Phosphorus requirements of broiler chicks six to nine weeks of age as influenced by phytase supplementation.

Two trials of similar design were conducted to determine the nonphytate phosphorus (NPP) requirements for broilers from 42 to 63 d of age in diets with or without phytase supplementation. Male broilers of a commercial strain were grown to 42 d on nutritionally complete diets with NRC (1994) recommended levels of Ca and NPP. At 42 d, the birds were placed on experimental diets and fed to 63 d. The experimental treatments consisted of a 2 x 6 factorial arrangement with two levels of phytase (0 or 800 U/kg) and six levels of NPP (0.10 to 0.35% in 0.05% increments). Body weight gain, feed conversion, and mortality were determined during the period. At 49, 56, and 63 d, excreta samples were taken, and samples of birds were killed for tibia ash determination. The lowest level of NPP, with or without phytase supplementation, was sufficient for maximum BW gain, feed conversion, and livability. Using nonlinear regression, levels of NPP needed to optimize tibia ash in the absence of phytase were 0.31 +/- 0.004%, 0.23 +/- 0.02%, and 0.22 +/- 0.029% at 49, 56, and 63 d, respectively. When diets were supplemented with 800 U/kg of phytase, the NPP requirement for optimum tibia ash was 0.15 +/- 0.049% at 49 d. At 56 and 63 d, no more than 0.10% NPP (lowest level tested) was sufficient to maximize tibia ash. Compared to current NRC (1994) recommendations, the application of these reduced dietary phosphorus levels could markedly reduce excreta excretion of phosphorus by broilers.

Relationship of dietary lysine level to the concentration of all essential amino acids in broiler diets.

A study was conducted to evaluate the relationship of dietary Lys and other essential amino acids (EAA) in diets for broilers. Diets were formulated based upon NRC (1994) recommendations. Within each age period, diets contained NRC recommended levels of Lys with other EAA at 100, 110, 120, or 130% of NRC. The diets were then supplemented with 0.1, 0.2, or 0.3% additional Lys, resulting in a 4 x 4 factorial arrangement with four levels of Lys (NRC, + 0.1%, + 0.2%, and + 0.3% Lys) and four levels of other EAA (100, 110, 120, and 130% of NRC). Each of the 16 treatments was fed to six replicate pens of 25 male broilers of a commercial strain. At 56 d, five birds per pen were processed to determine dressing percentage and carcass yield. There were no significant interactions between level of Lys and levels of other EAA for live performance or carcass characteristics. The BW was significantly increased at 21 and 42 d by addition of + 0.1% Lys above NRC but not at 56 d. There was no significant effect of other EAA on BW at any age. The effects of Lys on feed conversion were varied. At 21 and 42 d, addition of 0.1% Lys to diets containing the NRC Lys level significantly improved feed conversion; response to 0.2 or 0.3% Lys were varied. No significant effects of Lys on feed conversion were observed at 56 d. Increasing the level of EAA resulted in significant improvements in feed conversion at 21, 42, and 56 d, generally following a linear trend. Dietary Lys levels had no significant effects on dressing percentage, breast meat yield, or abdominal fat content. The level of other EAA significantly influenced dressed yield but had no significant influence on carcass yield. These results indicate that NRC (1994) levels of Lys and other EAA are adequate for optimum performance of male broilers processed at 56 d but may be less than adequate at younger ages.

Evaluation of normal yellow dent corn and high available phosphorus corn in combination with reduced dietary phosphorus and phytase supplementation for broilers grown to market weights in litter pens.

A study was conducted to determine the extent fecal P levels could be reduced while maintaining performance. Various strategies were employed including the use of a high available phosphorus hybrid of corn (HAPC), supplementation with phytase enzyme, and reduced dietary P levels. The use of HAPC resulted in a 50% reduction in phytate-bound dietary P as compared with a normal yellow dent corn (YDC) diet. Dietary nonphytate P was maintained at either NRC (1994) recommendations for appropriate age periods or reduced by 0.075 or 0.15%. Portions of the diets were supplemented with 1,000 units of phytase/kg. Male chicks of a commercial strain were grown to 56 d on the test diets. Broilers fed diets with HAPC had BW, feed conversion, livability, and tibia ash that were equal to or superior to those fed diets with YDC with considerably reduced fecal P content at any dietary level of nonphytate P. Phytase supplementation enabled birds to maintain live performance at lower levels of nonphytate P, further reducing the fecal P output. One of the greatest contributions of phytase was a reduction in mortality at the lower levels of nonphytate P. Dietary P levels could be reduced by 0.075% under NRC (1994) recommendations without adversely affecting live performance; a reduction of 0.15% in conjunction with phytase supplementation maintained BW, feed conversion, and livability but reduced tibia ash. The extent to which dietary P levels can be reduced over the entire feeding program is subject to further research.

Nonphytate phosphorus requirement and phosphorus excretion of broiler chicks fed diets composed of normal or high available phosphate corn with and without microbial phytase.

A study was conducted to evaluate the ability of the young (0 to 3 wk) broiler chicken to utilize the P provided by a high available P corn [HAPC; 0.27% total P and 0.17% nonphytate P] in comparison with yellow dent corn (YDC; 0.23% total P and 0.03% nonphytate P), and to determine the extent to which supplementation with exogenous phytase enzyme could reduce the demands for dietary P and subsequently reduce P excretion. Diets prepared using the two types of corn differed in the amount of phytate-bound P, with the HAPC diets containing approximately 50% less phytate-bound P. Treatment diets were prepared by varying the amount of dicalcium phosphate, and ranged from 0.10 to 0.50% nonphytate P for YDC diets, and from 0.18 to 0.50% nonphytate P for HAPC diets. Sublots of each diet were supplemented with 800 units/kg phytase. Each diet was fed to six pens of five male chicks of a commercial broiler strain from 1 to 21 d of age. Regression analysis was used to estimate nonphytate P requirements for each corn type with and without phytase supplementation. The greatest need for nonphytate P was for maximum tibia ash, with requirements of 0.39, 0.29, 0.37, and 0.32% in diets with YDC, YDC plus phytase, HAPC, and HAPC plus phytase, respectively. Addition of phytase liberated approximately 50% of the phytate-bound P from each diet. These levels were sufficient to support body weight, feed conversion, and livability. Fecal P content of broilers fed diets with YDC at the NRC (1994) recommended level of 0.45% nonphytate P was 1.21%, whereas at the respective requirement points indicated above, the P content was 1.09, 0.87, 0.78, and 0.64% in feces from broilers fed diets with YDC, YDC plus phytase, HAPC, and HAPC plus phytase, respectively. Thus, fecal P output could be reduced while maintaining optimum performance by the use of reduced dietary nonphytate P, introduction of HAPC, and phytase supplementation. One of the greatest benefits of phytase supplementation appeared to be maintaining livability at lower dietary levels of nonphytate P.

Peripheral blood CD14(+) cells from healthy subjects carry a circular conformation of latent cytomegalovirus genome.

The majority of the human population harbors latent cytomegalovirus. Although CD14(+) peripheral blood mononuclear cells have been implicated as sites of latency, the conformation of the latent viral genome in these cells is unknown. In this study, the conformation of viral genomic DNA was assessed in CD14(+) cells from healthy virus seropositive carriers using an electrophoretic separation on native agarose gels in combination with polymerase chain reaction detection. Here we show that the viral genome migrates as a circular plasmid with a mobility equivalent to a circular 230-kb Shigella flexneri megaplasmid marker. Neither linear nor complex or integrated forms of the viral genome were detected. This report provides further evidence that the CD14(+) cell population is an important site of viral latency in the naturally infected human host. Detection of the viral genome as a circular plasmid during latency suggests that this virus maintains its genome in a manner analogous to other herpesviruses where latent viral genome conformation has been studied.

Effects of dietary vitamin E on the immune system in broilers: altered proportions of CD4 T cells in the thymus and spleen.

To gain insight into the immunomodulatory effects of vitamin E (VE), immune cell population analyses were conducted using thymus and spleen from male broilers fed diets with various levels of VE supplementation (0, 17, 46, and 87 mg dl-alpha-tocopherol acetate/kg of feed). At 2 and 7 wk of age, the percentages of B cells, macrophages, and T cell subsets, delineated by the expression of CD4, CD8, and T cell receptor (TCR) isotype, in thymus and spleen were determined by flow cytometry. The percentages of thymic and splenic B cells and macrophages from 2- and 7-wk-old chickens, as well as the percentage of thymic T cells in 2-wk-old chickens, were unaffected by VE treatment. However, 7-wk-old broilers maintained on 87 mg VE/kg feed had a higher percentage of CD4+CD8- thymocytes, a higher CD4+CD8- to CD4-CD8+ thymocyte ratio, and a lower percentage of CD4+CD8+ thymocytes than chickens receiving no dietary VE supplementation. The VE-induced increase in the percentage of CD4+CD8- thymocytes was due to an increase in the TCR2+CD4+CD8- thymocyte subset, whereas the decrease in the percentage of CD4+CD8+ thymocytes involved all TCR defined T cell subsets. In the spleen, the percentage of CD4+CD8- T cells was lower in 2-wk-old chickens and higher in 7-wk-old chickens maintained on 87 mg/kg feed than in chickens receiving no dietary VE supplementation. The decrease in CD4+CD8- splenocytes at 2 wk of age was due to a decline in the percentage of TCR2+CD4+CD8- splenocytes, whereas the increase in CD4+CD8- splenocytes in 7-wk-old chicks was due to an increase in the percentages of all TCR defined CD4+CD8- T cell subsets. These data support an immunomodulatory effect of VE on CD4+CD8- T cells.