Determining an optimum Lysine:calorie ratio for barrows and gilts in a commercial finishing facility

¹ Food Animal Health and Management Center, Kansas State University, Manhattan, 66506-0201
² Department of Animal Sciences and Industry, Kansas State University, Manhattan, 66506-0201

^* To whom correspondence should be addressed. E-mail: Goodband{at}ksu.edu.

	Abstract

Our objective was to determine an optimum Lys:calorie ratio (g total dietary Lys/Mcal ME) for 35- to 120-kg barrows and gilts (Pig Improvement Company, L337 x C22) in a commercial finishing environment. Seven (3 barrow, and 4 gilt) trials were conducted using randomized complete block designs (42 pens per trial, a total of 7,801 pigs). Six treatments with increasing Lys:calorie ratio were used in each study. Diets were corn-soybean meal-based with 6% choice white grease. Lysine:calorie ratios were attained by adjusting the amount of corn and soybean meal. No crystalline Lys was used. In Barrow Trial 1 (43 to 70 kg), increasing Lys:calorie ratio (2.21, 2.55, 2.89, 3.23, 3.57, 3.91) increased (quadratic, P < 0.01) ADG, G:F, income over feed costs (IOMFC), feed cost per kg of gain, and decreased (linear, P < 0.01) backfat. In Barrow Trial 2 (69 to 93 kg), increasing Lys:calorie ratio (1.53, 1.78, 2.03, 2.28, 2.53, 2.78) improved (linear, P < 0.01) ADG, G:F, IOMFC, and decreased (quadratic, P < 0.01) backfat. In Barrow Trial 3 (102 to 120 kg), increasing Lys:calorie ratio (1.40, 1.60, 1.80, 2.00, 2.20, 2.40) increased (linear, P < 0.03) ADG, G:F, and numerically improved (linear, P = 0.12) IOMFC. In Gilt Trials 1 (35 to 60 kg), 2 (60 to 85 kg), and 3 (78 to 103 kg) increasing Lys:calorie ratio (2.55, 2.89, 3.23, 3.57, 3.91, 4.25; 1.96, 2.24, 2.52, 2.80, 3.08, 3.36; and 1.53, 1.78, 2.03, 2.28, 2.53, 2.78, respectively) improved (quadratic, P < 0.04) ADG, G:F, IOMFC, feed cost per kg of gain and reduced (linear, P < 0.01) backfat. In Gilt Trial 4 (100 to 120 kg), increasing Lys:calorie ratio (1.40, 1.60, 1.80, 2.00, 2.20, 2.40) improved (linear, P < 0.02) ADG, G:F, LM depth, IOMFC and (quadratic, P < 0.06) feed cost per kg of gain. These studies suggest feed cost per kg of gain decreases, and reductions in biological performance and IOMFC are rather modest when feeding marginal Lys deficient diets early (35 to 70 kg) in the grower-finishing period, as compared to the more severe penalties in growth and economic performance of feeding marginally deficient diets in late finishing (70 kg to slaughter). The equations (Lys:calorie ratio = - 0.0133 x BW, kg + 3.6944 and = - 0.0164 x BW, kg + 4.004, for barrows and gilts, respectively) best describe our interpretation of the Lys:calorie ratio that met biological requirements and optimized IOMFC on these pigs (PIC, L337 x C22; 35 to 120 kg) in this commercial finishing environment.

Key Words: finishing, lysine, swine