pigs. The underlying mechanisms are undoubtedly complex, but may include inadequate or disproportionate amounts of functional amino acids available during development in the uterus.
Research on the biochemical mechanisms responsible for effects of amino acids has revealed little to date and has historically been studied by standard low-output methods. However, recent advances in the development of high-output approaches (genomics, epigenomics, proteomics and metabolomics) are transforming nutrition research.
These powerful research tools will accelerate our understanding of how amino acids regulate gene expression and biosynthetic pathways to affect embryonic and fetal survival as well as placental and fetal growth. These new techniques should advance basic research on amino acid biochemistry and physiology, and ultimately translate into practical feeding practices that will improve reproductive performance in the swine industry. BP
Source: G. Wu, F. W. Bazer, R. C. Burghardt, G. A. Johnson, S. W. Kim, X. L. Li, M. C. Satterfield and T. E. Spencer. 2010. Impacts of amino acid nutrition on pregnancy outcome in pigs: mechanisms and implications for swine production. J. Anim. Sci. Apr;88 (13 Suppl):E195-204.
Janice Murphy is a former swine nutritionist with the Ontario Ministry of Agriculture, Food and Rural Affairs who now lives and works in Prince Edward Island.