Effects of the standardized ileal digestible lysine to metabolizable energy ratio on performance and carcass characteristics of growing-finishing pigs

Two important objectives in pig production are to maximum growth rate and improve the efficiency of nutrient utilization [1]. Dietary lysine is a key factor which influences the achievement of these objectives because it is the first limiting amino acid in diets fed to swine [2]. Dietary energy influences feed intake in growing-finishing pigs fed ad libitum [3,4], so that a pig's amino acid intake may be altered as the energy content of the diet changes. Therefore, it is necessary to maintain an optimum lysine to energy ratio when the amino acid or energy content of the diet increases [1,3].Previous studies have been conducted using variable ratios of lysine to energy [1]. Cho et al. [5] observed that the best lysine to digestible energy (DE) ratio for maximum amino acid digestibility of the pig is 2.4 g total lysine/Mcal DE for barrows (Landrace × Yorshire × Duroc; 64 kg). Chang et al. [6] showed that the optimal lysine to DE ratios were 3.2 and 3.8 g total lysine/Mcal DE for barrows and gilts (Landrace × Yorshire × Duroc; 16 to 57 kg), respectively. Bikker et al. [7] suggested that 2.5 g apparent ileal lysine/Mcal DE was required to optimize performance for lean gilts (20 to 45 kg). Factors which are responsible for the variation include environment and advance in the genetics of modern pigs [8,9]. Previous recommendation [2] is no longer fulfilling the desperate need of animal industry and production in China. Therefore, it is necessary for us to further research the lysine and energy requirement of growing-finishing pigs (Duroc × Landrace × Large White) under commercial pig farms condition in Hebei province, thereby contributing to the solid construction of Chinese feeding criterion.Ileal digestibility coefficients for amino acids can be expressed as apparent, standardized or true. However, apparent ileal digestibility values are not always additive in a mixed diet [10]. In addition, it is difficult to measure specific endogenous amino acid losses and as a resul