Nutritional geometry of calcium and phosphorus nutrition in broiler chicks. Growth performance, skeletal health and intake arrays

Abstract

The interaction between calcium (Ca) and non-phytate phosphorus (nPP) in broiler nutrition and skeletal health is highly complex with many factors influencing their digestion, absorption and utilisation. The use of an investigative model such as the geometric framework allows a graphical approach to explore these complex interactions. A total of 600 Ross 308-day-old male broiler chicks were allocated to one of 15 dietary treatments with five replicates and eight birds per replicate. Dietary treatments were formulated to one of three total densities of total Ca + nPP; high (15 g/kg), medium (13.5 g/kg) and low (12 g/kg) and at each density there were five different ratios of Ca : nPP (4, 2.75, 2.1, 1.5 and 1.14 : 1). Weekly performance data was collected and at the end of the experiment birds were individually weighed and the right leg removed for tibia ash analysis. Skeletal health was assessed using the latency to lie (LTL) at day 27. At low Ca and high nPP as well as high Ca and low nPP diets, birds had reduced feed intake, BW gain, poorer feed efficiency and lower tibia ash, resulting in a significant interaction between dietary Ca and nPP (P < 0.05). LTL times were negatively influenced by diets having either a broad ratio (high Ca, low nPP) or too narrow a ratio (low Ca, high nPP) indicating that shorter LTL times may be influenced by the ratio of Ca : nPP rather than absolute concentrations of either mineral. The calculated intake arrays show that broilers more closely regulate Ca intake than nPP intake. Broilers are willing to over consume nPP to defend a Ca intake target more so than they are willing to over consume Ca to defend an nPP target. Overall dietary nPP was more influential on performance metrics, however, from the data it may appear that birds prioritise Ca intake over nPP and broadly ate to meet this requirement. As broilers are more willing to eat to a Ca intake target rather than an nPP intake target, this emphasises the importance of formulating diets to a accurately balanced density of Ca : nPP considering the biological importance of both minerals.

Nutritional geometry of calcium and phosphorus nutrition in broiler chicks. The effect of different dietary calcium and phosphorus concentrations and ratios on nutrient digestibility

“…Bird performance, tibia ash and latency to lie results are presented in Bradbury et al (2014). The analysed Ca and P concentrations (Table 1) were within acceptable ranges Calcium phosphorus nutritional interactions when mixing and assay errors were considered.…”

“…Outside of the maximal 'hub', ileal N digestibility sharply decreased with reducing dietary Ca and nPP and moderately decreased with increased Ca and nPP in diets. Broadly speaking, these effects corresponded to maximal BW gain and the most efficient feed conversion during the experimental period (Bradbury et al, 2014).…”

“…Bird performance is reported in (Bradbury et al, 2014) and will be briefly discussed. Feed intake was highest in birds fed diets with high nPP and intermediate concentrations of Ca and lowest in birds fed high Ca and low nPP diets.…”

“…Animals and housing Birds in this study were housed according to the conditions outlined by Bradbury et al (2014). Briefly, a total of 600-dayold male Ross 308 chicks were obtained from a commercial hatchery.…”

“…However, limestone has a high acid binding capacity that is capable of increasing intestinal pH and creating a favourable environment for the formation of phytatenutrient complexes . At each Ca to nPP ratio, there was a tendency for improved nutrient digestibility, increased BW gain, feed intake and tibia ash (Bradbury et al, 2014) as the proportion of DCP increased in the diet and limestone reduced. However, direct comparisons are difficult since each Ca : nPP cluster also differed in Ca and nPP concentrations.…”