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METABOLISM AND NUTRITION |
* Departamento de Producción Animal, and Departamento de Medicina y Cirugía Animal, Facultad de Veterinaria, Universidad de Murcia, Campus de Espinardo, 30071 Murcia, Spain
1 Corresponding author: pcatala{at}um.es
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Key Words: phytase • phytate • broiler • tibiotarsus mineralization • farm
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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To counteract the antinutritional effects of phytic acid, various alternatives have been proposed (Maenz, 2001), including methods to improve phytate-bound P utilization by broilers (feed supplementation of vitamin D, microbial phytase, or mineral chelators) and methods to reduce the phytate content of feed ingredients. Among these alternatives, one of the most practical and effective methods is the addition of microbial phytase.
Natuphos (EC 3.1.3.8 [EC] , BASF Group, Ludwigshafen, Germany) is a microbial phytase from Aspergillus niger, active within a broad pH range from 2 to 6.5, showing maximum activity at pH of 2.5 and 5.5 (Adeola and Sands, 2003). Although microbial phytase is moderately heat stable, high pelleting temperatures (up to 90°C) reduce A. niger phytase activity (Simons et al., 1990; Wyss et al., 1998). Exposure to 90°C is associated with an irreversible conformational change and with losses in enzymatic activity of 70 to 80%. It is recommended to use Natuphos in a postpelleting liquid application (PPLA) when the pelleting temperature exceeds 85°C to prevent high-temperature denaturation of the phytase enzyme, but accurate temperature trials have shown that A. niger phytase is essentially inactived at 65°C (Berka et al., 1998) or 63.3°C (Lehmann et al., 2000).
It has been reported that phytate hydrolysis is affected by many factors such as dietary Ca, vitamin D3, fiber and Ca:P, type of dietary ingredients, feed processing, age, and genotype of broilers (Lei et al., 1994; Ravindran et al., 1995; Sebastian et al., 1998; Tamim and Angel, 2003; Tamim et al., 2004). Nevertheless, no reports have evaluated the effect of Ca- and P-deficient diets plus phytase on broilers raised under environmental conditions in which movement limitation and access to litter differ. Movement limitation reduce physical activity and could lead to lower bone mineralization (Wilson, 1991; Fanatico et al., 2005). When evaluating bone mineralization, any source of minerals must be controlled, and access to litter could represent an additional mineral supply to feed. Moreover, previous experiments were usually conducted with corn-soybean based diets, and did not continue to market age (42 d). This was partially because endogenous phytase activity from corn is lower than from wheat (Eeckhout and De Paepe, 1994), so the awaited improvement of specific phytase addition to wheat-based diets could be lower. Therefore, the objective of this work was to evaluate, for a wheat–soybean-based diet, the effect of several low levels of Ca and TP diets supplemented with microbial phytase (Natuphos) PPLA on broiler BW and tibiotarsus bone mineralization in different farming conditions (cages, floor pens, and commercial farms) up to 21 and 42 d of age. To characterize mineral metabolism, plasma minerals and alkaline phosphatase (ALP) activity were measured, in addition to mineral excretion in the litter on commercial farms.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Two-phase diets were used: the starter and finisher diets were fed from 1 to 21 d and from 22 to 42 d of age, respectively. The starter feed was offered in crumbles, and the finisher diet was steam-pelleted using a 4-mm die. In each period, 4 treatments were compared (Table 1
): treatment 1 was a control (SC and FC for starter and finisher diets, respectively) containing sufficient TP to cover available P (AP) requirements according to the NRC (1994) and with no specific phytase addition; treatment 2 had low levels of TP [0.61% for starter (SL400) and 0.54% for finisher (FL400) diets] and 400 U/kg of PPLA Natuphos phytase; treatment 3 had the same TP level as treatment 2 but 600 U/kg of the same phytase; treatment 4 had very low TP levels [0.52% for starter (SVL600) and 0.44% for finisher (FVL600) diets] and 600 U/kg of the same phytase. The TP levels used in treatment 4 were the commercially recommended levels for diets containing added phytase. Calcium levels were formulated to reach approximately a 1.2:1 constant Ca:TP.
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Experiment 2
Two hundred forty Ross male 1-d-old broiler chickens were homogeneously distributed by mean weight among sixteen 1 x 1 m floor pens (15 broilers per pen) built in a commercial farm. This provided 4 replicates per treatment in a randomized complete block design. The floor pens had wood shavings for litter, so broilers had access to litter and their mobility was limited. All broilers were weighed individually at d 21 and 42. Broiler density at 21 d was adjusted as in Experiment 1.
Experiment 3
One hundred two thousand Ross broiler chickens of both sexes were placed in 4 commercial farms. Two farms, each containing 21,000 broilers, were assigned to treatments 1 and 2, and the other 2 farms, each containing 30,000 broilers, were assigned to treatments 3 and 4. Each farm had a broiler density similar to Experiments 1 and 2. Broilers had access to litter without mobility restriction. Twenty-five male broilers of each treatment were individually weighed at d 21, as well as 15 male broilers per treatment at d 42. To determine dry litter Ca and P, 2 samples (each corresponding to 20 subsamples taken from 20 places on the farm floor) were taken per treatment group.
Analytical Procedure
Feed samples were ground to pass through a 1-mm sieve and analyzed for N content using the Kjeldahl method (AOAC International, 1990) and CP (N x 6.25). The DM content of the feed was determined in an oven at 103°C for 8 h. Calcium and P were determined by an inductively coupled plasma emission spectrometer (Optima 2000 DV, Perkin-Elmer, Überlingen, Germany). Dietary phytase activity was measured by direct incubation of the samples according to Eeckhout and De Paepe (1994). All values were expressed on a DM basis.
For bone ash percentage determination, 1 bird per replicate in Experiments 1 and 2 and 5 birds per treatment in Experiment 3 were killed by cervical dislocation at 21 and 42 d of age. Later, the right tibiotarsus was removed, boiled, and cleaned from adherent tissue. As described by Brenes et al. (2003), the bones were dried at 110°C for 12 h, defatted with ether for 48 h, dried again at 110°C for 12 h, and finally ashed at 550°C for 12 h in a muffle furnace. The ash content was expressed as a percentage of dry fat-free bone weight. The tibiotarsus, feed, and litter ashes were treated with 6N HCl to determine the Ca and P content by inductively coupled plasma. In Experiment 3, bone Ca and P were only analyzed from 42-d-old birds.
In Experiments 1 and 2, blood samples were obtained by intracardiac puncture at 42 d of age from 1 bird per replicate. Calcium, P, and ALP activity were analyzed from plasma at the Clinical Pathology Laboratory, Universidad de Murcia, Spain, by procedures conventionally used for diagnosing domestic animals (Kaneko, 1989).
Statistical Analysis
The effect of treatment diets on BW, tibiotarsus parameters, plasma minerals, ALP activity, and dry litter Ca and P were analyzed statistically by ANOVA with SPSS Inc. (1997) software. When significant differences were found, the least significant difference test was calculated (Snedecor and Cochran, 1980). All statements of significance are based on a probability of <0.05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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. During the experimental period, no statistical differences were measured in BW; tibiotarsus ash; tibiotarsus ash Ca, P, or Ca:P; and plasma Ca, P, or ALP activity in the broilers fed different treatments.
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. At 21 d of age, the lowest BW and tibiotarsus ash levels were seen in broilers fed SVL600. At 42 d of age, broilers fed FC were numerically lighter than the components of the other groups. No statistical differences in the rest of measured parameters were observed among treatment groups.
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. The highest BW at 21 d of age was shown by the control group. At 42 d of age, the broilers fed the low-TP diet (0.54%) plus phytase (FL400 and FL600) were heavier than the control group (FC) and the very low TP (0.44%) plus phytase group (FVL600). Right tibiotarsus parameters were similar among diets. As regards dry litter Ca and P (Figure 1), the particular diet had a marked effect. Litter of broilers fed the diet with no added phytase (FC) had the highest Ca and P contents, whereas the lowest values corresponded to the diet with the lowest Ca and P content (FVL600) with phytase supplementation.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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At 42 d of age, BW in Experiment 1 was not affected by the treatment diet. Nevertheless, in Experiments 2 and 3, a different tendency from that observed at 21 d was noticed, and in both experiments, the highest BW was observed for birds fed FL400 and FL600. Yan et al. (2000, 2004) and Angel et al. (2005), using corn–soybean-based diets in floor-littered pens, found no differences in BW when comparing 18- to 21-d-old broilers fed the NRC-1994 recommended P level and broilers fed less P but with added phytase.
Body weight was probably not a good indicator of the effects produced by reduced-TP diets plus phytase with respect to a control diet. Indeed, Dhandu and Angel (2003) reported that BW was not a sensitive indicator of mineral sufficiency in broilers.
We also observed that broilers in cages seemed to be heavier than broilers reared on the floor. Different BW lead to different bone mechanical stimulation, probably different bone ash, and perhaps different AP requirements. Reece et al. (1971) reported that male broilers reared in cages were heavier at 8 wk of age than those reared on the floor. This could be explained by the fact that broilers raised using commercial conditions were probably exposed to rearing conditions of harder social and environmental stress that negatively affected performance. In housing conditions of a farm location, broilers could interact with a higher number of broilers, they were directly in contact with litter (consequently having a higher microbial challenge), and floor surface per bird was variable because of flock movements along the farm. Previous studies showed that broilers in the farm did not restrict their movements to small areas in which they could become acquainted with their neighbors (Newberry and Hall, 1990).
Tibiotarsus Bone Mineralization
In chicks, it has been extensively reported that phytase addition to corn–soybean-based diets permits TP levels to be reduced without impairing bone ash (Broz et al., 1994; Qian et al., 1996; Sebastian et al., 1996b; Leeson et al., 2000; Yan et al., 2001; Viveros et al., 2002; Brenes et al., 2003; Dilger et al., 2004; Onyango et al., 2004, 2005; Payne et al., 2005), and only Rama Rao et al. (1999) disagreed. Nevertheless, the level of TP reduction according to broiler age in phytase-supplemented diets lacks consensus.
In our study, differences in tibiotarsus ash among diets at 21 d of age were only observed in Experiment 2, whereas broilers fed diets SC, SL400, and SL600 had higher tibiotarsus ash than broilers fed the SVL600 diet (P < 0.001). Thus, 21-d-old broilers fed 0.28% AP plus 400 or 600 U/kg of phytase were able to mineralize bone similar to the control group, but broilers fed 0.20% AP plus phytase did not. In Experiment 3, the same tendency was observed. It seems, therefore, that the effect of treatment diet on tibiotarsus mineralization at 21 d of age was affected by the environmental conditions of rearing, particularly considering movement restriction and access to litter. In 0- to 3-wk-old chicks, Viveros et al. (2002) found that bone ash was not impaired when phytase was added to a 0.35% AP corn–soybean-based diet, but when a 0.22% AP plus phytase diet was tested, bone ash was lower than the obtained with a control diet.
For chicks from 1 to 21 d of age, the P level in a sorghum–soybean-based diet to maximize tibiotarsus ash needed to be higher than that necessary for BW gain (Beltrán-López et al., 2000). In our trial, 0.52% of TP (SVL600 diet) did not maximize BW or tibiotarsus ash when broilers were raised in pens (Experiment 2) and did not maximize BW in farm conditions (Experiment 3).
In all the experiments, very low Ca and AP levels (0.6 and 0.16%) plus phytase in the finisher period were sufficient to fulfill tibiotarsus ash, Ca, and P requirements to mineralize this bone in the same way as the control diet.
Yan et al. (2004) found that tibiotarsus ash from 42-d-old broilers fed a corn–soybean-based diet containing 0.20% of AP plus phytase did not statistically differ from that obtained with the NRC-(1994) recommended AP level diet (0.35%). In our experiments, the AP level of the FVL600 diet (0.16%) was lower than in the experimental diet reported by Yan et al. (2004), and no impairment of tibiotarsus mineralization was noticed. Nevertheless, when chicks were fed a lower-AP (0.14%) corn–soybean-based diet plus phytase from 3 to 6 wk, Viveros et al. (2002) found that bone ash was impaired compared with the control group. However, previous studies showed that the negative effect on the bone strength of 4- to 6-wk-old chicks fed low-AP (0.22%) corn–soybean-based diets was completely reversed by the inclusion of phytase (Sohail and Roland, 1999).
In our experiments with wheat–soybean-based diets, Ca, P, and Ca:P of the bone ash were not affected by the type of diet. It has been reported that the Ca and P contents in broiler tibiotarsus ash are not influenced by the addition of phytase to low-TP corn–soybean-based diets (Broz et al., 1994; Sebastian et al., 1996a,b; Rama Rao et al., 1999; Viveros et al., 2002) and corn–rice–soybean-based diets (Ahmad et al., 2000) compared with control diets. In contrast, Brenes et al. (2003) found that phytase addition to a low-P corn–soybean-based diet improved Ca and P in the tibiotarsus ash, compared with the same diet without phytase supplementation.
On the other hand, commercial farm-raised broilers, with access to litter and with more space for physical activity than in floor pens and cages, numerically seemed to have a higher tibiotarsus ash content than broilers raised in floor pens and cages. More exercise may lead to stronger bones (Fanatico et al., 2005), and bone strength is related to bone ash content (Wilson, 1991). Wabeck and Littlefield (1972) reported that the tibiotarsus breaking strength of broilers reared in cages was lower than in broilers reared in floor pens. Changes in the rate of bone resorption or deposition can be brought about by mechanical stimulation (Antalíková et al., 2001). Previous studies in hens showed that animals housed in floor pens had higher bone ash levels than animals maintained in cages (Rowland et al., 1968; Rowland and Harms, 1970; Meyer and Sunde, 1974) but not in broilers (Bond et al., 1991).
Therefore, the effect of low-TP wheat–soybean-based diets plus phytase on tibiotarsus mineralization was affected by environmental conditions, meaning that the results of trials carried out in cages (current experimental conditions) are not applicable to commercial farm housing conditions.
Mineral Metabolism
No statistical differences among treatments appeared in the plasma Ca and P contents of 42-d-old broilers. Plasma levels of P are a result of the homeostatic regulation of P, and significant lowering of these levels may be indicative of low body P reserves (Onyango et al., 2004), which seemed not to be the case for broilers fed the FL400, FL600, and FVL600 diets. Phytate-bound P liberated by phytase is available in the gut to be absorbed to maintain normal P homeostasis, and this seemed to be the case for broilers fed the FL400, FL600, and FVL600 diets.
Previously published results related to the effect of low-Ca and P diets with phytase supplementation on Ca and P plasma levels varied. Onyango et al. (2004) reported that feeding chicks with low-Ca and P corn–soybean-based diets with or without phytase did not modify broiler serum Ca levels, but only phytase-supplemented P-deficient diets improved serum P levels to the same extent as adequate P diets alone. Viveros et al. (2002), Broz et al. (1994), Sebastian et al. (1996a, b), and Juanpere et al. (2004) found that phytase addition to low-P corn–soybean and barley–soybean-based diets significantly increased plasma P but reduced plasma Ca in chicks. Keshavarz (2000) did not find any significant improvement in plasma P as a result of phytase addition to low-P corn–oat–soybean-based diets in 6-, 12-, or 18-wk-old pullets.
The diet had no statistical effect on the ALP activity. Increased ALP activity in plasma is associated with increased osteoblastic activity in bone (Moss, 1982), which is greater in disorders in which growth or remodeling of bone is taking place (Brenes et al., 2003) and is probably related to Ca or P deficiency (Rama Rao et al., 2003; Lan-xia et al., 2006). In previous studies, Huff et al. (1998) reported a decrease in ALP activity when phytase was added to P-deficient corn–soybean-based diets, probably related to the downregulation of this enzyme resulting from the increased availability of P. However, Roberson and Edwards (1994) reported that phytase addition to low-Ca and high-P corn–soybean-based diet did not influence ALP activity.
P Excretion in Farm
Calcium and P were measured in the 42-d-old broiler litter in Experiment 3. The 17.8, 17.8, and 33.4% reduction in Ca level in FL400, FL600, and FVL600 diets, respectively, compared with FC diet was reflected in the corresponding reductions observed in the Ca level of the dry litter (–19.6, –18.7 and –38.7%, respectively).
At the same time, P reduction in FL400, FL600, and FVL600 diets formulation was –25.7, –25.7, and –38.9%, respectively, compared with the FC diet. The P reduction of dry litter from broilers fed the FL400, FL600, and FVL600 diets (with phytase addition) was –35.2, –32.1, and –54.1%, respectively, compared with dry litter from broilers fed the FC diet (control diet). In this case, it seemed that phytase addition contributed highly to litter P reduction. Lower nonphytate P and phytase diet supplementation could be effective in reducing litter P (Maguire et al., 2004; McGrath et al., 2005).
In conclusion, the response of broilers to the experimental diets differed according to bird housing, concretely when movement limitation and access to litter differed. The very low-Ca and TP wheat–soybean-based diet plus phytase did not impair broiler BW, tibiotarsus mineralization, or mineral metabolism up to 21 or 42 d of age under highly controlled hygienic environmental conditions (Experiment 1). When broilers were reared in floor pens on a farm, the same diet reduced BW and tibiotarsus ash at 21 d of age but not at 42 d of age (Experiment 2). In commercial farms (Experiment 3), all the diets led to a similar tibiotarsus ash content, but broilers fed low TP plus phytase (400 or 600 U/kg) were the heaviest at 42 d of age. In addition, P excretion to the litter was reduced by 35.2 and 32.1% with the low-TP plus phytase diets and by 54.1% with the very low-TP plus phytase diet.
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ACKNOWLEDGMENTS |
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Received for publication March 7, 2006. Accepted for publication July 4, 2006.
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