Eight digestion trials were conducted with pigs fitted with ileal T-cannulas to determine the apparent digestibilities of N and amino acids in common protein feedstuffs. Trial-to-trial variation was minimal as determined by the variation in digestibilities for soybean meal, which was evaluated in each trial. Apparent digestibilities varied widely; ileal N digestibility ranged from 88 to 63%, and ileal lysine digestibility ranged from 93 to 40%. In general, ring-dried blood meal, corn gluten meal, Menhaden fish meal, poultry-by-product meal and extruded whole soybeans were the most digestible, followed by canola meal, sunflower meal, peanut meal and meat and bone meal. Cottonseed meal and feather meal were the least digestible. Mean values for each feedstuff agree well with published data. Variation in digestibilities among samples of the same feedstuff was greater for the meat and bone meals. Regression of ileal essential amino acid digestibilities on ileal and fecal N digestibility indicated that amino acid digestibilities can be predicted more precisely from ileal N digestibility than from fecal N digestibility. However, neither ileal nor fecal N digestibility could be used with a high degree of certainty to predict ileal amino acid digestibilities.

Growth and digestion experiments were conducted to estimate the digestible P needs of terminal-cross growing-finishing pigs fed sorghum-soybean meal-based diets from 25 to 118 kg. Dietary available P levels approximated the levels recommended by the NRC (1988) or were approximately 25% above or below those levels. Up to 80 kg, dietary treatment did not affect performance; from 80 to 118 kg, the lowest P level (no inorganic P) reduced (P = .03) feed efficiency. Carcass leanness, subjective quality scores for the loin, chemical content of lean, and sensory evaluation of cooked lean were not adversely affected by decreasing P. As dietary P decreased, connective tissue amount in the lean decreased (P = .06). Ash content (P < .01) and peak load (P < .05) of metacarpals and metatarsals decreased as dietary P decreased, but structural soundness scores in the live pig were unaffected by treatment. Apparent digestibility of P decreased (P = .08 to P < .01) as dietary P decreased in the diets. Estimated P excretions per pig decreased with decreasing dietary P up to 80 kg; during the 80-to-118-kg interval, P excretions were similar for pigs fed the two lowest P diets due to reduced feed efficiency of pigs fed the lowest P diet. Dietary digestible P contents maximizing performance and carcass merit were .21, .19, and .16% for pigs fed from 25 to 50, 50 to 80, and 80 to 118 kg, respectively. The results suggest that P excretions of terminal-cross pigs can be reduced by feeding less than current NRC recommendations for P without reducing performance, carcass merit, or structural soundness of live pigs.

The efficacy of a recombinantly derived microbial phytase (Natuphos 5000, BASF Corp.) was evaluated in sorghum-soybean meal-based diets of finishing swine. During the 50- to 80- and 80- to 118-kg BW intervals, diets contained .40 and .39% plant P, respectively; control diets fed during the two weight intervals were supplemented with .08 and .04% inorganic P from dicalcium phosphate. The all plant-P diets were supplemented with 0, 300, or 500 phytase units (FTU) per kilogram of diet. Supplemental P (P = .09) and phytase (linear, P = .01) increased growth rate but did not affect feed efficiency. Dietary treatment did not affect quantitative carcass traits, CP, fat, or moisture content of the loin or taste panel scores of the cooked loin other than a quadratic decrease (P = .02) in connective tissue amount as phytase supplementation increased. Apparent ileal and total tract digestibilities of DM, GE, and N were not affected (P > .25) by phytase supplementation, whereas ileal and total tract digestibilities of Ca and P increased (P < .05 or P < .01) with increasing phytase supplementation. Ultimate load and ash content of the third and fourth metacarpals and metatarsals and serum P levels increased in response to inorganic P and phytase supplementation. Pig performance, carcass traits, and bone traits were essentially equal for the 300 and 500 FTU/kg treatments. These results show that phytase effectively liberates P in sorghum-based diets, and that 300 FTU/kg (or less) will optimize performance and carcass merit of finishing swine.

The digestible threonine (Thr) requirements of starter (28 d of age initially, 6 to 16 kg) and finisher (58 to 96 kg) pigs were determined. Each growth trial evaluated control and basal diets and the basal diet plus four incremental additions of L-Thr (.60 to .76% dietary Thr for starter pigs and .30 to .50% dietary Thr for finisher pigs). The basal diet fed to starter pigs contained 17.6% CP and 1.25% lysine and was based on sorghum, peanut meal, soybean meal, and dried whey. The basal diet fed to finisher pigs contained 9.7% CP and .75% lysine and was based on sorghum supplemented with lysine, methionine, tryptophan, and isoleucine. Incremental increases in dietary Thr increased (P < .05) ADG and ADFI of starter pigs quadratically. Gain/feed increased (P < .01) linearly. Based on broken-line regression analyses, .63% Thr maximized ADG of starter pigs. Daily gain and gain/feed of finisher pigs increased linearly (P < .01) and quadratically (P < .01) as dietary Thr content increased. Broken-line regression analyses determined that .41% Thr maximized ADG and gain/feed. Digestion trials with pigs fitted with an ileal T-cannula determined that the basal starter and finisher diets contained .43 and .17% apparent ileal digestible Thr and 3.35 and 3.38 Kcal of fecal DE/g, respectively. On average, crystalline Thr had an apparent ileal digestibility of 98%. Based on these values and the total Thr requirements given above, the digestible Thr requirement of finisher pigs for maximum ADG and gain/feed was estimated to be .28%.(ABSTRACT TRUNCATED AT 250 WORDS)

Seven hundred eight crossbred pigs were used in growth and digestion trials to determine the digestible tryptophan (Trp) requirement of starting (6 to 16 kg), growing (22 to 50 kg), and finishing (55 to 97 kg) pigs. Each growth trial evaluated a corn-fish meal-corn gluten meal basal diet, the basal diet with five incremental additions of L-Trp, and a control corn-soybean meal diet. The tryptophan content of the six incremental diets ranged from .13 to .255% for starting pigs, .08 to .18% for growing pigs, and .063 to .163% for finishing pigs. Lysine contents of basal diets were 1.38, .90, and .72% for starting, growing, and finishing diets, respectively. In all trials, ADG, ADFI, and gain/feed increased (P less than .001) linearly and quadratically as dietary Trp increased. Broken-line regression analyses determined the total dietary Trp requirements needed to optimize performance to be .19, .13, and .09% (as-fed basis) for starting, growing, and finishing pigs, respectively. These concentrations equated to Trp intakes of .96, 2.18, and 2.88 g/d. A digestion trial using growing pigs (29 kg initially) determined the apparent ileal digestibility of Trp in the basal starting and growing diets to be 72 and 70%, respectively; a similar trial with finishing pigs (55 kg initially) found 59% Trp digestibility for the basal finishing diet. Mean digestibility of L-Trp was 97%. Based on these values and the total Trp requirements given above, the digestible Trp requirements are .15, .10, and .06% for starting, growing, and finishing pigs, respectively.