Two hundred sixteen crossbred (PIC line 26 x Camborough 15) pigs were used in three trials to determine optimal digestible lysine levels during early (EF = 50 to 95 kg) and late (LF = 90 to 110 kg) finishing periods. Pigs were self-fed in sex groups of two in all trials. The assay diets for EF and LF periods were 11 and 10% CP corn-soybean meal diets, respectively, supplemented with threonine, methionine, tryptophan, valine, and isoleucine. Corn-soybean meal positive-control diets were included in each trial (14.5% CP for EF and 13.5% CP for LF). This dietary CP regimen was shown to give the same performance and carcass quality as a 17% CP corn-soybean meal diet fed during both EF and LF. Plateau portions of the lysine response curves resulted in performance levels that were equal to or greater than those achieved with pigs fed the 14.5/13.5% CP positive-control diets. Early-finishing pigs responded (P < .05) to graded doses of digestible lysine (.41 to .71%) for daily weight gain, gain:feed, longissimus muscle area, 10th-rib fat depth, lean gain, and plasma urea N. Digestible lysine requirement estimates based on average plateau points were .58% for EF barrows and .64% for EF gilts. Late-finishing pigs responded (P < .05) to digestible lysine doses (.35 to .65%) for daily weight gain, gain:feed, lean gain, and plasma urea N. Digestible lysine requirement estimates based on average plateau points were .49% for LF barrows and .52% for LF gilts.

In Exp. 1, young pigs were fed a basal diet containing .17% methionine (Met) (.14% digestible Met), and .48% cystine (.38% digestible cystine) for 14 d (34 to 48 d of age). Treatment additions were .25% DL-Met, .34% betaine, .30% choline, or .25% DL-Met and .34% betaine. Methionine, but not betaine or choline supplementation, increased (P < .05) weight gain and feed efficiency. Hepatic betaine-homocysteine methyltransferase (BHMT) activity was increased (P < .05) by betaine and choline supplementation but was not affected by Met deficiency. Renal BHMT activity was increased (P < .05) by Met deficiency and was further increased (P < .05) by betaine supplementation. In Exp. 2, 10-kg pigs were fed the basal diet from Exp. 1 supplemented with enough DL-Met to bring the total basal Met to .24% (.20% digestible Met). Treatment additions consisted of .20% DL-Met or .34% betaine, and diets were fed for 16 d (34 to 50 d of age). Feed efficiency increased (P < .05) in response to Met, but not to betaine, supplementation. Hepatic BHMT activity increased (P < .05) in response to betaine and Met, but no changes in renal BHMT activity occurred. Although statistically significant changes in hepatic and renal BHMT activity occurred in both experiments, the magnitude of the responses was probably not physiologically important. Therefore, in contrast to previous findings with rats and chicks, it does not seem that hepatic and renal BHMT activity in pigs is influenced substantially by Met deficiency, or by surfeit levels of choline or betaine.

Seven experiments were conducted to determine the efficacy of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] and microbial phytase in improving P, Zn and Mn utilization of chicks fed P, Zn- and Mn-deficient soy protein diets containing surfeit levels of cholecalciferol. Efficacy of 1 alpha-hydroxycholecalciferol (1 alpha-OH D3) was also studied. A dose titration study indicated that supplemental phytase at 1200 units/kg diet would increase bone ash by at least 65% when added to a corn-soybean meal diet containing 0.43 g P/100 g (0.1 g nonphytate P/100 g). These responses were similar to those obtained from supplemental P (0.1 g/100 g) as KH2PO4 or from added 1,25-(OH)2D3 (10 micrograms/kg). Dietary addition of both 1200 units phytase and 10 micrograms/kg 1,25-(OH)2D3 elicited bone ash responses that were near 100%. When chicks were fed a Zn-deficient soy-concentrate diet (13 mg Zn/kg), diet supplementation with 1,25-(OH)2D3 or phytase increased growth rate by 40% and tibia Zn content by > 100%; adding 1,25-(OH)2D3 together with phytase increased tibia Zn content by 160%. Utilization of both Zn and Mn contained in the corn-soybean meal diet also was markedly enhanced by supplemental phytase, 1,25-(OH)2D3, or the combination. The cholecalciferol analog 1 alpha-OH D3 was found to improve dietary P utilization maximally (70% bone ash response) at a dose of 20 micrograms/kg diet, and effects were additive when 1 alpha-OH D3 was fed in the presence of phytase.(ABSTRACT TRUNCATED AT 250 WORDS)

Commercial and laboratory-strain crossbred chicks responded (P < .01) markedly to 1alpha-hydroxycholecalciferol (1alpha-OH D3) during the 2nd and 3rd wk of life. Bone-ash responses exceeded 50% when this compound was added at 20 microg/kg to phosphorus (P)-deficient corn-soybean meal diets containing surfeit levels (25 microg/kg) of cholecalciferol (D3). Phosphorus excretion was decreased (P < .01) and, thus, retention was increased (P < .01) when 1alpha-OH D3 was supplemented. A P-deficient (.10% P) casein-amino acid purified diet, devoid of D3, was used to determine whether 15 microg/kg of D3 was sufficient to facilitate optimal absorption of the nonphytate P contained in this diet. Bone ash responded to .075% P addition (KH2PO4), and chicks fed diets with .175% nonphytate P exhibited further bone-ash responses to 15 microg/kg of D3 or 10 microg/kg 1alpha-OH D3. Higher levels of either of these D3 compounds did not produce additional responses. This suggested that 15 to 25 microg/kg of D3 in a P-deficient corn-soybean meal diet (.28% phytate P and .14% nonphytate P) is more than adequate to facilitate optimal absorption of the nonphytate P present in the diet. A P-deficient casein-dextrose diet (.13% nonphytate P and 15 microg/kg D3) was fed in the final chick assay, and chicks fed this diet did not show bone ash responses to 1alpha-OH D3 or to microbial-derived phytase (1,470 units/kg). Thus, with P-deficient corn-soybean meal diets containing at least 15 microg D3/kg, 1alpha-OH D3 supplementation markedly increased weight gain and bone ash because it increased the utilization of phytate P.

1. Three battery experiments were conducted with broiler chicks during the 2nd and 3rd week of life. Graded amounts of cholecalciferol (D3) were added to maize-soyabean meal diets that were designed to be (a) severely deficient in available phosphorus (P), (b) marginally deficient in calcium (Ca) or (c) adequate in both available P and Ca. 2. With diets containing 1.0 g available P and 6.3 g Ca/kg (assay 1), graded doses of D3 between 0 and 37.5 mu/kg produced linear (P < 0.05) positive responses in both weight gain and tibia ash. With a D3 concentration of 1250 micrograms/kg, 250 times the requirement recommended by the NRC, bone ash was increased (P < 0.05) over that of birds fed 37.5 micrograms/kg, and neither weight gain nor food intake were reduced. 3. With a P-adequate diet (4.5 g available P/kg) containing 8.5 g Ca/kg (assay 2), weight gain and bone ash increased linearly (P < 0.05) upon supplementing the basal diet with 0, 2.5 and 5.0 micrograms D3/kg. Higher doses of D3 did not elicit further responses, and chicks fed on a diet containing 1250 micrograms D3/kg gained as fast and had bone ash values that did not differ from those of chicks receiving 5, 10, 20 or 40 micrograms D3/kg. 4. When the maize-soyabean meal basal diet was fortified with Ca and P to achieve adequate amounts of Ca (10.1 g/kg) and P (4.5 g available P/kg) in assay 3, dietary additions produced results similar to those obtained in assay 2 where P was adequate and Ca was slightly deficient. Again, chicks receiving a surfeit of D3 (1250 micrograms/kg) exhibited weight gains and bone ash values that were as great as those of chicks receiving 5, 10, 15 or 30 micrograms D3/kg. 5. It is apparent that young chicks have a high tolerance for excess D3, and chicks fed on diets that are severely deficient in available P continue to respond to D3 in excess of 37.5 micrograms/kg.