Importance of Dietary Arginine in Swine Production
Arginine plays multiple roles in animal metabolism by serving as a substrate for protein synthesis, an intermediate in the hepatic urea cycle, and a precursor for the synthesis of various metabolic molecules, including nitric oxide (NO) and polyamines. It is the production of these molecules that has been of particular interest to Dr. Kim because of their roles in fetal and placental development. Nitric oxide has been shown to play a crucial role in enhancing blood flow during ovine pregnancy (McCrabb et al., 1996; Sladek et al., 1997; Fan et al., 1998; Gardner et al., 2001), thereby increasing the delivery of nutrients to the fetus, and polyamines are important for both embryogenesis and placental growth. Additionally, both NO and polyamines play key roles in angiogenesis, which is a critical event during placental growth and fetal development (Wu et al., 2004). Dr. Kim’s discovery that there is an unusual abundance of arginine (4–6 mmol/L) in porcine allantoic fluid during early gestation has led to research to improve the reproductive performance of pigs.
In a study utilizing 52 pregnant gilts, Dr. Kim’s research team demonstrated that dietary supplementation with an additional 1% arginine between days 30 and 114 of gestation improved the number of pigs born alive per litter.
In a follow-up study utilizing 38 first-parity sows, Dr. Kim’s group examined the impact of dietary arginine supplementation during gestation and lactation on lactation performance and subsequent piglet growth. The sows were fed either an isonitrogenous control diet or a diet supplemented with 1% arginine from 30 days of gestation until farrowing. After farrowing, the sows were then fed either a isonitrogenous control lactation diet or a lactation diet supplemented with 1% Arginine in a 2×2 factorial design. Within 24 hours of farrowing, litter sizes were normalized by cross-fostering. On day 7 of lactation, plasma concentrations of arginine and insulin in sows, as well as concentrations of most amino acids in their milk, were greater (P < 0.05) among the Arginine-supplemented animals. The body weight gain of piglets from sows fed the arginine-supplemented diet during lactation was also greater (approximately 20g/day more, P < 0.05) than that of piglets from the sows fed the isonitrogenous control diet. Collectively, results from this study indicate the beneficial effects of dietary arginine supplementation in improving the lactation performance of first-parity sows.
Protein Digestibility in Neonates
In addition to his recent work regarding dietary arginine supplementation, Dr. Kim’s research group has also examined the digestibility of amino acids in colostrum. Although the functions of colostrum on the health and growth of neonates have been extensively studied, the bioavailability and digestibility of nutrients in this special food has not been studied in neonatal pigs. In a study reported in Livestock Science, Dr. Kim’s group determined the digestibility of the proteins in colostrum. In this study, colostrum was collected from 400 sows, pooled, and frozen prior to use. A total of 12 1-day-old pigs were utilized in a 3-day total collection study. Despite the virtually 100% digestibility of the amino acids in colostrum, the researchers believe that arginine from colostrum may not be sufficient to maximize the performance of neonatal pigs. Dr. Kim has previously shown that dietary supplementation of 0.4% arginine to a basal milk formula containing 0.67% arginine improved the growth and general health of young piglets compared to those fed the basal milk formula alone (Kim and Wu, 2004).
Evaluation of Yeast Culture in Sow Diet to Improve Piglet Performance
While a large part of Dr. Kim’s research involves protein and amino acid nutrition, he also has a great deal of interest in evaluating other feed additives for use in swine production. Recently he has reported a study that examined the use of dietary inclusion of a yeast culture fed to sows on subsequent piglet performance in the Asian-Australasian Journal of Animal Science. Limited nutrient intake during lactation coupled with increased demand for milk production to support a large litter often leaves sows with severe catabolic condition and may reduce sow longevity. Alternatively, restricted milk production, which would be less taxing on the sow, will not satisfy the nutrient demands of the piglets. Proper nutritional management to to minimize the negative energy balance of the sow while maximizing milk output to support the growth of her litter is an important issue in swine production. Dietary supplementation of yeast culture is frequently used to improve milk production of dairy cows; however, the effects of yeast culture supplementation in sow diets has not been thoroughly investigated. To provide industry relevant data on this question, Dr. Kim’s group utilized 335 sows at a commercial facility. The gestation and lactation diets and feeding regimes used at the commercial facility were not altered with the exception of the top-dressing of a yeast culture product (Diamond V Mills, Cedar Rapids, Ia.) on the diet fed to the treated sows. This dietary addition of yeast culture improved (P < 0.05) the growth of the piglets without affecting the feed intake of the sows or their time to return to estrus. Although further studies as to the mechanisms responsible for this improvement are needed, several potential factors could contribute to the heavier piglets at weaning with yeast-culture supplementation. They include but are not limited to (1) increased sow milk production, (2) improved milk quality, (3) increased mobilization of sow body reserves and (4) improved nutrient digestibility.