Specific Appetite for Calcium in Broilers

Summary

A total of 144 Cobb 500 broilers were used to investigate if modern broilers can regulate calcium intake using choice feeding. Birds were fed diets containing 0.25, 0.50, 0.75 or 1.00% total Ca and a separate Ca source (CaCO₃) from 1-21d. Consumption of the separate Ca source increased with decreasing Ca concentration of the mixed ration (P < 0.0001) indicating that modern broilers retain a Ca-specific appetite. Further, weight gain and FCR was inferior in the diets with the highest Ca concentration and this is interpreted as a Cainduced reduction in phytate-P utilisation.

I. INTRODUCTION

Phosphorus (P) in plants and seeds is stored as phytate (myo-inositol hexaphosphate) which is poorly available to monogastric animals (Tamim and Angel, 2003), mainly due to the simultaneous supply of calcium (Ca) as part of the mixed ration. Phytate has 12 reactive sites which range from being strongly acidic (pK 1.5-2.0) to weakly acidic (pK 9.0-11.0) and in the digestive tract of poultry, phytate carries a strong negative charge that is capable of binding di- and trivalent cations such as Zn²⁺, Cu²⁺, Ni²⁺, Co²⁺, Mn²⁺, Fe²⁺and Ca²⁺(Angel et al., 2002). Despite Ca having one of the lowest affinities for phytate, due to its high concentration in poultry diets Ca potentially has the greatest effect. Excess dietary Ca has been reported to impede the availability of other minerals such as P, Mg, Mn, Zn as well as reduce the efficacy of phytase through the formation of Ca-phytate complexes. (Driver et al., 2005; Selle et al., 2009). Reducing the concentration of dietary Ca has been reported to improve phytate-P availability, but this has also been shown to reduce skeletal integrity and have implications for the health and welfare of poultry.

Poultry have been shown to possess specific appetites for nutrients and are able to select a diet from a variety of sources to meet their nutritional requirements. Seminal work in layer hens by Kempster (1916) and Rugg (1925) showed that hens produced more eggs when they were able to choice feed when compared to those fed a single mixed ration. Specific appetites in poultry have also been shown for lysine (Newman and Sands, 1983), methionine (Steinruck et al., 1990), total protein (Forbes and Shariatmadari, 1994), selenium (Zuberbuehler et al., 2002) and Ca (Wood-Gush and Kare, 1966; Hughes and Wood-Gush, 1971; Joshua and Mueller, 1979). Of the available literature, work assessing the Ca specific appetite in poultry predominantly evaluates the consumption of a separate Ca source when fed in combination with either a Ca deficient diet or Ca adequate diet. Few reports detail the response to multiple basal diets formulated with different Ca concentrations in the one experiment. Furthermore, the majority of work using Ca choice feeding models describes work in layer hens. Therefore, the study reported herein investigated whether a modern commercial broiler still possesses a Ca specific appetite as well as the ability to consume sufficient Ca to meet its requirement. The effect of this complementary feeding approach on the digestibility of P and other minerals was also assessed.

A total of 144 Cobb 500 day-old male broilers were obtained from a commercial hatchery, weighed and randomly allocated to one of four dietary treatments in a completely randomised design. Each treatment was replicated six times with six chicks per replicate cage. Broilers were kept at a temperature of 31 °C for days 1-4 and thereafter this was reduced by 0.5 °C/day to 24 °C. The lighting regime for the study consisted of 23L:1D for the first 4 days and then 18L:6D for the remainder of the experiment. Diets were based on maize and soybean meal and consisted of 0.25, 0.50, 0.75 and 1.00% total calcium (Table 1). Available P was formulated at 0.25% in order to assess the effect of Ca feeding strategy on phytate-P digestibility. Maize/soy diets were chosen intentionally to minimise possible confounding effects of endogenous phytase e.g. from wheat. All birds had free access to the mixed ration, a separate source of calcium (CaCO₃ grit, 38% Ca and 2mm mean particle size) and water.

Feed and calcium source intake were recorded daily and body weight weekly. Apparent ileal digestibility (AID) coefficients for crude protein (CP) and minerals were calculated using acid insoluble ash as an indigestible marker. On day 22, all birds were euthanised and ileal contents collected and pooled for each cage. Toe ash measurements were recorded from samples that were obtained by severing the middle toe through the joint between the 2nd and 3rd tarsal bones from the distal end. Toes were collected from individual birds and pooled by treatment replicate. Samples were dried to a constant weight at 105 °C and then ashed in a muffle furnace at 500 °C for 12 hours.

The gross energy of diets were determined using a Parr 1281 adiabatic bomb calorimeter (Parr Instrument Company, Moline, IL, USA). The diets and digesta were also
analysed for selected minerals (P, Ca, Cu, K, Mg, Mn, Na, Sr, Fe and Zn). Samples were wet acid digested using nitric acid and hydrogen peroxide prior to the determination of mineral concentration by Inductively Coupled Plasma-Optical Emission Spectroscopy using a Perkin Elmer OPTIMA 7300 (Perkin Elmer Inc, Waltham, MA, USA). Nitrogen concentration of samples was determined by the Dumas method using a FP-428 nitrogen analyser (LECO® Corporation, St. Joseph, MI, USA) as described by Sweeny (1989). The acid insoluble ash component of dried diets and ileal digesta samples were determined according to the method of Siriwan et al. (1993). Data were analysed for significance by one-way ANOVA using JMP v 8.01 software (SAS Institute, Cary, NC, USA). Treatment differences were considered significant at P < 0.05. If significance was determined, a Tukey´s HSD was performed to differentiate between treatments.

The analysed concentration of Ca in diets was greater than formulated and is most probably due to higher than expected concentrations of Ca in the grains used (see Table 1). The influence of dietary Ca on feed intake, consumption of the separate Ca source and performance is shown in Table 1. Birds fed the basal diet containing 1.00% total Ca consumed significantly less feed and gained significantly less body weight during the experiment when compared with birds from the other treatment groups (P < 0.05). These results are in agreement with those of Rama Rao et al. (2006) who showed increased levels of dietary Ca depressed feed intake and weight gain in broilers. The feed efficiency of birds from the 1.00% Ca group was also significantly poorer than birds from the other groups (P < 0.05). There was no effect of treatment on the toe ash percentage.

Table 1. The effect of dietary calcium (Ca) concentration on the intake of a separate Ca source, total Ca intake and broiler performance (1- 21d of age)

The results from this current study show that the specific appetite for Ca is still active in modern commercial broilers and these were able to consume sufficient Ca to meet their requirement. There was a significant relationship between the Ca concentration of the mixed ration and intake of the separate Ca source (P < 0.0001) and this is in keeping with the results reported by Joshua and Mueller (1979). Birds fed diets containing 0.25% Ca consumed significantly more of the separate Ca source when compared to birds fed diets containing either 0.50, 0.75 and 1.00% Ca (P < 0.05). Birds offered diets with 0.50% Ca also consumed more of the separate Ca source than those fed 0.75 and 1.00% Ca diets (P < 0.05). The source of Ca as a proportion of the total Ca intake was influenced by the Ca concentration of the mixed ration (P < 0.0001). Calcium intake from the separate source accounted for approximately 63% of the Ca intake of birds fed the 0.25% Ca mixed ration which is in contrast to birds fed the 1.00% Ca diet where 19% of their total Ca intake was provided from the separate source (P < 0.05). Total Ca intake as a proportion of total feed increased with increasing dietary Ca concentration (P < 0.001). Birds fed the low Ca diet consumed significantly less Ca than the other treatment groups (P < 0.05).

The influence of Ca concentration of the mixed ration on the apparent ileal digestibility of minerals is summarised in Table 2. Calcium digestibility was significantly lower for birds fed 0.25% Ca when compared to birds fed 0.50 and 0.75% Ca diets (P < 0.05). Dietary calcium concentration affected the digestibility of Cu with birds fed 0.75% Ca showing a significantly greater digestibility coefficient than birds from the other three treatment groups (P < 0.05). The ileal digestibility of P and K and Mg showed an inverse relationship to the Ca concentration of the basal diet. As Ca concentration increased, the digestibility of P, K and Mg decreased. Manganese and Zn digestibility were significantly greater in birds reared on 0.50% Ca diets when compared to those formulated with 0.25 and 1.00% Ca (P < 0.05). There was no effect of diet on the digestibility of Fe, Na and Sr. Increasing the utilisation of phytate-P by broilers would reduce the dependence on inorganic sources of P and lower the total P currently used in poultry diets (Tamim and Angel, 2003). By reducing the concentration of dietary Ca and therefore limestone inclusion in the mixed ration may provide an opportunity for greater phytate-P utilisation through increased phytase (endogenous and exogenous) efficacy (Angel et al., 2002). The results from this study show that lowering the Ca concentration of the basal diet while providing a separate source of Ca had no adverse effect on bird performance or bone mineralisation (toe ash %). In contrast, birds that were fed diets with 1.00% Ca consumed significantly more total Ca and had poorer performance than their counterparts and is most probably a result of the dietary Ca:P ratio. Further research investigating the use of phytase, dietary P concentration and commercial application are planned.

Table 2. Influence of basal dietary Ca concentration on the apparent ileal digestibility coefficients of selected minerals for broilers offered a separate source of Ca

ACKNOWLEDGMENTS

The authors are grateful to the Australian Rural Industries Research and Development Corporation Chicken Meat Program for their financial support of this study.

REFERENCES

Angel, R, Tamim, NM, Applegate, TJ, Dhandu, AS, Ellestad, LE (2002) Journal of Applied Poultry Research 11, 471-480.

Driver, JP, Pesti, GM, Bakalli, RI, Edwards, HMJ (2005) Poultry Science 84, 1629-1639.

Forbes, JM, Shariatmadari, F (1994) Worlds Poultry Science Journal 50, 7-24.

Hughes, BO, Wood-Gush, DGM (1971) Animal Behaviour 19, 490-499.

Joshua, IG, Mueller, WJ (1979) British Poultry Science 20, 481-490.

Kempster, HL (1916) Journal of the American Association of Instructors and Investigators in Poultry Husbandry 3, 26-28.

Newman, RK, Sands, DC (1983) Physiology & Behavior 31, 13-19.

Rao, SVR, Raju, M, Reddy, MR, Pavani, P (2006) Animal Feed Science and Technology 131, 133-148.

Rugg, WC (1925) Victoria Department of Agriculture Bulletin 54, 36-56.

Selle, PH, Cowieson, AJ, Ravindran, V (2009) Livestock Science 124, 126-141.

Siriwan, P, Bryden, WL, Mollah, Y, Annison, EF (1993) British Poultry Science 34, 939-949.

Steinruck, U, Roth, FX, Kirchgessner, M (1990) Archiv Fur Geflugelkunde 54, 173-183.

Sweeney, RA (1989) Journal of the Association of Official Analytical Chemists 72, 770-774.

Tamim, NM, Angel, R (2003) Journal of Agricultural and Food Chemistry 51, 4687-4693.

Wood-Gush, DGM, Kare, MR (1966) British Poultry Science 7, 285-290.

Zuberbuehler, CA, Messikommer, RE, Wenk, C (2002) Journal of Nutrition 132, 3411-3417.

This paper was presented at the  23rd Annual Australian Poultry Science Symposium, in Sidney, New South Wales from February 19-22, 2012. Engormix.com thanks the organizing committee and the authors for this contribution.