Optimizing beef cattle performance using rumen-protected lysine supplementation in diets balanced for predicted amino acid and effective energy requirement
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The objectives of these experiments were to determine the bypass value of rumen-protected lysine and performance responses of beef cattle fed encapsulated lysine. During experiment 1 singe-flow continuous culture fermenters were fed a Lys-deficient control (CON), a Lys-sufficient diet supplemented with rumen-protected soybean meal (RPSBM; AminoPlus, Ag Processing Inc., Omaha, NE), or a Lys-sufficient diet containing a commercially available rumen-protected Lys product (RPLYS; USA Lysine, Kemin Industries Inc., Des Moines, IA). Results from continuous culture showed greater degradation of RPLYS than RPSBM and CON. During Experiment 2, an in vitro dry matter digestibility study showed DM degradation was 23 percent greater for pure USA Lysine than another encapsulated lysine product (AjiPro 2G, Ajinomoto Heartland, Inc., Omaha, NE). The next objective was to test if AjiPro would increase plasma Lys levels in vivo (and therefore indicate its successful ruminal bypass and small intestinal absorption). Experiment 3 involved a 3 x 3 Latin Square study conducted on cannulated crossbred steers fed a combination of rumen-protected soybean meal and two increased levels of the rumen-protected product, where it was fed to meet 100 percent (AJ100) and 150 percent (AJ150) absorbable AA to effective energy (EE) ratio. Plasma Lys levels were greater when steers were fed diets containing AjiPro in comparison to when they were fed a negative control (NEGCON) which did not contain the product and was deficient in absorbable Lys. From both the in vitro dry matter degradation experiment and the 3 x 3 Latin Square study, we determined AjiPro to be an effective source of bypass Lys, and consequently used it to conduct a growing through finishing study. During Experiment 4, we evaluated steer performance when fed diets balanced for predicted Lys requirement to EE ratio through its supplementation in several dietary treatments. Control treatments included a negative control (NEGCON) that was deficient in absorbable Lys and contained no rumen-protected products; and a positive control (POSCON) where rumen-protected soybean meal was used to balance absorbable AA to EE ratio. Three additional dietary treatments included similar amounts of rumen-protected soybean meal and incremental amounts of AjiPro formulated to provide 50 percent (AJ50), 100 percent (AJ100), or 150 percent (AJ150) of the absorbable Lys provided by POSCON. Starting on d 151 of the growth study, steers were weighed on 2 consecutive days every 14 d and assigned a final BW when no longer profitable (defined as when cost of gain exceeded value of gain). Steers remained profitable for greater days for NEGCON, POSCON and AJ100 than AJ150. Steers consuming POSCON had lesser ADG (kg/d) than all other treatments during the early finishing phase (d 75 to 112). However, steer ADG (kg/d) during late finishing (d 112 to 179) was greater for steers fed diets optimized for Lys requirement (POSCON and AJ100) than all other treatments. Between d 112 to 179, POSCON had greater G:F than all other treatments but did not differ from AJ100. When encapsulated Lys was under or over-supplemented, finishing steers became less profitable sooner. Feed efficiency increased with use of rumen-protected products during late finishing (d 112 to 179) in diets formulated to meet Lys requirement, but this did not impact overall steer performance from growing through finishing. A more accurate understanding of steer AA requirement and subsequent AA metabolism will allow more precise and effective use of rumenprotected products.