Effect Of Dietary Lysine To Protein Ratio On Performance And The Efficiency Of Nitrogen Utilization In Swine

Three feeding trials and two metabolic trials were conducted to investigate the effects of lysine to protein ratio in practical swine diets on performance and the efficiency of nitrogen utilization in sow, piglet and growing-finishing pig.In trial 1 and 2, 30 later pregnant sows and 60 lactating sows were selected and allotted to five treatments, respectively, based on the parities and body weight. In pregnant sow trial, five lysine to protein rations was 3.5,4.0,4.5, 5.0 and 5.5 g/100 g, respectively. Each treatment had six replicates. The results showed that the body weight and the back-fat thickness of sows were increasing linearly with lysine to protein ratios increased from 3.5 to 4.5 (P < 0.05); with the ratios of lysine to protein increased from 3.5 to 5.5, the serum urea nitrogen significantly decreased linearly or quadraticly (P < 0.05), but serum free amino acid increased linearly or quadratic (P < 0.01); the optimum lysine to protein ration was 4.0-4.5 g/100 g for later pregnant sows. In lactating sow trial, five treatments of lysine to protein rations was 4.8, 5.3, 5.8, 6.3 and 6.8 g /100 g, respectively. Each treatment had twelve replicates (each sow as a replicate). The results showed that the body weight loss and back-fat thickness loss of lactating sows decreased quadraticly with the increasing of lysine to protein ratio (P < 0.05). The body weight loss occurred earlier than that of back-fat loss. The 20th day's milk yield and litter body weigh gain increased linearly (P < 0.01) or quadraticly (P < 0.05) with the increased of lysine to protein ratios, but the 21th day milk compositions had no significant change (P > 0.05); with the ratios of lysine to protein increased, the serum urea nitrogen on 14th and 21th day decreased linearly or quadraticly (P < 0.01) while as the serum free amino acid has a linearly and quadraticly (P < 0.05), which showed to improve the efficiency of nitrogen utilization and decrease the nitrogen excretion.In trial 3, 90 piglets with 7.8 + 1.0 kg initial body weight were selected to study different lysine to protein ratios on performance and serum parameters of weaned pigs. Piglets were equally allotted to one of five treatments according to initial body weight, litters and sex. The protein concentration in the basal diets was 20% and the ratios used were 5.1, 5.6, 6.1, 6.6 and 7.1g/100 g CP, respectively. The results showed that feed efficiency was significantly improved (P < 0.05) by the increasing of dietary lysine to crude protein ratio. Serum urea nitrogen concentration decreased linearly (P < 0.01) and serum free lysine content increased linearly (P < 0.01) as the lysine to protein ratio in diets increased from 5.1 to 7.1 g/100g. The best of the ratio was 6.1 g lysine/100 g crude protein for piglets from 8 to 20 kg.In trial 4 and 5, two. metabolic trials were arranged to study the effect of the lysine to protein ratios on efficiency of nitrogen utilization in growing-finishing pigs. Five barrows with initial body weights of 26.0+2.4 kg and 60.5+2.9 kg. were use in each of the two trials, respectively. The pigs were allotted to five dietary treatments according to 5x5 Latin square design. In trial 4, the ratios of lysine to protein were 4.7, 5.2, 5.7, 6.2 and 6.7 and the ratios were 4.5, 5.0, 5.5, 6.0 and 6.5 g lysine/100 g CP in trial 5, respectively. The results showed that nitrogen retention in growing pigs decreased linearly (P < 0.01) with the dietary lysine to protein ratios increased inboth of the two trials. The maximum nitrogen retention was observed when the ratio of lysine to protein was 5.2 g/100 g and 5.0 g/100 g in trial 4 and 5. respectively. In trial 4, apparent biological value and gross nitrogen efficiency increased linearly (P < 0.01 and P < 0.05, respectively) with the lysine to protein ratios increased from 5.2 to 6.7 g lysine/100 g CP. In trial 5, the ratios of lysine to protein could significantly affect the urinary nitrogen concentration (P < 0.05); the ratio of 5.0 could decrease the urinary nitrogen concentration and increase...