THE EFFECT OF CALCIUM AND MAGNESIUM SUPPLEMENTATION ON PERFORMANCE AND BONE STRENGTH OF BROILER CHICKENS

Aim of the experiment was evaluation of the effect of reduced calcium and magnesium content in the broiler chickens diet on its parameters of fattening, bone strength and calcium and magnesium content in liver. The trial was performed with cockerels of Ross 308 hybrid (n = 160) which were fattened in cage batteries from day 11 to 36 day of age. Cockerels were divided into 4 groups (differ in various intake levels of calcium and magnesium) in four replications. The maizewheat-soybean basal diet contained 2.33 g Ca and 1.58 g Mg per kilogram. Calcium was added by CaCO3 and magnesium by MgSO4. Control group (C) received feed mixture with added CaCO3 in dose of 19.49 g.kg -1 and 0.41 g.kg of MgSO4. Three experimental groups contain added CaCO3 in dose of 11.83 g.kg -1 and 0 g.kg MgSO4 (group Exp1); CaCO3 11.83 g.kg -1 and 0.41 g.kg MgSO4 (group Exp2); CaCO3 19.49 g.kg -1 and 0 g.kg MgSO4 (group Exp3), respectively. The feed consumption was daily monitored and the cockerels were weighed twice a week. At the end of the study the experimental animals were weighted and slaughtered by decapitation. The weight of carcasses, liver and proportion of breast and thigh muscle was determined in the selected chickens (n = 24). The atomic absorption spectrometry was used for Ca and Mg evaluation in liver tissues. Bone strength parameter was measured at the femur bone. The statistically significant differences (p >0.05) were not detected between control and experimental groups in the case of studied parameters of fattening, bone strength and calcium and magnesium content in the chicken ́s liver. Based on the obtained results it could be concluded the reduction of determined elements in the chicken diet did not deteriorate parameters of yield, elements content in liver tissue as well as the bone strength of broiler chickens.


INTRODUCTION
Calcium (Ca) has important biological functions and must be provided in adequate amounts (Peters and Mahan 2008).Inadequate calcium intake may affect bone mineral content, muscle function and other functions of minerals in the body (Peters and Mahan 2008;Horky, 2015).Unfortunately, the mineral requirements of broiler chickens, as determined by several organizations 10 -20 years ago, may not support optimal chicken performance in today's strain (Ruttanavut and Yamauchi 2010).It is known that the genetic makeup of the bird influences the utilization of Ca and thereby its requirement.Therefore, it is presumed that the requirement of Ca may not be the same as reported in earlier studies to meet the demand for highly productive birds (Shafey et al., 1990; Hurwitz et al., 1995).Magnesium (Mg)  indicates the delivered amount of calcium and magnesium in feed mixtures for fattening chickens 9 g.kg -1 of calcium and 0.5 g.kg -1 of magnesium.Magnesium is one of the most abundant divalent cation in living cells and plays a vital role in many cellular processes.Magnesium deficiency or reduction in dietary intake of Mg 2+ is strongly correlated with numerous metabolic abnormalities and chronic diseases including diabetes, ischemic heart disease and hypertension in which the accumulation of reactive oxygen species (ROS) is commonly observed  2. The crumbly feed mixture was supplied ad-libitum and its consumption was recorded every day.Access to drinking water was also ad-libitum.Weighing of chickens was carried two times a week.Microclimate and lighting regime were modified according to the technological instructions for Ross 308.The values of microclimate were recorded every day.

Evaluating of carcass quality
The experimental animals were weighted and slaughtered by decapitation in the age of 36 days.The weight of selected carcases (n = 24) was determined.The carcase was free of neck, feather, offal and feet.After liver dissection, the livers were weighted and the percentage of the live weight of chicken was calculated.Subsequently, the skin from breast was removed and breast meat was deboned.The skin from legs was also removed and the legs were deboned.After breast and legs dissection, the muscles were weighted and the percentage of the live weight of chicken was calculated.

Bone strength measurement
For the measurement was used a universal apparatus for measuring physical characteristics -TIRATEST 27025 (Germany).The device allows measurements of different materials in tension, compressive and flexural strength.To test the strength of bone was chosen three-point bending.Loading speed was 100 mm / min until fracture of bone.Bone strength parameter was measured at the femur bone.

Statistical analysis
Data has been processed by Microsoft Excel (USA) and STATISTICA.CZ, version 12.0 (CZ).The results were expressed as mean ± standard deviation.One-way analysis (ANOVA) was used.Sheffe´s test was applied to defined statistical differences and the differences between groups were considered significant at p <0.05.

RESULTS AND DISCUSSION
During the experiment, the highest average feed consumption 4.65 kg per chicken was estimated in the group Exp2 (Table 3).The lowest feed consumption was estimated in the control group (4.47 kg per chicken.The differences of the feed consumption between both groups were not statistically significant (p >0.05).The determined feed consumption is lower than Akter et al described (Akter et al. 2016).It could be concluded the change of Ca and Mg content in the feed mixture did not affect the feed consumption significantly.This result is in agreement with Akter et al. ( 2016) who described the influence of low content of Ca in feed mixture which affects the increase intake of feed mixture by broiler chickens.
At the end of trial was observed non-significant (p >0.05) higher average weight of chickens (2 126 g) in Exp2 group (Table 4) 2013).However, we did not notice the described trend in our experiment.Whereas Liu et al. ( 2007) found the addition of magnesium to the feed mixture did not influence the average liveweight and feed intake in chickens.
Table 5 present the carcass yield.The highest carcass yield was found in the Exp1 group (73.62%) but differences between groups were not significant (p >0.05).Carcass yield, stated in the technological procedure for Ross 308 (Aviagen Group 2014), is the 71.72% for 2,000 g of live weight.The higher breast and leg meat yield was found in the Exp1group.According to the manual of hybrid Ross 308 (Aviagen Group 2014) 21.20% of breast muscle at 2,000 g of live weight is stated.The same manual (Aviagen Group 2014) indicates a yield of leg meat 16.01% for 2,000 g live weight.The differences among groups in slaughtering yields were not statistically significant (p >0.05).Our results are in a good agreement with Akter et al. ( 2016), who found the different amount of calcium in the feed mixture did not affect of the carcase yield and the proportion of breast and thigh muscle in tested chickens.On the contrary of Salmanzadeh et al. (2012) observed in their experiment that glucose and glucose + magnesium administration significantly increased the breast muscle size of broiler chickens.
The highest liver weight was found in the control group compared to experimental groups (Table 5).Values are not statistically significant (p >0.05).Similar results were published by Štenclová et al. (2016).They determined the low amount of zinc in the feed mixture significantly affect  the higher weight of liver in the control group in comparison with experimental group of chickens.
Table 6 shows average concentration of Ca and Mg in the liver (mg.kg -1 fresh weight).The highest content of calcium in liver was estimated in the control group of chickens.The experimental group Exp2 showed the highest content of magnesium.The differences among analyzed groups were not statistically significant (p >0.05).Our obtained results of Ca and Mg content in the liver tissue of broilers are comparable with results published by Majewska et al. (2016).They observed the low calcium concentration (70.76 mg.kg -1 ) and higher magnesium concentration (328.62 mg.kg -1 ) in liver tissue of broiler chickens.
The highest average of leg bone strength was reached in the experimental group Exp2 (Table 7).However, the differences among examined groups were not statistically significant (p >0.05).Askari et al (2015) found the average leg bone strength 246 N/m 2 , that responds to our results of control group.The leg bone strength was determined 221.82 N/m 2 in the case of group with reduced content of Ca-P in the feed mixture.In contrary to results obtained by Swiątkiewicz et al. (2011) the decreased level of calcium and phosphorus was tended to reduce breaking point of leg bone of broiler chicken.

CONCLUSION
From the obtained results is evident the reduced supplementation of calcium and selenium did not influence the evaluated parameters of fattened chickens.Based on our results could be concluded the reduced content of studied elements did not cause the reduction of feed intake, neither the parameters of fattening and bone strength.Prior to eventual introduction of low calcium and magnesium diet for fattened chicken is essential to carry out further studies for evaluation of possible interactions with other mineral elements.
metabolism is closely associated with Ca and phosphorus (McDonald et al., 2011; Horky et al. 2016).Yang et al. (2012) reported that dietary MgSO 4 supplementation significantly prevented heat stress-induced oxidative damage and improved growth performance in broilers.Some minerals such as zinc (Zn), and Mg are strongly associated with the antioxidant defense of organism (Sahin et al., 2006).Recommended nutrient content by Zelenka et al. (2007) . Whereas Hoeven-Hangoor et al. (2013) presented the addition of 0.255 g.kg -1 MgSO4 was affected the average liveweight of chickens 2355g on 36th day of life.Akter et al. (2016) showed the addition 10 g.kg -1 of calcium in comparison with v 6 g.kg -1 in the feed mixture highly influenced the decrease of liveweight gain.Similar results were published by Rama Rao et al. (2006) and Singh et al. (

(Chakraborti et al., 2002; Guerrero-Romero and Rodriguez-Moran, 2002; Song et al., 2005; Valko et al., 2007; Bo and Pisu, 2008; Nevrkla et al., 2014; Nevrkla et al., 2016, Horky, 2014; Horky et al. 2012).
Aim of the experiment was evaluation of the effect of reduced calcium and magnesium content in the diet of broiler chicken on parameters of fattening, bone strength and calcium and magnesium content in the chicken´s liver.

Table 1
Composition of the basal diet.

Table 2
Addition of CaCO 3 and MgSO 4 (g.kg - ) and total levels of Ca and Mg (g.kg -1 ) in the diet.

Table 3
Feed consumption per chicken and trial.

Table 4
The average weight of broiler chickens at the beginning and end of the experiment.

Table 5
Carcass yield.Differences between groups were not statistically significant (p >0.05).

Table 6
Concentration of Ca and Mg in the liver (mg.kg -1 fresh weight).Differences between groups were not statistically significant (p >0.05).

Table 7
Bone strength.Differences between groups were not statistically significant (p >0.05).