RESUMEN
The present study aimed to investigate the effect of the combination of a water-soluble calcium (Ca) source (CaCl2) with a water-soluble phosphorus (P) source (NaH2PO4*2H2O, diet soluble, SOL) in comparison to a water-insoluble P source (CaHPO4*2H2O, diet insoluble, INS) on apparent digestibility and renal excretion of Ca and P in dogs. The Ca intake was 226 mg/kg bodyweight (bw), the Ca/P ratio 1.9/1 in SOL and 2.0/1 in INS. The percentage of Ca from CaCl2 was 60% in SOL and 33% in INS. Eight adult Foxhound-crossbred dogs FBI, (3-5 years, bw 24-32 kg) were available. Standard digestion trials were carried out (10 days adaptation, 5 days total faecal collection). Spontaneously excreted urine was collected pre- and postprandially. In vitro water solubility of P in the mineral premixes was determined. The Ca digestibility was negative in both trials without significant differences between the groups. Apparent P digestibility was increased in group SOL (26% vs. 20% in INS). In both groups, P content in urine was higher pre- compared to postprandial, with higher concentrations in group SOL. The same was true for the P/Crea ratio. The water solubility of P in the mineral premixes used in the trials showed considerable differences: The P in premix INS was insoluble in water after 1 and after 90 min. By contrast, the P in the premix SOL was highly soluble (98%) after 1 minute. After 90 min, however, the P solubility decreased to 43%, suggesting the formation of insoluble CaP salts, presumably from CaCl2 and NaH2PO4*2H2O. In conclusion, in the present study, apparent Ca digestibility in dogs was not affected by the solubility of Ca and P, while P digestibility and renal P excretion increased.
RESUMEN
The study aimed to investigate the effect of faecal dry matter (DM) excretion on faecal losses of calcium (Ca) and phosphorus (P) without potentially confounding factors. Dogs were fed two levels of the same basal diet (cooked pork, rice, gelatine; 8.5 ± 0.7 and 12.6 ± 1.2 g DM/kg BW). Mineral supplements were added separately for identical Ca and P supply independent of DM intake (Ca 226 and P ~170 mg/kg BW). Digestion trials (10 days adaptation, 5 days quantitative faecal collection) were carried out. Digestibility of DM averaged 87% in both trials. Faecal DM and mineral excretion increased highly significant (DM 1.1 ± 0.3 to 1.7 ± 0.2 g/kg BW, p = 0.00005; Ca 185 ± 34 and 233 ± 22 mg/kg BW, p = 0.00119; P 99 ± 23 to 127 ± 12 mg/kg BW, p = 0.00212), revealing a highly significant correlation. Apparent digestibility of Ca was positive in the first trial and negative in the second leading to a slightly negative Ca retention in the latter one. The results suggest that in dogs (i) factors influencing Ca and P absorption can only be compared if faecal DM excretion is identical and (ii) Ca requirements may be affected by DM intake and digestibility.