International Journal of Poultry Science 8 (4): 342-348, 2009 ISSN 1682-8356 © Asian Network for Scientific Information, 2009 342 Effect of Different Calcium Sources and Calcium Intake on Shell Quality and Bone Characteristics of Laying Hens at Sexual Maturity and End of Lay K.C. Koutoulis , I. Kyriazakis , G.C. Perry and P.D. Lewis 1 2 3 Division of Animal Health and Husbandry, School of Veterinary Science, 1 University of Bristol, Langford House, Langford, Bristol, England Laboratory of Nutrition, Husbandry and Animal Behaviour, 2 Faculty of Veterinary Medicine of Karditsa, University of Thessaly, Karditsa, Greece Animal and Poultry Science, University of KwaZulu-Natal, Pietermaritzburg, South Africa 3 Abstract: The influence of supplemental calcium given in flour or granular form and calcium intake on bone properties and egg characteristics of brown-egg laying hens was investigated at sexual maturity and at end of lay. Physical and mechanical bone characteristics were determined using 3-point and torsional tests. There was no effect of calcium source on the measured bone characteristics at sexual maturity. Bone breaking strength was positively correlated with both stiffness and total calcium intake. At 72 weeks, birds which had been offered additional calcium of either source exhibited considerably higher bone breaking strength than did control birds. Bone stiffness of birds offered limestone granules was significantly higher than control birds. Regression analysis showed strong relationships between calcium intake, bone stiffness and breaking strength. Shell quality was significantly better for birds consuming limestone in a granular form than for control birds. Shell quality for birds given limestone flour was intermediate between the other two groups. It is concluded that calcium supplementation increases egg quality, mechanical properties of the bone and as a consequence, may be able to reduce the risk of broken bones at the end of laying period. These effects are independent of the form of the supplemented calcium. Key words: Osteopenia, calcium, shell quality, bone strength INTRODUCTION Osteopenia is a loss of bone mass due to osteomalacia and/or osteoporosis resulting in bone fragility and possible adverse effects on the performance, health and welfare of birds (Webster, 2004; Whitehead and Fleming, 2000). The immediate and predisposing causes which can lead to a bone mass loss have been investigated; the effects of exercise (Knowles and Broom, 1990), different genotypes (Knowles et al., 1993), sexual maturity (Koutoulis et al., 1997b), nutritional deficiencies (Roland and Rao, 1992), use of perches (Hughes et al., 1993), cage height (Moinard et al., 1998) and different husbandry systems (Jendral et al., 2008; Fleming et al., 1994) on bone strength have been examined at various stages of the hen’s life, but with current systems for caged layers it is unlikely that radical changes could be introduced. Further improvement in bone strength is likely to come from genetic selection and dietary supplementation. Although nutritional approaches have been the most commonly adopted, the involvement of nutrition is still being questioned (Fleming et al., 2006; Whitehead, 1996). Deficiencies and imbalances of calcium, phosphorus or cholecalciferol have been shown to result in osteomalacia (Wilson and Duff, 1991). Conversely, increased calcium concentration in the diet (Cheng and Coon, 1990a; Frost and Roland, 1991) and supplementation of calcium in various forms and particle sizes (Fleming et al., 2003; Fleming et al., 1998; Cheng and Coon, 1990b; Hellwig and Waldroup, 1985) have been shown to improve most bone characteristics. The beneficial effect of additional calcium from different sources has also been well documented (e.g. Proudfoot and Hulan, 1987; Cheng and Coon, 1990b). It has been demonstrated that a progressive loss of structural bone occurs throughout the laying year and results in increased incidences of bone fragility and broken bones (Whitehead and Wilson, 1992). Structural bone mass at the end of the laying year depends on peak bone mass obtained during the growing period and on the rate of bone loss during the laying period. There have been few studies of the effect of pubertal calcium supply on structural bone characteristics at sexual maturity (Hurwitz and Bar, 1971). There is also a dearth of information on bone characteristics related to feeding calcium in a particular form throughout the laying period. This experiment was conducted to test the hypotheses that (a) an improvement on bone properties, physical or mechanical, could be achieved by supplying the birds with a different source of calcium during the rearing