An evaluation of various response criteria in assessing biological availability of phosphorus for broilers.

The relative bioavailability of P from seven sources was determined in relation to a standard dicalcium phosphate dihydrate (CaHPO4.2H2O) in a 21-d assay involving 1,320 broiler male chicks using several response criteria. The seven sources (Lucaphos-48, Lucaphos-40, Rukana, Cefkaphos-N, phosphoric acid, monocalcium phosphate monohydrate, or Biophos) were added to the basal diet (.40% total P and 1.10% Ca) at levels to supply .05, .08, .12, .17, .23, and .32% P. Two additional levels (.44 and .66%) of P from dicalcium phosphate dihydrate were included for the standards. The criteria selected to evaluate included tibia ash, tibia specific gravity, tibia shear force, toe shear force, and metatarsal shear force. Other criteria: weight, length, diameter, and volume of tibia; weight, volume, and specific gravity of metatarsus; and weight, volume, and specific gravity of toe were not selected because their response to increasing P levels were inconsistent and quite variable. Nonlinear (asymptotic and sigmoidal) regression equations were fitted to the data than linear equations. The ratios of regression coefficients were used to determine the bioavailability of various test phosphates relative to the reference standard. The results indicated that the response criteria used for the determination will considerably influence the relative bioavailability estimates of a P source. Body weight gain and toe ash percentage were found to be an equally or a more sensitive criteria for assessment of P availability than tibia ash. Tibia specific gravity, tibia shear force, toe shear force, and metatarsal shear force were of limited value as response criteria in P bioavailability assays based on standard error and difference required for significance.

Stimulation of growth by intravenous injection of copper in weanling pigs.

This study was conducted to examine whether Cu could exert its growth-promoting effect when injected, rather than being fed, and thus bypass the gastrointestinal tract. In two 18-d experiments, pigs were injected every 2 d with a Cu histidinate or histidine solution. Amounts of Cu injected were calculated to simulate varying absorption rates in pigs fed 250 ppm of dietary Cu. In Exp. 1, 44 pigs were randomly assigned to four groups of 11 pigs each. Pigs were injected with four levels of Cu histidinate (0, 5, 10, and 15% estimated apparent absorption coefficients based on calculated feed intake). Average daily gain responded quadratically (P < .05) to levels of Cu histidinate; maximum growth was seen in the 5% group. At d 6, serum mitogenic activity also exhibited a similar quadratic response (P < .05). In Exp. 2, estimated Cu absorptions of 0, 2, 4, 6, and 8% were tested. Forty-five pigs were randomly assigned to five groups of nine pigs each and injected as in Exp. 1. Both ADG and serum mitogenic activity displayed a quadratic response (P < .05); the maximum response was seen in the 4% group. Liver Cu content, superoxide dismutase activity, and serum Cu concentrations were linearly increased (P < .05) with increasing dosage of Cu in both Exp. 1 and 2. Also, brain Cu content linearly increased (P < .05) with increasing dosage of Cu in both Exp. 1 and 2. Also, brain Cu hormone mRNA concentrations in Exp. 2 were not significantly influenced by treatments.(ABSTRACT TRUNCATED AT 250 WORDS)