Effects of high non-phytate phosphorus starter diet on subsequent growth performance and carcass characteristics of broiler chickens.

The trial was performed to investigate the effects of different concentrations of non-phytate phosphorus (nPP) in the starter and grower (with phytase inclusion) periods on carcass characteristics, organ weight and weekly variations of growth performance in the grower period. Seven hundred and twenty-day-old male broiler chickens were randomly assigned to 12 treatments in a completely randomized design. Chickens received two dietary treatments (4.5 g/kg and 6 g/kg nPP) in the starter (0-21 days) and six experimental diets (4 g/kg, 3.1 g/kg, 2.3 g/kg and 2.3 g/kg + 1000 FTU/Kg of feed phytase, 1.5 g/kg, 1.5 g/kg nPP + 1000 FTU/Kg of feed phytase) in the grower period (22-42 days). Results showed that phytase inclusion in the second and third weeks of grower period could increase feed intake significantly. Also, decrease in the concentrations of nPP to 1.5 g/kg caused to decline body weight gain markedly. Moreover, there is a significant difference between 4.5 g/kg and 6 + 4 g/kg nPP (starter+grower) and 1.5 g/kg nPP. Phytase inclusion increased carcass yield and declined liver weight significantly. Dietary treatment of 4.5 + 1.5 g/kg nPP enhanced heart and liver weight markedly. It is concluded that starter diets with increased concentration of nPP (6 g/kg nPP) had no beneficial effects on growth performance in the starter and grower period in the total (0-42 days). Also, it is possible to decrease nPP concentration of grower diets to 1.5 and 2.3 g/kg with and without phytase inclusion respectively.

Interactions between phytase and xylanase enzymes in male broiler chicks fed phosphorus-deficient diets from 1 to 18 days of age.

A total of 735 one-day-old male broiler chicks were used to evaluate the interactions between different levels of phytase and xylanase enzymes on performance and bone mineralization. Basal nonphytate P (nPP)-deficient diets (0.15%) were supplemented with different levels of phytase [0X, 1X, 2X, 3X, and 4X of recommended level (X = 500 phytase units per kg of feed)] alone or in combination with 3 levels of a xylanase preparation [0X, 1X, and 2X of recommended level (X = 0.1 g per kg of feed; a mixture with predominantly xylanase activity)]. A standard curve was developed using different levels of nPP (0.15 to 0.45%) to estimate the P equivalency of each enzyme combination. Treatments were replicated with 7 pens of 5 chicks each. The findings indicated that reducing dietary nPP level had a severely negative influence on bird performance and bone ash content. Results also showed that increasing levels of phytase significantly (P < 0.05) improved BW, feed intake, feed conversion ratio, mortality, and toe and tibia bone ash contents in a dose-dependent fashion. The P equivalency of phytase was also dose dependent, with estimates of 0.08, 0.11, 0.15, and 0.19 for 1X, 2X, 3X, and 4X supplementation levels of phytase, respectively. Xylanase preparation at 1X level failed to influence measured criterion; however, increasing the level of xylanase (2X) resulted in deteriorating BW and feed conversion ratio. The P equivalency of xylanase preparation at 1X and 2X was estimated as 0.010 and 0.014%. There were no interactions between phytase and xylanase preparation (P > 0.05). In conclusion, phytase was effective in improving bird performance and bone mineralization; however, xylanase supplementation failed to enhance phytase efficacy.

Assessment of potential enhancing effects of a carbohydrase mixture on phytase efficacy in male broiler chicks fed phosphorus-deficient diets from 1 to 18 days of age.

A total of 540 one-day-old male broiler chicks were used to evaluate the potential enhancing effects of a mixture of 2 commercial carbohydrase preparations on phytase efficacy. A nonphytate phosphorus (nPP) deficient diet (0.15%) was supplemented with different levels of phytase (0X, 1X, 2X, and 3X of recommended level of 500 phytase units per kg of feed), individually or in combination with different levels of a mixture of 2 commercial carbohydrase enzymes [0X, 1X, and 2X of recommended level (X = 0.2 g per kg of feed; a mix with predominantly xylanase and ß-glucanase activity)] to determine their effects on performance and bone development. A standard response curve was developed using graded levels of nPP (0.15 to 0.45%) from dicalcium phosphate in a diet with no phytase supplementation to estimate the phosphorus equivalency of the different enzyme combinations. Each diet was fed to 6 replicate pens of 5 male chicks from 1 to 18 d of age. Phytase at normal usage levels of 500 phytase units per kg of feed was effective (P < 0.05) in improving BW, increasing feed intake, reducing mortality rate, and increasing toe and tibia ash without significantly influencing feed conversion. Addition of extra levels of phytase (2X and 3X) significantly (P < 0.05) improved toe and tibia ash without further affecting performance traits. The carbohydrase mixture failed to improve performance or enhance phytase efficacy. The phosphorus equivalency of phytase was dose dependent, with estimates of 0.100, 0.123, and 0.213% for 1X, 2X, and 3X supplementation levels of phytase, respectively, based on tibia ash. In conclusion, results indicate that increasing the level of phytase resulted in significant improvements in utilization of dietary nPP, whereas the carbohydrase preparation had no significant effects on performance or had limited effects in enhancing phytase ability in young broiler chicks.

Effect of different levels of dietary vitamin E (DL-α-tocopherol acetate) on the occurrence of various degrees of white striping on broiler breast fillets.

White striping could be a potential reason for the rejection of raw breast fillets in the market. The condition is characterized grossly by the white striations occurring on the fillets showing myopathic changes on microscopic examination. Early research has shown similar lesions in the case of nutritional muscular dystrophy, which is a condition caused mainly by the deficiency of vitamin E in the diet. The present study was intended to evaluate the effect of different levels of dietary vitamin E (dl-α-tocopherol acetate) on the incidence of normal, moderate, and severe degrees of white striping, by modern description, on broiler breast fillets. Basal diets adequate for starter (0 to 18 d), grower (19 to 32 d), and finisher (33 to 49 d) age periods supplemented with 15, 50, 100, 200, and 400 IU of vitamin E/kg of feed were used in the study. Each of the 5 diet treatments were fed to 8 pens (53 birds each) of male broilers from a commercial strain. At 49 d, 5 birds were randomly selected from each pen (n = 40 birds/diet treatment) and were processed. Live weight, ready-to-cook weight, weight of the fillets, wings, tenders, legs, and the racks were obtained. The fillets were scored for the 3 degrees of white striping. There were no significant differences among the diet treatments with respect to the weight and carcass yield parameters. Furthermore, the diet treatments did not show any significant effect on the occurrence of normal, moderate, and severe degrees of white striping. However, fillet weight was the only parameter that had a significant effect on the occurrence of white striping. Higher degrees of white striping were seen associated with heavier fillets, which is in accordance with previous studies. Different levels of vitamin E levels used in the present study did not show any significant effect on the occurrence of 3 degrees of white striping. These results suggest that dietary vitamin E level is not associated with the modern condition of white striping in broiler breast meat.

Influence of growth rate on the occurrence of white striping in broiler breast fillets.

White striping refers to the occurrence of different degrees of white striations on broiler breast fillets and thighs of larger broilers, yet little is known about its causes. Thus, the objective of the study was to estimate the occurrence of normal (NORM), moderate (MOD), and severe (SEV) degrees of white striping with respect to the growth rate of broilers and to compare their proximate composition without the confounding effect of diet. Straight-run 1-d-old chicks (n = 280) were randomly assigned to either a low- (LED) or high-energy (HED) diet (5 replicates of 28 birds/dietary treatment). Birds were processed at 54 d of age, and live weight, deboned fillet weight, and occurrence of white striping were recorded. As expected, birds fed the HED had lower (P < 0.05) feed conversion ratios than birds fed LED (2.08 vs. 2.28). Also, HED-fed birds had heavier P < 0.05) live and fillet weights when compared with the LED-fed birds. A greater (P < 0.05) percentage of breast fillets from LED-fed birds were scored NORM, whereas HED-fed birds produced a greater (P < 0.05) percentage of SEV fillets. Fillet weight and yield (percent of live weight) increased (P < 0.05) as the degree of white striping increased from NORM to SEV. Additionally, NORM fillets had greater (P < 0.05) lipid and lower (P < 0.05) protein content when compared with SEV fillets. Also, NORM fillets had greater (P < 0.05) percentages of SFA than SEV fillets; however, proportions of all monounsaturated fatty acids, as well as linoleic and linolenic acids, were greater (P < 0.05) in SEV than NORM fillets. These results suggest that an increased growth rate results in increased occurrence of higher degrees of white striping in broiler breast fillets, and the various degrees of white striping are associated with differences in chemical composition of breast fillets.

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.

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

Two studies of identical design were conducted in battery brooders utilizing male chicks of a commercial strain. The birds were grown to 3 wk on diets with adequate P and from 3 to 6 wk were fed diets ranging from 0.10 to 0.45% nonphytate P (nPP) in increments of 0.05%, with or without supplementation with 800 units of phytase per kilogram of diet. Measurements included BW gain, feed conversion ratio (FCR), mortality, tibia ash, and fecal P content. Nonlinear regression was used to estimate nPP needs for optimizing BW gain, feed conversion, and tibia ash. In the absence of phytase, nPP levels of 0.33, 0.186, and 0.163% were required to optimize tibia ash, BW gain, and FCR, respectively. The estimated level for optimum tibia ash is in close agreement with current NRC (1994) recommendations. In the presence of 800 units of phytase per kilogram, nPP levels of 0.24, 0.151, and 0.109% were needed to optimize tibia ash, BW gain, and FCR, respectively. Fecal phosphorus levels were markedly reduced at the lower P levels. Further studies are needed to determine whether maximum tibia ash values are needed to sustain optimum production of market broilers.

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.

Nutritional approaches to reducing phosphorus excretion by poultry.

Phosphorus is an essential mineral for growing poultry, and the consequences of a failure to provide for adequate quantities of this nutrient are physiologically and economically disastrous. Therefore, nutritionists provide a margin of safety for this mineral in their diets. However, because of growing concerns regarding the potential contribution of P in poultry excreta on eutrophication of surface waters, increasing pressure is being placed to limit the amount of excess P in diets and thus reduce fecal output. In order to significantly reduce fecal P while maintaining economic productivity, the nutritionist must establish and maintain an integrated program of activities, including an effective quality control program for incoming animal protein feeds, selection of P supplements of the highest biological value, use of phytase enzymes, and judicious selection of dietary P levels. Potential benefits of newer isomers of vitamin D and the commercial development of grains with high levels of nonphytate P offer promise in the future. Whatever measures are taken to increase the biological availability of the phytate-bound and nonphytate P portions of the diet, commensurate reductions in overall dietary P content must be made.

Dietary arginine and lysine in Large White toms. 1. Increasing arginine:lysine ratios does not improve performance when lysine levels are adequate.

A study was conducted utilizing two strains of male Large White turkeys (BUT Big 6 and Nicholas 700) to determine the effects of increasing Arg:Lys ratios on live performance and carcass composition. Diets were formulated to provide 100, 110, and 120% of NRC (1994) Lys levels, adjusted for dietary energy level, with Arg:Lys ratios of 1.0:1, 1.1:1, 1.2:1, and 1.3:1 in a 3 x 4 factorial arrangement. Eight pens of 15 poults (four pens of each strain) were fed each of the 12 test diets for an 18-wk period. Diets were changed at 3-wk intervals rather than the 4-wk interval suggested by NRC. The results of this study suggest that the Arg and Lys levels suggested by the NRC (1994) are not sufficient when diets are fed on 3-wk intervals, rather than the 4-wk intervals suggested by NRC. This conclusion is in agreement with the studies of Waldroup et al. (1997b). Increasing Arg:Lys ratios improved performance of turkeys only when the diets contained insufficient amounts of Arg in association with low levels of Lys. Increasing Arg:Lys ratios when diets contained sufficient amounts of these two amino acids was without benefit, in contrast to the report of Brake et al. (1994). Turkeys of the BUT Big 6 strain appeared to be more sensitive to marginal deficiencies of Lys and Arg than did turkeys of Nicholas 700 strain.

Utilization of spent hen meal in diets for broiler chickens.

Studies were conducted to evaluate spent hen meal (SHM) produced in commercial rendering plants as a nutrient source in diets for broiler chickens. Utilizing previously determined nutrient composition values, including digestible amino acid and TMEn content, diets were formulated to include 0, 5, 10, and 15% of SHM from three different locations. In the first experiment, conducted in battery pens from 1 to 21 d posthatch, diets were formulated with digestible amino acid requirements set at 90, 95, or 100% of NRC (1994) total amino acid requirements. In the second experiment, conducted in floor pens from 1 to 49 d posthatch, diets were formulated with digestible amino acid requirements set at 95% of NRC (1994) total amino acid requirements. Samples of birds from the second experiment were processed to determine the possible influence of SHM inclusion on carcass yield. Results of the present studies indicate that SHM from commercial rendering facilities can be utilized in diets for growing broiler chickens provided adjustments are made in nutrient content and digestibility. When formulated on the basis of digestible amino acid content, levels of SHM up to 10% appear acceptable based upon body weight, feed conversion, bone ash, and carcass yield. Higher inclusion rates generally reduced performance. It is apparent that differences in nutritional quality may exist among products produced by different rendering facilities; however, evaluation of products to assess nutrient quality may be difficult under commercial conditions. As more information is generated regarding typical amino acid content and digestibility of rendered SHM, the product may be used with greater confidence in commercial diets.

An evaluation of threonine requirements of young turkeys.

Two experiments were conducted to evaluate the Thr requirements of male Large White turkeys from 3 to 6 and 6 to 9 wk of age. One group of turkeys was fed to 3 wk using nutritionally adequate diets and fed test diets from 3 to 6 wk; another group of turkeys was fed to 6 wk using nutritionally adequate diets and fed test diets from 6 to 9 wk. Test diets were composed of peanut meal, soybean meal, corn, and grain sorghum as intact protein sources and were supplemented with amino acids. Peak performance of turkeys fed the test diets was equivalent to that of turkeys fed conventional corn-soybean meal diets formulated to meet NRC (1994) standards. Estimates of Thr requirements for weight gain were 0.92 and 0.86% for 3 to 6 and 6 to 9 wk, respectively. For feed conversion, estimates of Thr requirements were 0.87% and 0.84% for 3 to 6 and 6 to 9 wk, respectively. The results of the two experiments reported herein would suggest that the Thr requirements suggested by NRC (1994) for turkeys up to 9 wk of age are safe estimates; they may slightly overestimate the requirements but not by a large margin.

Effects of amino acid restriction during starter and grower periods on subsequent performance and incidence of leg disorders in two strains of male large white turkeys.

Male turkeys of two commercial Large White strains (Nicholas 88, BUT 6) were subjected to growth restriction by means of reducing amino acid (AA) content of diets to a minimum of 75% of NRC (1994) suggested levels. There were three periods when diets containing 75% of NRC recommended AA for that age period were fed ad libitum: 0 to 3 wk, 0 to 6 wk, or 6 to 12 wk. A fourth (control) group was not restricted in AA content at any time. When turkeys were not fed the AA-restricted diets they were fed diets formulated to meet a minimum of 100, 110, or 120% of NRC (1994) AA recommendations, which resulted in a 3 x 4 factorial arrangement of treatments with three AA levels by four restriction times. Four pens of 12 males each were fed each AA by restriction time combination. At 18 wk, all birds were scored individually for leg condition and representative samples of turkeys were processed for parts yield. Birds fed restricted diets from 0 to 6 or 6 to 12 wk had significantly lower BW at 18 wk than control birds. Birds fed the restricted diets from 0 to 3 wk did not differ significantly in 18-wk BW compared to control birds but the magnitude of difference was similar to that observed at the end of the restriction period. Feed utilization was not improved by early AA restriction. Restricting early growth resulted in a significantly higher incidence of birds with no leg disorders and a lower incidence of birds with moderate leg disorders than control birds. Feeding higher AA levels during realimentation resulted in a greater severity of leg disorders. Breast meat yield was depressed significantly as severity of early restriction increased. Increasing dietary AA above NRC (1994) recommended levels generally improved performance during realimentation but was not able to compensate for reduced gains during restriction.

Effect of dietary phytase and high available phosphorus corn on broiler chicken performance.

Two trials were conducted to determine the effects on broiler chicken performance and health of reducing dietary phosphorus levels by treating feed with the enzyme phytase, formulating diets using high available phosphorus (HAP) corn, or when diets were formulated with HAP corn and treated with phytase. Cobb x Cobb male broiler chickens were placed in an experimental design consisting of four dietary treatments with six replicate pens of 50 broilers per pen. The dietary treatments consisted of untreated control feed, phytase-supplemented feed (500 U/kg), diets prepared with HAP corn, and diets prepared with HAP corn and supplemented with phytase. The chickens were maintained on these dietary treatments from 1 to 49 d of age with feed and water made available for ad libitum consumption. When the two trials were combined, there was a significant (P < or = 0.05) increase in body weight in the broilers fed the phytase treated diets at 49 d of age. The serum activity of alkaline phosphatase was significantly decreased in the diets supplemented with phytase, and serum cholesterol was significantly decreased in the diets prepared with HAP corn. These data indicate that total phosphorus can be reduced by at least 11% in diets prepared with HAP corn, or in diets supplemented with phytase, without affecting the performance or health of broiler chickens. When diets are prepared with HAP corn and supplemented with phytase, the dietary addition of total phosphorus can be reduced by at least 25% without affecting broiler chicken performance or health.

Response of two strains of large white male turkeys to amino acid levels when diets are changed at three- or four-week intervals.

A study was conducted to evaluate the amino acid recommendations of the NRC (1994) when diets were changed at 3- or 4-wk intervals. Diets formulated to provide from 90 to 115% of recommended amino acid levels were fed to Nicholas (NIC) and British United Turkey (BUT) Large White males from day-old to 24 wk of age; samples of turkeys were processed at 18 and 24 wk. Results indicated that the amino acid levels suggested by NRC are adequate to support maximum body weight gain, feed conversion, and dressing percentage of Large White males grown to 18 or 24 wk when fed on 4-wk intervals. An approximately 5% higher level of amino acids was required to maximize breast yield. When feeds were changed at 3-wk intervals, higher levels of amino acids were required to maximize performance; however, there did not seem to be any difference in the response of the two strains of turkeys to different levels of amino acids in this study.

Performance and carcass composition of large white toms as affected by dietary crude protein and threonine supplements.

This experiment evaluates the effect of decreasing dietary CP, in addition to the effects of dietary supplements of L-Thr to low CP diets, in Large White Nicholas toms from 0 to 18 wk of age. Toms were fed dietary treatments consisting of four levels of dietary CP as a percentage of NRC (1994) recommendations (100, 92, 84, and 76% of NRC recommendations). Additional treatments consisted of supplements of L-Thr (0.1 and 0.2% of diet) added to the 92 and 84% NRC CP treatments. All eight dietary treatments were formulated to meet a minimum of 105% of NRC (1994) recommendations for Met, TSAA, Lys, Thr, and Trp. Body weight, feed conversion, mortality, and carcass composition responses were measured. Decreasing CP to 84% of NRC resulted in 18-wk BW lower than that (P < or = 0.001) of toms fed diets containing 100 or 92% of NRC CP; however, toms fed 84% of NRC CP diet supplemented with 0.1% L-Thr had 18-wk BW equal to (P < or = 0.001) that of the 100 and 92% NRC CP treatments. Toms fed diets containing 76% of NRC CP had depressed BW and feed:gain in comparison to all other treatments. No adverse effects in cumulative feed:gain (0 to 18 wk) were noted by decreasing CP from 100 to 84% of the NRC recommendations. Mortality did not differ among treatments. Treatments had no effect on carcass fat expressed as a percentage of hot carcass weight. Breast meat yield (deboned Pectoralis major and Pectoralis minor) was highest (P < or = 0.001) in toms fed the 100 and 92% NRC CP treatments. The 84 and 76% NRC CP treatments resulted in decreased breast meat yield regardless of L-Thr supplements. These results indicate that diets containing Met, TSAA, Lys, Thr, and Trp at a minimum of 105% NRC recommendations may support favorable breast meat yield when CP is decreased to 92% of the NRC (1994) recommendation. If growth and feed conversion are the desirable traits, rather than breast meat yield, CP levels below 92% of the NRC (1994) recommendation may support favorable responses.

Evaluation of National Research Council amino acid recommendations for large white turkeys.

Two trials of identical experimental design were conducted to evaluate the NRC (1994) amino acid requirements for growing turkeys. Diets were formulated for 4-wk age intervals using intact ingredients and amino acid supplements to provide 85, 90, 95, 100, 105, 110, 115, and 120% of the suggested requirements. Formulation was done in a manner to minimize excess levels of as many essential amino acids as possible. Day-old male poults of a commercial Large White strain were grown to 20 wk on the test diets with body weight and feed conversion determined at intervals throughout the test; representative samples of birds were processed to determine carcass composition and parts yield. Results suggested that diets formulated to provide 105% of the suggested NRC requirements were needed to provide maximum body weight gain, feed conversion, and breast meat yield. Ambient temperatures in the present study frequently exceeded 27 C and may have contributed to the need for somewhat greater amino acid needs than the present NRC (1994) suggestions.

Influence of dietary lysine levels and arginine:lysine ratios on performance of broilers exposed to heat or cold stress during the period of three to six weeks of age.

Four trials of identical experimental design were conducted to determine the effects of temperature, dietary Lys level, and dietary Arg:Lys ratios on performance and carcass yield of male broilers. Birds of a commercial strain were grown from 21 to 42 d of age in wire-floored finishing batteries placed in environmental chambers. The chambers were programmed to provide either a constant thermoneutral temperature (21.1 C), a constant cold temperature (15.5 C), or a cycling hot diurnal temperature (25.5 to 33.3 C). Within each environment there was a factorial arrangement of three Lys levels (1.0, 1.1, and 1.2%) with four Arg:Lys ratios (1.1:1, 1.2:1, 1.3:1, and 1.4:1). Environmental temperature significantly influenced virtually every characteristic examined. Hot cyclic temperatures reduced weight gain, feed intake, and breast meat yield, and increased feed conversion, dressing percentage, leg quarter yield, and abdominal fat content. The cold environment promoted increased feed intake and mortality. Ascites and cardiomyopathy were the leading causes of death under cold exposure and thermoneutral conditions, whereas complications arising from heat exposure were the main cause of death under hot cyclic conditions. Levels of Lys affected leg quarter yield and abdominal fat content over all environments but increased breast meat yield only under cold conditions. Increasing Arg:Lys ratios improved feed conversion and dressing percentage and reduced abdominal fat content; it could not be determined whether these responses were consistent with Arg per se or were due to a nonspecific N response. As increasing Lys levels or Arg:Lys ratios did not improve weight gain, increase breast meat yield, or attenuate adverse effects due to heat or cold exposure, it is concluded that the levels of Lys and Arg suggested for 21 to 42 d by the NRC are adequate for birds of this age under the environmental conditions encountered.