The effect of dietary energy concentration and total lysine/digestible energy ratio on the growth performance of weaned pigs

Amino acids should be defined in relation to dietary energy concentration in diets for young pigs. However, the literature contains diverse estimates of the optimum ly sine: digestible energy (DE) ratio for weanling pigs performing at levels commonly observed in commercial practice. Further, there is a poor understanding of the reponse of the weanling pig to dietary energy concentration. A growth experiment was conducted to define the optimum total lysine:DE ratio for pigs from 4 to 8 wk of age. Dietary treatments were arranged as a 2 x 5 factorial: low (LDE, 3.4 Mcal kg(-1)) or high DE (HDE, 3.6 Mcal kg(-1)) and the following total lysine:DE ratios: 3.7, 4.0, 4.3, 4.6, or 4.9 g Mcal(-1)). The experiment ran for 28 d, beginning 7 d post-weaning, using four pigs per pen and six pens per diet for a total of 240 pigs (27 +/- 2 d; 7.5 +/- 1.1 kg). No DE x lysine:DE ratio interactions were detected for any performance parameter (P > 0.05). The average daily feed intake (ADFI) was 4% greater with pigs on LDE than HDE diets (DE, P < 0.05), but was not affected by lysine:DE ratio (P > 0.05). Conversely, DE did not affect average daily gain (ADG) (P > 0.05), but increased quadratically (day 0 to 14; P < 0.05) and (day 0 to 28; P < 0.10) with increasing lysine:DE ratio. Feed efficiency increased linearly with increasing lysine:DE ratio (P < 0.05) and was 4% greater with the HDE than LDE diets (P < 0.05). The optimum total lysine:DE ratio for ADG was determined to be 4.46 and 4.27 g Mcal(-1) for pigs between 7.5 to 13 kg and 7.5 to 22.5 kg BW, respectively.