Six bioassays were conducted to determine the ideal ratios of several amino acids relative to Lys. Young male crossbred chicks were fed diets based on corn gluten meal and synthetic amino acids that could be made singly deficient in Lys, Trp, Thr, Ile, or Val. Diets for all assays contained 3,400 kcal ME/kg, and L-glutamic acid was used to make all diets (within and among assays) equal in crude protein at 22.5% of the diet. True digestibility assessment of corn gluten meal in cecectomized roosters facilitated dose-titration studies so that least squares fitted one-slope broken-lines and quadratic regression equations could be calculated to establish inflection points for weight gain and gain:feed. Four battery pens of four chicks were fed one of six amino acid levels from 8 to 21 or 22 d posthatching. Weight gain and gain:feed responded quadratically (P < 0.01) to increasing doses of digestible Lys (0.68 to 1.28%), Trp (0.09 to 0.24%), Thr (0.41 to 0.81%), Ile (0.45 to 0.95%), and Val (0.51 to 1.06%). Broken-line least squares analysis predicted breakpoints for gain and gain:feed, respectively, of: Lys (0.85, 0.96%), Trp (0.16, 0.16%), Thr (0.53, 0.53%), Ile (0.59, 0.58%), and Val (0.74, 0.74%). The intercept of the quadratic regression curve and the plateau of the broken line predicted digestible Lys requirements for gain and gain:feed, respectively, of 0.95 and 1.03%. Similar calculations predicted digestible Trp requirements of 0.18% for gain and gain:feed, digestible Thr requirements of 0.59% for gain and 0.60% for gain:feed, digestible Ile requirements of 0.68% for gain and gain:feed, and digestible Val requirements of 0.81% for gain and 0.82% for gain:feed. Regardless of curve-fitting method, gain:feed requirements for Lys were much higher than weight gain requirements. Using the higher of the broken-line requirement estimates for gain and gain:feed, ideal ratios (% of Lys) were as follows: Lys (100), Trp (16.6), Thr (55.7), Ile (61.4), and Val (77.5).
Acid hydrolysis of dehulled soybean meal (SBM) and corn gluten meal (CGM) followed by chromatographic amino acid analysis (ninhydrin detection) revealed substantial quantities of S-methylmethionine (SMM) in both ingredients (1.65 g SMM/kg SBM; 0.5 g SMM/kg CGM). Young chicks were used to quantify the methionine- (Met) and choline-sparing bioactivity of crystalline L-SMM, relative to L-Met and choline chloride standards in 3 assays. A soy isolate basal diet was developed that could be made markedly deficient in Met, choline, or both. When singly deficient in choline or in both choline and Met, dietary SMM addition produced a significant (P < 0.01) growth response. In Assay 2, dietary SMM did not affect (P > 0.10) growth of chicks fed a Met-deficient, choline-adequate diet. A standard-curve growth assay revealed choline bioactivity values (wt:wt) of 14.2 +/- 0.8 and 25.9 +/- 5.1 g/100 g SMM based on weight gain and gain:food responses, respectively. A fourth assay, using standard-curve procedures, showed choline bioactivity values of 20.1 +/- 1.1 and 22.9 +/- 1.7 g/100 g SMM based on weight gain and gain:food responses, respectively. It is apparent that SMM in foods and feeds has methylation bioactivity, and this has implications for proper assessment of dietary Met and choline requirements as well as their bioavailability in foods and feeds.
A pig trial and a chick trial were done to determine the effect of high levels of Zn and Cu on the P-releasing efficacy of phytase. Ninety-nine individually fed pigs (7.2 kg) were given ad libitum access to one of 11 experimental diets for a period of 21 d. Fibula ash (mg) was regressed against supplemental inorganic P (iP) intake (g) to establish the standard curve, from which phytase treatments were compared to determine P-releasing efficacy. The basal diet was a corn-soybean meal diet with no supplemental P (21% CP, 0.075% estimated available P, 130 mg of Zn/kg, as-fed basis). Diets included three graded levels of supplemental iP (0, 0.075, 0.150%) from reagent-grade KH2PO4, two levels of phytase (500 and 1,000 FTU/kg) from EcoPhos, 1,500 mg of Zn/kg from either Waelz ZnO or basic Zn chloride (Zn5Cl2(OH)8), and all combinations of phytase and Zn. One phytase unit (FTU) was defined as the amount of enzyme required to release 1 micromol of iP per minute from sodium phytate at 37 degrees C and pH 5.5. Phytase supplementation improved (P < 0.01) weight gain, G:F, and fibula ash (% and mg). Bone ash (mg) was highest (P < 0.01) for pigs fed diets containing 1,000 FTU/kg of phytase. Supplemental Zn had no effect (P > 0.50) on growth performance, but decreased (P < 0.05) fibula ash (mg). Comparison of the phytase treatments to the standard curve (r2 = 0.87) revealed P-release values of 0.130 and 0.195% for 500 and 1,000 FTU of phytase/kg, respectively, in the absence of Zn, whereas in the presence of Zn (pooled), P-release values were decreased (P < 0.01) to 0.092 and 0.132%, respectively. The effects of high levels of supplemental Zn (basic Zn chloride) and Cu (CuSO4 x 5H2O) on phytase efficacy also were investigated in a 12-d chick trial. Dietary treatments were arranged according to a 2(3) factorial, with two levels each of supplemental phytase (0 and 500 FTU/kg from EcoPhos), Zn (0 and 800 mg/kg), and Cu (0 and 200 mg/kg). There was a phytase x Zn interaction (P < 0.01) for tibia ash. Thus, Zn supplementation decreased tibia ash in the presence, but not in the absence, of phytase. Supplemental Cu did not affect (P > 0.30) the response to phytase. These results suggest that pharmacological levels of Zn chelate the phytate complex, thereby decreasing its availability for hydrolysis by phytase.
Crossbred pigs (n = 1,400) were used to evaluate the effect of group size (25 vs 50 vs 100 pigs/pen) in a wean-to-finish production system on growth performance and carcass measures. Pigs were weaned at 17 d (range = 15 to 19) of age with a mean initial BW of 5.9 +/- 0.02 kg and taken to a final mean pen weight of 116 +/- 0.9 kg. A 10-phase dietary regimen was used, and pigs had free access to feed and water. Feeder-trough space (4.3 cm/pig) and floor-area allowance (0.68 m2/pig) were the same for all group sizes. Compared to groups of 25, pigs in groups of 50 and 100 animals were lighter (P < 0.001) at the end of wk 8 after weaning and had lower (3%, P < 0.01) ADG and gain:feed (G/F) but similar (P > 0.05) ADFI during the first 8 wk of the study. At the end of the study, pig weight and the coefficient of variation in pig weight within a pen were similar (P > 0.05) across group sizes. During the period from 8 wk after weaning to the end of the study, pigs in groups of 100 compared to 50 animals had greater (3%, P < 0.01) ADG, and pigs in groups of 25 were intermediate for ADG. Average daily feed intake during this period was similar (P > 0.05) for all group sizes; however, G/F was greater (3%, P < 0.01) for groups of 100 compared to 25 or 50 animals. For the overall study period, ADG, ADFI, and G/F from weaning to slaughter weight were similar across group sizes (P > 0.05; 655, 648, and 658 g; 1,759, 1,755, and 1,759 g; and 0.37, 0.37, and 0.37; for ADG, ADFI, and G/F, respectively, for groups of 25, 50, and 100 pigs, respectively). Mortality was similar (P > 0.05) across group sizes; however, morbidity (pigs removed due to poor health or injury) was higher in groups of 25 pigs compared to the other two group sizes (7.0, 3.5, and 3.9% for groups of 25, 50, and 100, respectively; P < 0.05). Group-size treatment did not affect (P > 0.05) carcass dressing percentage, backfat thickness, or loin-eye depth. In summary, growth performance from weaning to market weight was not affected by group size.
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