The effect of the ratio of standardized ileal digestible lysine to metabolizable energy on growth performance, blood metabolites and hormones of lactating sows

Inadequate nutrient intake of sows during lactation can adversely affect their subsequent reproductive performance [1]. Lysine is considered the first-limiting amino acid in typical corn-soybean meal diets fed to lactating sows [2]. For this reason, more research has focused on identifying the lysine requirements of lactating sows than for any other amino acid.When formulating diets for lactating sows, it is common practice to provide lysine at a certain percentage of the diet. However, feed intake decreases as the dietary energy concentration increases [3-5] and as a result, total lysine intake may decline as the energy concentration of the diet increases.Energy restriction has a detrimental effect on sow weight loss throughout lactation, weaning litter weight and weaning-to-estrus interval [6,7]. Thus, an optimum lysine to energy ratio is important to optimize sow reproductive performance. At present, amino acid requirements are often expressed as standardized ileal digestible (SID) values for feed formulation [8]. Therefore, the SID-lysine to ME ratio may be the optimum method of expressing the lysine requirement of lactating sows.Studies of the optimum lysine to energy ratio have mainly focused on young pigs [9-11]. Studies related to lactating sows are relatively scarce. Therefore, the objective of these experiments was to determine the optimum dietary SID-Lys:ME ratio in the diet of lactating sows under local commercial pig farm conditions.The Animal Welfare Committee of China Agricultural University (Beijing, China) approved the animal care protocol used for this experiment.A total of 185 sows (Landrace × Large White), including 36 first parity, 36 second parity, and 113 third-to-ninth parity sows, were used in this experiment. When the sows exhibited estrus, they were mated twice at 12 h intervals using a mature Duroc boar. After mating, the sows were provided 2 kg/day of a commercially prepared gestation diet providing 3.05 Mcal/kg of ME and 0.65% total lys