Phosphorus equivalency of exogenous phytase relative to phosphorus in monosodium phosphate in broiler chickens.

The objective of this study was to estimate phosphorus (P) equivalency of exogenous phytase relative to P from monosodium phosphate (MSP) in broiler chickens. To attain this objective, the impact of dietary MSP or exogenous phytase on growth performance, ileal digestibility of P, and bone characteristics in broiler chickens was assessed. Six experimental diets consisting of a P-deficient basal diet based on corn and soybean meal, basal diet plus 0.9 or 1.8 g/kg of inorganic P from MSP, and basal diet plus 500, 1,000, or 2,000 FYT/kg of exogenous phytase. Calcium to P ratio in all diets was maintained at 1.5:1. A total of 576 male broiler chickens (Cobb 500; initial BW = 190 ± 17 g) on d 8 post hatching were allotted to the 6 dietary treatments in a randomized complete block design using BW as a blocking factor. Each dietary treatment contained 8 replicate cages with 12 birds per cage. On d 11 post hatching, 7 birds from each cage were euthanized by CO2 asphyxiation and dissected for the collection of ileal digesta. On d 18, ileal digesta were also collected from the remaining 5 birds in each cage. The left femur and tibia were collected from the bird with the median BW on d 11 and 18 from each cage, and analyzed for bone breaking strength and bone ash. Weight gain and gain-to-feed ratio linearly or quadratically increased (P < 0.05) in every period as the inclusion rate of MSP or phytase increased. Ileal digestibility of P linearly increased (P < 0.05) on d 11 with increasing MSP, but there was no significant effect on d 18. Increasing phytase concentration linearly increased (P < 0.05) ileal digestibility of P on d 11 and 18. Increasing dietary MSP or phytase linearly increased ileal digestible P concentration in diets (P < 0.05). Bone breaking strength and bone ash linearly or quadratically increased (P < 0.05) with increasing inclusion rate of MSP or phytase on d 11 and 18. The equivalency of 1,000 FYT/kg of exogenous phytase based on dietary ileal digestible P concentration was 1.5 and 1.2 g/kg of inorganic P in diets on d 11 and 18, respectively. The current results showed that the supplementation of MSP or exogenous phytase can increase growth performance, ileal P digestibility, bone breaking strength, and bone ash in young broiler chickens.

Comparison of Bone Mineral Content of the Equine Third Metacarpal to Total Radiographic Bone Aluminum Equivalents From Unprocessed Digital Radiographs.

Digital radiographs are common for estimating bone mineral content (BMC) in horses with radiographic bone aluminum equivalents (RBAE). Processing algorithms are used to produce clearer images of digital radiographs in clinical settings, but this distorts RBAE. This study compared RBAE from digital radiographs to BMC from bone ash, and physical and digital morphology measurements. Digital radiographs were taken of six third metacarpals (MCIII) from equine cadavers with an aluminum step wedge penetrometer. A 2-cm transverse section of bone was digitally analyzed and excised from each MCIII. For each image, a linear regression was created using the step wedge thicknesses (R2 > 0.99) and used to obtain total and individual RBAE. Outer and inner diameters of both dorsal-palmar (DP) and lateral-medial (LM) aspects, as well as cortical thicknesses, were measured physically and digitally. Bone samples were ether-extracted, oven-dried, and ashed. Statistics were analyzed as correlations between variables. Physical and digital measurements of dorsal, medial, and lateral cortices, as well as DP outer diameter, tended to be similar (r > 0.74, P < .09) but palmar cortex measurements did not (r = 0.41, P = .42). The LM outer and DP/LM inner diameters were similar between the two methods (r > 0.95, P < .05). Total RBAE was strongly correlated to BMC (r > 0.93, P < .01). These results suggest that using digital radiographs to make morphological measurements is accurate and confirm the strong relationship between total RBAE and bone ash. However, this study emphasizes the need to use unprocessed radiographs for analysis.