THE RETENTION OF MINERAL SUBSTANCES, QUALITY AND CHEMICAL COMPOSITION OF BONES OF CHICKENS FED DIETS CONTAINING DIFFERENT CALCIUM AND PHOSPHORUS LEVELS

Dorota Jamroz¹, Tomasz Wertelecki², Romuald Żyłka^3
1 Department of Animal Nutrition and Feed Management, Wrocław University of Environmental and Life Sciences, Wrocław, Poland
² Department of Animal Nutrition and Feed Science, Wrocław University of Environmental and Life Sciences, Poland
³ Department of Biophysics, Wrocław University of Environmental and Life Sciences, Poland

ABSTRACT

Lowered calcium concentration in feed mixture from 11.0 to 9.1 g kg^-1 and phosphorus content from 7.0 to 6.0 g kg^-1 has decreased the body weight in 28 day of life, as well as Ca and Cu accretion in organism, however the phosphorus, magnesium and manganese retention was better in group fed diet with lower Ca/P content. Better bone mechanical quality parameters and higher Ca amounts in bones were obtained in chicken fed diets containing a higher Ca and P amounts in the diets; in the P, Mg, Mn, Cu, Zn content in bone ash only small variations were observed.

Key words: bones, broilers, mineral composition.

INTRODUCTION

The international recommendations of optimum phosphorus level in broiler diets are very diversified and depends on many factors, such as feeding system, age of chickens, genotype of birds, sources of P, kind of compounds used in mixtures (NSP content) and supplementation with feed enzymes (phytase) [2, 4, 5, 9, 10, 13, 16, 17, 20, 21, 23, 30]. According to the different recommendations for example by Food and Nutrition Board – recommended dietary allowances (1984) [12], National Research Council – Nutrient Requirements of Poultry (1994) [28] and Environmental Protection Agency (2003) [11] the starter diet for broilers should contain 0.65-0.78% of total phosphorus, in grower and finisher diets the P- quantity vary at limits of 0.6-0.7 and 0.57-0.67%, respectively. The Polish recommendations [29] gives the values approximate to the presented data: total P 0.68-0.64 and P available 0.45-0.38%. The amount of calcium recommended in Polish norms vary at limits of 0.97-0.85% [29]. Recommendations concerning the management of different hybrids give other values of Ca and P requirement, i.e. Hubbard [15] provides the amounts of 11.0 g Ca per kg and 4.7 g P available per kg of diet in first weeks post hatch. The purpose of presented study was to determine the birds’ response to the two Ca and P levels in diets and their effects on the retention of mineral elements as well as both bone quality and their chemical composition.

MATERIAL AND METHODS

Animals and feeding
The experiment was carried out with 100 Hubbard F15 male broiler chickens with average initial body weight 47.4 g, kept in battery cages. One-day old birds were randomly divided into two groups (each 50 birds), each consist of 5 replications (cages) with 10 birds per one. The temperature inside room was gradually reduced from initial 32°C to the 22°C in second phase of rearing. The lighting lasted 24 hrs per day for whole experiment. The birds had free access to drinking water (nipple system).

Chickens were fed with mash mixtures (starter 1-14 and grower 15-28 days) characterized by 215/195 g kg^-1 of protein content and energy density (AME_N) of 12.5 and 12.7 MJ kg^-1, respectively (Table 1). Mixtures were diversified in calcium and phosphorus level: group I fed mixture composed according to the Hubbard Recommendations [15] (Ca – 11.0 g kg^-1 and 4.70 g kg^-1 P available) while group II was fed with mixture containing 9.10 g kg^-1 Ca and 3.80 P available [29]. In mixtures the Ca : P avail. ratio was 2.34-2.46 : 1. Mixtures were given to the chickens ad libitum.

The analysis of nutrients content in compounds and in mixtures were made according to AOAC (2000) [1] standards; amino acids were determined in compounds then calculated in the mixtures.

Bone quality evaluation
On the 1, 7, 14, 21 and 28 day of birds life 10 chickens (two chickens from each cages-replication) (selection criteria – the mean weight in the group) from each group were slaughtered then the right legs were prepared. From the raw material the muscles were removed then the bones (tibia and femur) were cleaned and stored for estimation of quality parameters (10 tibia and 10 femur bones per group). In fresh bones the mechanical parameters, such as strength in maximal force, elasticity, deflection, percentage of break deflection, vector quantity of deflection and breaking structure were determined using the INSTRON apparatus.

The bone deflection (h) was measured by a standard method, in which the force (F) was applied to the shaft of the bone supported on both epiphyses, at L = 13 mm distance for each estimation (Fig. 1). The advance value of head during breaking force estimation on INSTRON apparatus was about 0.5 mm min^-1 for bones from 1 and 2 week-old chickens and 0.8 mm min^-1 for bones of 3 to 4 weeks-old chickens. Force F was changed up to the bone breaking point. The elasticity coefficient αn = F/h was calculated, too. On the basis of the obtained data of the mechanical test, also the maximal loading force Fn (strength at breaking point), maximal bone deflection hn (deflection at breaking point), maximal percent bone deflection Un = hn / L were calculated [17].

After estimation of the mechanical parameters the bones were defatted in ether extract during 24 hours (using Soxhlet method) [1], dried in maximal temperature as 50°C and the allometrical parameters of bones, such as length and weight were analysed. In both bones (tibia and femur) the chemical composition: content of dry matter, crude ash, Ca, P, Mg, Mn, Cu, Zn were also determined according to AOAC standards (2000) [1].

Balance trial – retention of minerals
In days 9-12 (4th days) (starter period with 30 animals per group) and 24-27 (4th days) (grower period with 10 animals per group) of chickens life the balances of calcium, phosphorus, magnesium, manganese, zinc and cupper were performed. The excrements were collected during the period of four days, in them the feed intake and both quantity and chemical composition of excrements were recorded.

All obtained experimental data were evaluated statistically by one factorial ANOVA using SAS® procedures [33]. The factor – age of chickens – was used for determination of the changes of dynamic of analysed parameters, only. Differences between treatment means were tested according to Duncan’s multiple range test [8].

RESULTS AND DISCUSSION

The growth of chickens in both groups during first 3 weeks of life was correctly and similar; on day 28 significantly (P<0.05) higher body weight of remaining 20 birds per group – treatment was noted in group I fed mixture consistent with Hubbard recommendations (Fig. 2).

Reduction of Ca and P content in mixtures given to the birds in period from 9 to 12 day of life unsignificantly (about 2.5 g) has decreased feed intake and significantly retention of calcium (P<0.05) and cuprum (P<0.01), however by lower feed and significantly phosphorus intake and their retention was distinctly higher in group II (P<0.01) as compared to group I. In Zn, and especially Mn retention, relatively great differences between groups were not confirmed statistically (Table 2). In older birds (24-27 days of life) better retention of calcium, phosphorus (P<0.05), Mg and Mn and lowered Cu conversion was stated in group II.

In both balance periods better retention of phosphorus (P<0.05 and 0.01) was stated in birds fed diets with lower Ca and P level, better (P<0.05 or insignificant) Mg and Mn retention (insignificant) were determined in chickens from group II, too. The reverse effects in Zn utilization were observed in first balance periods.

Statistically significant differences between groups were noted only for tibia weight in chickens on 21 day of life (P<0.05) when the better result was obtained for group I. The lengths of tibia and femur measured on 7. day of life were greater in group I. Higher values of this parameter in group I were also stated on day 14, 21 and 28 (P<0.05) (Fig. 3 and 4).

In mechanical parameters the clear tendency to lowering of the strength in maximal force (P<0.05 or insignificant), vector of elasticity, maximal bone deflection and breaking work was determined in femur of chickens from group II. Similar effects of diets with low Ca/P level were noted in decrease of strength (P<0.05) and breaking work of tibia bone of chickens from group II (Table 3).

Diversification of Ca and P level in mixtures (11g Ca; 4.7g P available kg^-1 (I) and 9.1 Ca; 3.8 P available kg^-1 (II) significantly (P<0.05 or 0.01) decreased the crude ash content in tibia and femur and calcium level in tibia (P<0.05) and femur ash (insignificant). In P, Mg, Mn, Zn, Cu content in bone’ ash insignificant differences were stated in both bones (Table 4) and in the composition of bone ash no negative effects of lowered Ca/P content in given mixtures were observed.

Obtained results indicate that in the optimalisation of the Ca and P level in the diets not only age of birds but also other important factor – kind of hybrid and its specific requirement for mineral elements necessary for growth - should be taken into considerations. The universal recommendations, which are published in Polish recommendations, were not enough for Hubbard broiler chickens. Similar dependence was observed in other research by different authors [2, 19, 20, 21, 24, 26].

Lower Ca and P level (from 11 to 9.1 g kg^-1 and from 7.0 to 6.0 g kg^-1, respectively) in presented experiment has decreased the body weight in 28 day of life and reduced the feed intake at the period of 9-12 days of life as well as Ca and Cu accretion, however the phosphorus, magnesium and manganese retention was better in group fed diet with lower Ca/P level.

Better bone mechanical quality parameters and higher Ca amounts were obtained in chicken fed diets containing a higher Ca and P amounts; in the P, Mg, Mn, Cu, Zn in bone ash content only small variations were observed. From the investigations of numerous authors [6, 7, 19, 22, 24, 26, 27, 31, 32, 34] resulted clearly that mineralisation processes are more complicated and diversified or lowered content of substantial mineral ingredients not always directly lead to significant decrease of strength parameters of bones [3, 5, 13, 14, 16, 23, 25, 35]. This problem is the subject of ours further investigations.

CONCLUSION

Better parameters of bone mechanical quality were obtained in chickens fed diets containing highter amount of both ca (11 g kg^-1) and P total (9.1 g kg^-1) in comparison to other groups. In the content of P, Mg, Mn, Cu, Zn in bone ash small variations were stated.

ACKNOWLEDGMENTS

Project supported by University of Environmental and Life Sciences in Wrocław, No. 114/GW/2004.

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Accepted for print: 29.06.2007

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