Estimates of the optimum dietary ratio of standardized ileal digestible valine to lysine for eight to twenty-five kilograms of body weight pigs.

Valine is among the limiting AA in low protein diets for pigs, but data are currently lacking for empirical requirement studies. Therefore, 2 growth assays and 1 N-balance trial were conducted to determine the Val requirement of weaned pigs (8 to 25 kg of BW) expressed as the ratio of standardized ileal digestible (SID) Val to Lys. In Exp. 1, 48 pigs (individual housing; equal proportion of castrates and females; initial BW = 8.0 kg) were randomly subdivided into groups receiving 6 dietary treatments. Dietary SID Val:Lys ratio was increased by adding L-Val from 0.56 to 0.84% (planned increments of 0.06%) at an average SID Lys level of 0.99%. Other crystalline AA were supplied to meet optimum SID AA:Lys ratios based on the concept of an ideal protein. All diets were isocaloric (13.6 MJ of ME/kg) and isonitrogenous (17.8% CP). For the 35-d period, ADG and ADFI increased linearly (P < 0.01) and quadratically (P < 0.01) with increasing SID Val:Lys. However, the data were not suitable for estimation of Val requirement. Therefore, in Exp. 2 the dietary basal level of Val was reduced to 0.49% SID Val and 4 increments of 0.04% and 1 increment of 0.08% L-Val were used to give 6 dietary treatments (48 pigs; individual housing; equal proportion of castrates and females; initial BW = 7.9 kg). The SID Lys level averaged 0.99%, and SID Val:Lys ratios ranged from 0.49 to 74%. Other crystalline AA were supplied to meet optimum SID AA:Lys ratios. All diets were isocaloric (13.7 MJ of ME/kg) and isonitrogenous (17.7% CP). For the 34-d period, ADG, ADFI, and G:F increased linearly (P < 0.01), and ADG and G:F quadratically (P < 0.01) as the SID Val:Lys ratio increased. Estimates of optimum SID Val:Lys were 66, 67, and 61% for ADG, ADFI, and G:F, respectively. These estimates were confirmed by minimized concentrations of plasma urea and Lys and by markedly increased concentrations of plasma Val. To verify the estimates of the growth trials, a total of 24 N balances were conducted with 12 pigs using the dietary treatments of Exp. 2 (Exp. 3; equal proportion of males and females; average BW = 14.1 kg; 2 balances per pig). Pigs were restrictively fed 3 times daily. Precollection and collection periods lasted 7 d each and were repeated after rearranging the animals to treatments. Increasing the dietary SID Val:Lys ratio linearly increased N retention (P < 0.04) and quadratically decreased plasma concentrations of urea (P < 0.01). Optimal SID Val:Lys ratios of 65 and 62% were estimated for N retention and N utilization, respectively. We conclude that an optimum SID Val:Lys ratio of 65 to 67% is needed for optimal performance in 8- to 25-kg pigs.

Estimation of the optimum ratio of standardized ileal digestible isoleucine to lysine for eight- to twenty-five-kilogram pigs in diets containing spray-dried blood cells or corn gluten feed as a protein source.

Two growth assays and 1 N balance trial were conducted to determine the standardized ileal digestible (SID) Ile:Lys ratio in 8- to 25-kg pigs using spray-dried blood cells or corn gluten feed as a protein source. In Exp. 1, 48 individually penned pigs (initial BW = 7.7 kg) were used in a 6-point SID Ile titration study (analyzed SID Ile of 0.36, 0.43, 0.50, 0.57, 0.64, and 0.72%) by addition of graded levels of L-Ile. The basal diet contained 1.00% SID Lys, 18.4% CP, and 13.6 MJ of ME/kg. Diets were based on wheat, barley, corn, and 7.5% spray-dried blood cells as a protein source. Dietary SID Leu and Val levels were 1.61 and 1.02%, respectively. For the 35-d period, ADG, ADFI, and G:F increased linearly (P < 0.01) and quadratically (P < 0.04) with increasing SID Ile:Lys. Estimates of optimal SID Ile:Lys ratios were 59% for ADG and ADFI. In Exp. 2, 24 N balances were conducted using the Exp. 1 diets (12 pigs; individually penned; average BW = 11.5 kg). Pigs were fed 3 times daily with an amount equal to 1.0 MJ of ME/kg of BW(0.75). Preparation and collection periods (7 d each) were repeated after rearranging the animals to treatments. Increasing the dietary SID Ile:Lys ratio increased N retention linearly (P < 0.01), and N utilization linearly (P < 0.01) and quadratically (P < 0.01). An optimal SID Ile:Lys ratio of 54% was estimated for N retention. In Exp. 3, 48 individually penned pigs (initial BW = 8.0 kg) were fed grain-based diets in a 6-point SID Ile titration (analyzed SID Ile of 0.35, 0.41, 0.49, 0.56, 0.62, and 0.69%). Dietary SID Ile was increased by graded addition of L-Ile. The basal diet contained 0.97% SID Lys, 16.8% CP, and 13.6 MJ of ME/kg. In contrast to Exp. 1 and 2, spray-dried blood cells were excluded and corn gluten feed was used as a protein source. Dietary SID Leu and Val were set to 1.05 and 0.66%. For the 42-d period, ADG, ADFI, and G:F increased linearly (P < 0.01) and quadratically (P < 0.01) with increasing SID Ile:Lys. Estimated optimal SID Ile:Lys ratios were 54, 54, and 49 for ADG, ADFI, and G:F, respectively. These experiments suggest that the optimal SID Ile:Lys ratio depends on diet composition. In Exp. 1, AA imbalances because of increased Leu contents may have led to increased Ile nutritional needs. For ADG and ADFI, an optimum SID Ile:Lys ratio of 54% was estimated for 8- to 25-kg pigs in diets without Leu excess.