Effect of dietary lysine on hepatic lysine catabolism in broilers.

Lysine is frequently a first- or second-limiting amino acid in poultry diets. Improving the efficiency of lysine use for protein synthesis would effectively lower the lysine requirement and decrease feed costs. Understanding how lysine is degraded and how the degradation is regulated would identify potential molecular targets for interventions to decrease lysine degradation. To better understand lysine degradation in poultry, 3 experiments were conducted. In experiment 1, one-day-old chicks were fed 1.07, 1.25, 1.73, or 3.28% dietary lysine for 2 wk. In experiments 2 and 3, fourteen-day-old chicks were fed 1.07 or 1.25% dietary lysine for 2 wk. Measures of liver lysine catabolism including lysine α-ketoglutarate reductase (LKR) and lysine oxidation (LOX) were assessed. The α-aminoadipate δ-semialdehyde synthase (AASS) is a bifunctional enzyme composed of both LKR and saccharopine dehydrogenase activities, and the relative abundance of this protein and mRNA were likewise assessed. Moreover, potential alternative pathways of lysine catabolism that depend on l-amino acid oxidase (AAOX) and on lysyl oxidase (LYLOX) were considered. In experiment 1, chicks fed lysine-deficient diets had decreased (P < 0.05) LKR activities compared with chicks fed at or above the requirement. However, the lowered LKR activities were not associated with a decreased (P > 0.05) LOX as measured in vitro. In experiments 2 and 3, chicks 28 d of age did not decrease LKR activity (P > 0.05) in response to a lysine-deficient diet. No changes in AASS protein abundance or mRNA were detected. Likewise, no differences in the mRNA abundances of AAOX or LYLOX were detected. The activity of AAOX did increase (P < 0.05) in birds fed a lysine-adequate diets compared with those fed a lysine-deficient diet. Based on kinetic parameters and assumed concentrations, AAOX could account for about 20% of liver lysine oxidation in avians.

The effect of feeding adequate or deficient vitamin B6 or folic acid to breeders on methionine metabolism in 18-day-old chick embryos.

Three isotopic tracers ([2,3,3-2H3]-L-serine, [2H11]-L-betaine, and [1-13C]-L-methionine) were administered by amnion injection into 18-day-old chick embryos to investigate the kinetics of methionine metabolism. The embryos utilized were from eggs collected from 34-week-old Cobb 500 broiler breeders that were fed either a control diet containing folic acid (1.25 mg/kg diet) and pyridoxine HCl (5 mg/kg diet) or diets devoid of supplemental pyridoxine or folic acid. Intermediate metabolites of methionine metabolism and polyamines were analyzed in 18-day-old chick embryos. There were no differences in hepatic [2H2] methionine or [2H3] cysteine enrichments or in physiological concentrations of sulfur amino acids for chick embryos from breeders fed the control diet and embryos from breeders fed diets containing no pyridoxine or folic acid. Supplementation of B6 or folic acid did not affect the production of methionine and cysteine in chick embryos. However, breeders fed the control diet with both folic acid and pyridoxine supplementation produced embryos with a two-fold reduction of hepatic homocysteine and increased spermine compared with embryos from breeders fed diets containing no supplemental pyridoxine or folic acid (P < 0.05). Hepatic S-adenosylmethionine for embryos from breeders fed no supplemental B6 was half the concentration compared with embryos from breeders fed the control diet. Embryos from breeders fed the control diet were utilized to determine the proportion of homocysteine going through remethylation and transsulfuration and also to determine the pathway of remethylation. Sixty-five percent of the methyl groups used for homocysteine remethylation from control embryos was via the MFMT pathway. Alternatively, 61% of homocysteine from control embryos was remethylated via the MFMT and the BHMT reactions and 39% of homocysteine was catabolized to cysteine via the transsulfuration pathway. These data show that in embryos, intermediate metabolites of methionine and polyamines increase in concentration when pyridoxine levels are provided in deficient concentrations to the breeder hen. In addition, this research demonstrates that folic acid deficient embryos conserve methionine, rather than catabolize it to cysteine.

Phytate phosphorus hydrolysis in broilers in response to dietary phytase, calcium, and phosphorus concentrations.

Three 5-d bioassays were conducted to investigate the microbial phytase effect on apparent phytate phosphorus (PP) hydrolysis by 21-d-old broilers using corn-soybean meal basal diets. In Experiment 1, broilers fed corn-soy basal diet [0.7% Ca, 0.4% total P (TP), and 0.12% nonphytate P (NPP)] with 0, 250, 500, 750, 1,000, 1,500, 2,000, and 5,000 FTU of phytase/kg diet produced PP hydrolysis (%) of 43.12, 68.12, 74.7, 85.02, 85.25 92.77, 96.91, and 99.45, respectively. In Experiment 2, broilers fed corn-soy basal (0.5% Ca and 0.17% PP) without added phytase and 0.08, 0.13, 0.18, 0.23, 0.28, 0.33, 0.38, and 0.45% NPP had PP hydrolysis (%) of 8.5, 27.6, 26.4, 28.9, 26.3, 17.1, 21.0, and 27.7, respectively. Broilers fed the same 0.5% Ca basal and NPP concentrations with 1,000 FTU of phytase/kg of diet increased (P < 0.05) PP hydrolysis (%) to 80.9, 75.9, 73.5, 72.2, 68.4, 71.6, 58.3, and 62.5, respectively. Experiment 3 was conducted in the same way as Experiment 2 but Ca was maintained at 0.9% for all diets. Phytate P hydrolysis (%) without addition of phytase in 0.08, 0.13, 0.18, 0.23, 0.28, 0.33, 0.38, and 0.45% NPP-fed groups was 49.2, 19.6, 16.0, 8.0, 9.4, 2.1, 4.0, and 4.2, respectively. The addition of phytase increased (P < 0.05) PP hydrolysis (%) to 85.3, 76.1, 70.0, 76.1, 62.6, 68.6, 67.4, and 63.7, respectively. In conclusion, these studies indicated near-complete hydrolysis (99.45%) of PP at greater dietary phytase (5,000 FTU/kg) supplementation, but maximum TP retention was obtained with only 1,000 FTU of added phytase. Maximum PP hydrolysis occurred for broilers fed diets with 1,000 FTU added phytase when the diets contained the lowest concentration (0.08%) of dietary NPP with either 0.5 or 0.9% dietary Ca concentrations. These data also suggest that broilers fed 0.9% dietary Ca have a greater P physiological threshold before a loss in retention compared with broilers fed lower (0.5%) dietary Ca concentrations with no dietary phytase supplementation.

Calcium particle size effects on plasma, excreta, and urinary Ca and P changes in broiler breeder hens.

An experiment was conducted using non-colostomized and colostomized broiler breeder hens to determine the effects of feeding limestone of 2 different mean particle sizes (185 microns and 3490 microns) on P excretion, total P and Ca retention, and urinary P and Ca excretion during a 6-week feeding study. Additionally, changes in plasma inorganic P (iP) and ionic Ca (Ca++) and urinary excretion of P and Ca were determined in one egg laying cycle of 24 hours. One-hundred-fifty non-colostomized and 6 colostomized broiler breeder hens, 30 wk of age, were divided into 2 groups and fed broiler breeder diets supplemented with either small particle or large particle limestone. Two % acid insoluble ash (Celite) was added to the feed as a marker. Diets, excreta, and urine samples were analyzed for total P and Ca by ionic coupling plasma (ICP) analysis. The non-colostomized breeders fed large particle limestone compared to small limestone particles produced a significant increase in percent tibia ash (P < 0.0001) and egg specific gravity (P = 0.0382), but P excretion approached a tendency of being reduced (P = 0.1585). The urinary total P and Ca (∼18 and 9%, respectively) of total P and Ca excretion for breeders fed both sizes of limestone was not significantly different in the colostomized breeders. In plasma, both iP and Ca++ reached a peak during 18 to 20 h and 20 to 24 h post oviposition for smaller and larger particle sized limestone fed groups, respectively. The maximal excretion of urinary P was found during 11 to 20 h post oviposition, whereas urinary Ca peaked during 0 to 11 h post oviposition for both smaller and larger particle sized limestone supplemented groups. In summary, the findings indicate that the particle size (smaller and larger) of calcium source did not significantly influence the quantitative total urinary excretion of Ca and P but did influence the timing of Ca and P excretion.

Improved colostomy technique and excrement (urine) collection device for broilers and broiler breeder hens.

In conducting nutritional experiments using chickens, scientists are limited in determining the urinary excretion of nutrients because of the difficulty of separating urine from feces. Our main objective was to improve the colostomy procedure for urine collection in broilers and both urine and egg collection for broiler breeder hens. Ketamine HCl (10 to 30 mg/kg i.m.) in combination with Xylazine (2 to 6 mg/kg i.m.) was used to anesthetize broilers (4 wk old) and broiler breeder hens (25 wk old). The colostomy technique involved: 1) transecting the distal colon at approximately 1.5 to 2 cm from the proximal cloaca and ligating the distal colonic segment with 3-0 absorbable surgical suture, 2) ligating the seromuscular coat of the colon to the peritoneal tissue at 3 points in a triangular shape using 4-0 silk suture, 3) ligating the mesentery at the skin level to prevent continued bleeding of the colostomy stoma, and 4) placing 3 sutures using a triangulation technique that consisted of the seromuscular aspect of the transected proximal colonic segment and the skin, and finally, 5) suturing all exteriorized edges of the transected proximal colonic segment after mucosal eversion to the skin with simple interrupted sutures using absorbable suture. For the purpose of urine or egg collection or both, the appropriate size of drainable pouch with a curved tail closure was used. Feces were collected on a tray. The colostomized broilers could be kept for several days and the colostomized broiler breeder hens for several months to collect urine, eggs (for breeder hens), and feces separately without the problem of cross-contamination.

The determination of retainable phosphorus, relative biological availability, and relative biological value of phosphorus sources for broilers.

A 10- to 21-d chick bioassay was conducted to determine the absolute retention value (ARV) for 2 different defluorinated phosphates (DF-1 and DF-2) and a reagent grade dicalcium phosphate (DCP). The total and test P in excreta regressed on feed P levels were subjected to general straight-line (linear), 1-slope broken-line, 2-slope broken-line, and polynomial regression methods to find the best analysis model. The relative biological availability (RBA) and relative biological value (RBV) for P from the 2 different defluorinated phosphates (DF-1 and DF-2) were obtained by the slope ratio method using 3 different bone measurements (% tibia ash, tibia breaking force, tibia weight) and RBV calculated using percentage tibia ash, weight gain, and feed/gain. The DCP was used as reference standard for RBA and RBV. The ARV measured at the breakpoints for test P by 2-slope analysis were determined to be 82.99% for DCP, 76.34% for DF-1, and 70.30% for DF-2. The ARV of test P determined at 0.45% NPP was 62.41% for DCP, 63.58% for DF-1, and 59.25% for DF-2. The relationship of ARV and RBA were similar in that DCP was 6% higher in ARV at the breakpoint compared with DF-1 and the RBA of DF-1 was 71 and 91% from tibia weight and tibia breaking force, respectively, compared with the bone parameters from chicks fed DCP. The DF-1 phosphate had 3 and 7% higher ARV at the breakpoint and 0.45% NPP, respectively, compared with DF-2. The RBA of DF-2 was 59 and 80% from tibia weight and bone-breaking force. The ARV of phosphate sources were independent of an arbitrary reference. The ARV for P sources provide retainable P information for industry-based feed formulation that can reduce excess P in poultry waste. The excreta P data from broilers fed increasing levels of DCP indicates that the data are best described statistically with a 1-slope broken-line regression, 2-slope broken-line regression, or polynomial regression.

Evaluation of increasing levels of a microbial phytase in phosphorus deficient broiler diets via live broiler performance, tibia bone ash, apparent metabolizable energy, and amino acid digestibility.

The objective was to investigate increasing concentrations of an evolved microbial phytase on male broiler performance, tibia bone ash, AME, and amino acid digestibility when fed diets deficient in available phosphorus (aP). Experiment 1 evaluated the effects of phytase during a 21 d battery cage study and Experiment 2 was a 42 d grow-out. Experiment 1 included six treatments; negative control (NC) with an aP level of 0.23% (starter) and 0.19% (grower), two positive controls (PC) consisting of an additional 0.12% and 0.22% aP (PC 1 and PC 2), and the NC supplemented with three levels of phytase (250, 500, and 2,000 U/kg). The NC diet reduced (P < 0.05) FC, BW, and bone ash. Phytase increased (P < 0.05) BW with 2,000 U/kg phytase yielding similar results to the PC2, and improved FCR and increased bone ash was observed at all phytase levels. Amino acid digestibility coefficients were increased (P < 0.05) with phytase at 250 U/kg. Phytase at all rates increased (P < 0.05) AME to levels similar level as PC diets. Linear regression analysis indicated average P equivalency values for BW and bone ash of 0.137, 0.147, and 0.226 for phytase inclusion of 250, 500, and 2000 U/kg, respectively. Experiment 2 included a PC consisting of 0.45%, 0.41%, and 0.38% aP for the starter, grower, and finisher, respectively; NC with reduced aP of 0.17%; and phytase at 500 and 2,000 U/kg. Phytase increased BW (P < 0.05) compared to the NC as 2,000 U/kg phytase resulted in further BW increases compared to the PC (starter and grower). Phytase improved FCR to levels comparable to the PC, with supplementation at 2,000 U/kg resulting in improvements beyond the PC in the starter phase. Amino acid digestibility coefficients were increased with phytase at 2,000 U/kg to levels comparable to that of the PC. These data confirm that the inclusion of phytase improves broiler performance and bone mineralization in aP reduced diets and levels beyond the traditional 500 U/kg can result in further improvements.