Bone breaking strength and apparent metabolisability of calcium and phosphorus in selected and unselected broiler chicken genotypes

Abstract

1. The present study examined the bone strength and apparent mineral metabolisability of a selected broiler chicken compared with those of a relatively unselected genotype. 2. Selected (SB) and unselected genotypes (UB) were reared under standard conditions and were fed on either a high quality (HQ) or a low quality (LQ) diet. Tibiotarsi samples were collected at 42 d from SB and compared to tibiotarsi from UB of the same age and the same body mass (BM). 3. Bones were assessed for: bone breaking strength (BBS), morphology (weight and length), and both organic (OM) and inorganic content (ASH). Apparent dry matter digestibility and the coefficient of apparent metabolisability of calcium and phosphorus were determined at the same BM. 4. The BBS of SB (214 +/- 9 N) was greater than that of same-age UB (119 +/- 8 N) but the same as that of same-BM UB (218 +/- 10 N). At the same age, the SB had stronger, heavier bones with more ash and organic matter per unit length of tibiotarsus than UB. At the same BM, the tibiotarsi of the SB were shorter and lighter, with a higher ash and a similar organic content than the bones of the UB. At the same BM, BBS was about 15% lower in both genotypes fed on the LQ compared to the HQ diet. 5. The coefficients of apparent metabolisability of calcium and phosphorus were the same in both genotypes when fed on the HQ diet, but were lower in the SB than in the UB genotype when the birds were given the LQ diet. 6. The tibiotarsi of the selected broilers were stronger, or at least as strong, as those of the unselected broiler genotype, which may be due to similar levels of apparent calcium metabolisability of the selected chickens.

The effect of <i>Moringa oleifera</i> leaf meal supplementation on tibia strength, morphology and inorganic content of broiler chickens

“…Onyango et al (2006) reported an increase in ileal digestibility of dry matter, energy, nitrogen and P, but an accompanying decrease in the digestibility of Ca when the dietary level of P was increased. A similar observation was reported by McDevitt et al (2006), who notes that dry bone weight and mineral content per unit length of modern broiler strains increase in direct proportion to the increase in BW. In contrast, inadequate dietary sources of Ca result in blood hypocalcaemia, leading to reduced bone strength and mineralization (Talaty et al, 2009a).…”

“…Although tibia ash weight was not significantly different between T4 and T1, it was highest in T4 and lowest in T2 (P <0.05). This implies that the increase in dry bone weight and mineral content per unit bone length responds to mechanical forces placed on the bone (McDevitt et al, 2006;Whitehead, 2007;Talaty et al, 2009b). The weight of tibia ash has been found to be a more sensitive indicator of the amount of Ca and P in the diet (Hall et al, 2003).…”

“…This could have contributed to bone strength of birds from an early age; which might explain why there were no differences in tibia characteristics. Generally, broilers have been found to be sensitive to imbalances in mineral supply in their diets (McDevitt et al, 2006).…”

“…Absorption and homeostasis of these minerals depend on their dietary ratio, with maximum absorption obtained at 2Ca : 1P often met by supplying NRC (1994) recommendations of 10 g Ca and 4.5 g available P/kg in the broiler starter diet. Broilers are more sensitive to imbalances in mineral supply in their diets (McDevitt et al, 2006). Major ingredients in poultry diets are of plant origin and have approximately 60% -80% of phosphorus in phytic acid form and/or its salt phytate, rendering it biounavailable (Rao et al, 1999;Foidl et al, 2001).…”

“…In modern meat-type chickens, bone strength and development are closely linked to the expression of genetic potential for maximum lean muscle deposition (Williams et al, 2004). Thus, the increase in dry bone weight and mineral content per unit bone length responds to mechanical forces placed on the bone (McDevitt et al, 2006;Whitehead, 2007;Talaty et al, 2009a). Skeletal integrity of broiler chickens has become a welfare and economic concern (Williams et al, 2004;Almeida Paz & Bruno, 2006;Fleming, 2008).…”