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ENVIRONMENT, WELL-BEING, AND BEHAVIOR |



* Department of Poultry Science, College of Agriculture and Life Sciences, North Carolina State University, Raleigh 27695-7608;
Grupo Grica, Faculty of Agriculture, University of Antioquia, Medellin, Colombia;
Department of Crop and Soil Environmental Sciences, Virginia Tech, Blacksburg 24061; and
Escuela Agrìcola Panamericana, Zamorano, Center for Poultry Research and Teaching, Tegucigalpa, Honduras
2 Corresponding author: jbrake{at}ncsu.edu
| ABSTRACT |
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Key Words: broiler breeder phosphorus phytase environment litter
| INTRODUCTION |
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| MATERIALS AND METHODS |
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Pullet and Breeder Management
A total of 1,088 1-d-old Ross 308 breeder pullets and 200 one-day-old Ross 344 cockerels were placed in a blackout growing house and reared sex-separate, with either 68 female or 50 male chicks randomly assigned to each of 16 female or 4 male pens of 3.96 x 3.96 m. The lighting program consisted of 23 h of light per day for 1 wk, followed by 8L:16D to 21 wk of age. The management and house infrastructure were as generally described by Brake and Baughman (1989). At 21 wk, 60 pullets from each of the 16 female rearing pens as well as 6 cockerels from the pens of males on the same treatment were moved to each of 16 breeder pens located within a curtain-sided breeder house. The laying pen dimensions were similar to those of the growing house, whereas two-thirds of each breeder pen was covered with raised plastic slats and a scratch area with fresh pine shavings constituted the remaining one-third of each pen. Each pen contained one automatic waterer, one 12-hole galvanized nest box, 5 tube feeders with male exclusion grills for females that were located above the slats, and one tube feeder for males, located over the scratch area. At 20 and 22 wk, the photoperiod was increased to 14 and 15 h, respectively, after which it was further increased to 15.5 h at 5% lay and again to 16 h at 50% lay. All eggs laid were collected twice daily and stored at 18.6°C and 70% RH until incubated in Jamesway 252B incubators (Jamesway Incubator Company, Ft. Atkinson, WI). The fertility of eggs was determined from sets of 60 eggs per pen, which were incubated biweekly from 28 to 64 wk of age. The treatment identity of hatching eggs was maintained by breeder pen throughout the incubation and hatching process. After 21.5 d of incubation, all eggs that did not hatch were broken out and examined macroscopically, and the percentage of fertility and stage of embryonic mortality were calculated. All eggs that were accidentally cracked were deleted from the analyses.
Pullet and Breeder Diets
From placement to 3 wk of age, all chicks received a common pullet starter diet (2,925 kcal/kg of ME and 17.66% CP), followed by a common grower diet (2,925 kcal/kg of ME and 15.96% CP) to 9 wk of age (Table 1
). From 10 wk of age, 4 female pens and 1 male pen were randomly assigned to 1 of 4 treatment groups (A, B, C, D) that received diets with different combinations of AvP or NPP in the presence or absence of a fungal-derived phytase (Allzyme SSF; Alltech Inc., Nicholasville, KY) during the growing (10 to 21 wk) and laying period (22 to 64 wk; Table 2
). For the grower period, diets fed to treatment A contained 0.37% NPP with no added phytase. Treatment B contained 0.27% NPP with 300 FTU of phytase. Treatment C contained 0.27% NPP but with no added phytase. The reductions in NPP between treatments A and B were based on the recommendation of the phytase manufacturer that the addition of 300 FTU of phytase in pullet-rearing diets was able to replace the equivalent of 0.10% NPP from dicalcium phosphate. In a similar manner, the NPP level of the grower diet fed to treatment D was reduced by 0.10% from that in treatment C (to 0.17%) while simultaneously adding 300 FTU of phytase. Further, to reduce the phytase contribution from endogenous sources, the wheat bran and a portion of the corn, poultry fat, and vermiculite was removed from the diet formulation and pelleted separately as a premix, which consisted of 37% corn, 58% wheat bran, 1.6% poultry fat, and 3.4% vermiculite. The reduction in basal phytase activity of the pelleted bran premix was confirmed prior to mixing it back into the diets at levels that reflected the original ingredient quantities in each formulation. The treatment identity of pens was maintained during transfer from the rearing facility to the production facility. During the 42-wk breeder phase, the NPP level of treatment A was 0.37% with no added phytase, whereas treatment B contained 0.27% NPP and 500 FTU of added phytase. The NPP level of treatment C was further reduced to 0.19% with no added phytase. Breeder treatment D, with 0.09% NPP, was created by removing all remaining dicalcium phosphate from the breeder diets fed to treatment C while adding 500 FTU of phytase. The phytase included in breeder diets B and D was increased to 500 FTU/kg during the breeder layer phase to increase the likelihood of detecting potentially deleterious effects of phytase on the performance of the broiler breeder progeny, as had been reported previously (Brake et al., 2003).
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Statistical Methods
A pen of birds was the experimental unit for all live production measurements. Egg production, fertility, and hatchability data were analyzed on a cumulative basis from 29 to 64 wk. Litter data from the rearing phase were subjected to one-way ANOVA using a completely randomized design with 5 replicate pens per treatment. Upon initial analysis of the data, a significant correlation was found between litter moisture and litter WSP (r = 0.74, P
0.001). To account for this correlation, the percentage of litter moisture was log transformed and then included as a covariate in the subsequent statistical analyses to assess treatment effects on WSP and the ratio of WSP:total P in the rearing litter. Manure samples from breeder pens were analyzed using a split-plot design, with treatment as the main plot and sample area within each pen as the subplot. Because pen was the experimental unit, within-pen variation in the manure analyses was not considered in the estimation of treatment effects during the breeder phase, and spatial effects within individual pens were reported previously by Maguire et al. (2006). The GLM procedure of SAS (SAS Institute, 1996) was used to analyze the continuous variables of the broiler breeder production data. Fertility data were analyzed as categorical data, where each individual egg was taken as a binomial event, either fertile or infertile, using the generalized model (GENMOD) procedure of SAS (SAS Institute, 1996). The results of the rearing litter and breeder manure analyses were interpreted using the MIXED procedure of SAS (SAS Institute, 1996). Means were partitioned using protected LSMEANS, and statements of statistical significance were based on P
0.05 unless otherwise stated.
| RESULTS |
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0.001), whereas the moisture level in the litter showed no correlation with the litter total P concentration (Table 3
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| DISCUSSION |
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In a similar manner, reductions in the dietary NPP with or without phytase did not affect the proportion of WSP in manure produced from 22 to 64 wk of age. The concentrations of total P and WSP in the breeder manure again reflected the positive benefits that could be obtained by decreasing dietary NPP levels, either alone or in combination with dietary phytase enzymes, and showed a potential reduction in total P of 39 or 42% when NPP was reduced from 0.37% to either 0.19 or 0.09% without or with phytase, respectively (Table 4
). Although the reduction in NPP from 0.19 to 0.09% while adding phytase provided no additional benefits in further reducing the manure total P, this did allow for the complete removal of all added inorganic phosphate from the diet while also having a positive effect on the percentage of hen-day egg production. Li et al. (2002) previously reported an increased egg production of 0.55% from 26 to 40 wk of age and a 2% improvement in hatchability when NPP was reduced from 0.30 to 0.10% and phytase was added to the diets of broiler breeders housed in slat-litter pens. However, because there were only 2 dietary treatments in their study, it was not possible to differentiate between the effects of NPP and phytase. In contrast to the positive effect on egg production that was shown in our study and in the study by Li et al. (2002), Brake et al. (2003) were unable to find any change in broiler breeder performance when all added inorganic P was replaced by phytase in 2 previous studies. The reduction in fertility that occurred in our study when dietary NPP was reduced below 0.37% has not been previously reported in broiler breeders. The effect of NPP level on fertility in our study might have been related to the early start (10 wk of age) of the reduced NPP treatments and warrants further study. Nevertheless, in spite of the potentially detrimental effect on fertility, the slightly higher egg production of treatments that had received less than 0.37% NPP, although not statistically significant, contributed to there being no treatment differences in the number of chicks produced per hen.
Our calculations showed that a broiler breeder hen housed to 64 wk of age consumed 397 g of total dietary P, of which approximately 41%, or 165 g/bird, was excreted in the litter and manure produced (Plumstead et al., 2005). Data from the present study suggest that the replacement of 0.10% dietary NPP with phytase had little effect on reducing the total litter P in diets fed to pullets that had been reared on litter. However, once transferred to a two-thirds slat-litter breeder house, the replacement of all added inorganic P in the diets fed to broiler breeders with 500 FTU of phytase could provide substantial benefits to producers by reducing the concentrations of P in manure from broiler breeders by as much as 42% without affecting the number of chicks produced per breeder hen housed.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Received for publication June 20, 2006. Accepted for publication October 13, 2006.
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