Calcium bioavailability of different organic and inorganic dietary Ca sources (citrate, lactate, acetate, oyster-shell, eggshell, β-tri-Ca phosphate)

Adult dogs are capable of regulating calcium balance, with no adverse effects on health, when fed a high-calcium diet

Although the implications of long-term high Ca intakes have been well documented in growing dogs, the health consequences of Ca excess in adult dogs remain to be established. To evaluate the impact of feeding a diet containing 7·1 g/4184 kJ (1000 kcal) Ca for 40 weeks on Ca balance and health parameters in adult dogs, eighteen neutered adult Labrador Retrievers, (nine males and nine females) aged 2·5-7·4 years were randomised to one of two customised diets for 40 weeks. The diets were manufactured according to similar nutritional specifications, with the exception of Ca and P levels. The diets provided 1·7 and 7·1 g/4184 kJ (1000 kcal) (200(SD26) and 881(SD145) mg/kg body weight0·75 per d, respectively) Ca, respectively, with a Ca:P ratio of 1·6. Clinical examinations, ultrasound scans, radiographs, health parameters, metabolic effects and mineral balance were recorded at baseline and at 8-week intervals throughout the study. Dogs in both groups were healthy throughout the trial without evidence of urinary, renal or orthopaedic disease. In addition, there were no clinically relevant changes in any of the measures made in either group (all P>0·05). The high-Ca diet resulted in a 3·3-fold increase in faecal Ca excretion (P0·05). Ca intakes of up to 7·1 g/4184 kJ (1000 kcal) are well tolerated over a period of 40 weeks, with no adverse effects that could be attributed to the diet or to a high mineral intake.

Bioavailability of zinc glycinate in comparison with zinc sulphate in the presence of dietary phytate in an animal model with Zn labelled rats

The objective of this study was to quantify the bioavailability of zinc (Zn) from sulphate and glycinate as representatives of inorganic and organic zinc sources. The semi-synthetic basal diet contained 2 microg/g of native Zn and was fortified with pure sodium-phytate (8 g/kg) in order to simulate conditions of common cereal-based meals. The basal diet was supplemented with either 53 microg/g of Zn from sulphate (control) or 10 microg/g of Zn from either sulphate (ZnSulphate) or glycinate (ZnGly). Twenty-four (65)Zn-labelled, growing rats weighing 133 g were allotted to the three diets (eight animals per treatment) and were kept pair-fed to ZnSulphate for 15 days. Zn contents in blood plasma, femur and whole body, as well as, plasma alkaline phosphatase activities were reduced compared with control indicating a zinc deficiency in ZnSulphate and ZnGly treatment. This allowed their differentiation in zinc bioavailability. True absorption of dietary Zn was significantly higher in ZnGly than in ZnSulphate (51% vs. 44%) while losses of endogenous faecal Zn and urinary Zn were not affected to a quantitatively relevant extent (mean: 17% and 2% of intake). This resulted in a +30% significantly improved Zn retention for ZnGly (33% vs. 25%) and a lower severity on Zn deficiency symptoms compared with ZnSulphate. Metabolic utilization accounted for 95% of absorbed dietary Zn for both Zn sources. Overall, the bioavailability of zinc glycinate was significantly superior by 16% to zinc sulphate (49% vs. 42%), mainly because of a higher absorptive potential at presence of a strong anti-nutritive component (phytate) in the diet.