Faecal calcium excretion does not decrease during long‐term feeding of a low‐calcium diet in adult dogs

Abstract

According to a previous meta-analysis, adult dogs do not notably increase calcium absorption from the gastrointestinal tract when calcium intake is decreased. This results in a negative calcium balance even with a moderate calcium reduction. In this study we wanted to verify (i) whether a negative calcium balance occurs at a calcium intake equivalent to NRC (2006) (Nutrient requirements of dogs and cats, 2006, The National Academies Press, Washington, DC) minimal requirements, and if so (ii) whether the negative calcium balance will persist for up to 6 months on a low-calcium diet. After a pre-feeding period of at least 18 weeks with calcium intake slightly exceeding maintenance requirements (200 mg/kg body weight ), 12 dogs (6 Beagles, 6 Foxhound crossbreds) were fed a low-calcium diet for 28 weeks. One dog was removed from the trial for reasons unrelated to the study at week 23. Calcium intake amounted to 60 mg/kg body weight corresponding to the minimal requirement for maintenance in dogs (NRC, 2006 (Nutrient requirements of dogs and cats, 2006, The National Academies Press, Washington, DC)). Digestion trials were carried out at week 7, 14, 21 and 28 of the low calcium feeding period. At these time points, and at week 18 of the pre-trial, blood samples were taken and analysed for calcium, ionised calcium, phosphorus, parathyroid hormone, vitamin D, serum crosslaps and bone alkaline phosphatase. Apparent calcium digestibility was negative throughout the study, suggesting a negative calcium balance. There was no systematic decrease in faecal calcium excretion. Serum calcium, ionised calcium and phosphorus remained within the reference range. Serum crosslaps increased continuously from baseline to week 28 of trial, with averages increasing from 0.102 ng/ml to 0.279 ng/ml, suggesting osteoclastic activity, indicative of calcium mobilisation from the skeleton. The study supports the theory of a lack of adaptation of intestinal calcium absorption from diets with relatively low calcium content in dogs. This agrees with clinical findings in dogs eating low-calcium diet.

Calcium and phosphorus metabolism in peripartal dogs

“…Independent of the number of foetuses, the apparent digestibility of calcium and phosphorus remained relatively low in the gestating bitches when compared to values given for adult dogs during maintenance (−20% to 44% vs. 5% to 50% apparent digestibility of calcium; 8%–54% vs. 46%–90% apparent digestibility of phosphorus; DLG, ). Schmitt et al () also found low and even negative values for the apparent digestibility of both elements in adult dogs during maintenance (−134% to 18% apparent digestibility of calcium, −28% to 49% apparent digestibility of phosphorus). Because growth is another period of increased calcium and phosphorus demand due to skeletal development, data from puppies were compared with results from the present study in peripartal dogs.…”

“…Based on our findings especially of the bone markers, which stayed within the reference range during the peripartal phase and did not indicate predominant bone resorption, we hypothesise that the recommendations for the daily supply with calcium and phosphorus in gestating dogs (DLG, ; FEDIAF ; Meyer et al, ; NRC, ) can be interpreted as sufficient to meet the requirements during this phase. A further increase of dietary calcium and phosphorus supply in peripartal dogs would probably not prevent a certain physiological increase of bone resorption because (a) adult dogs during maintenance did not adapt to a prolonged feeding of a low calcium diet (Schmitt et al, ) and (b) even species which regulate their mineral balance more via intestinal absorption than dogs do, use their skeletal stores during gestation (Bronner & Pansu, ; Malm, ; McKay et al, ; Potgieter, ; Walker, ).…”

“…Assuming that the reference ranges for crosslaps and bALP are also valid for peripartal dogs, the results of this study would suggest the recommended intake of both minerals according to NRC () suffices. However, the values of both crosslaps and bALP, determined with the same methods, were clearly lower in adult dogs of same breeds and ages during maintenance (Schmitt et al, ) indicating an increased bone turnover during the peripartal period. According to Allen (), age, diseases, surgery, medication and exercise, respectively, as well as biological variability within the population, might influence bALP.…”

“…Thus, decreasing the calcium losses via urine is a negligible way for dogs to maintain calcium homoeostasis. To maintain their calcium homoeostasis in case of an inadequate intake, adult dogs at maintenance therefore have to use their skeletal stores to a higher degree (Böswald, Dobenecker, Clauss, & Kienzle, ; Schmitt et al, ). In contrast, the phosphorus homoeostasis is regulated to a higher extend by renal excretion and use of tissue stores (Kiefer‐Hecker, Kienzle, & Dobenecker, ).…”

“…A meta-analysis about short-term studies (1-6 weeks) on apparent digestibility of calcium in dogs has shown that adult dogs at maintenance do not adapt their intestinal calcium absorption to different amounts of calcium in their diets (Mack, Alexander, Morris, Dobenecker, & Kienzle, 2015). Even dogs fed a low calcium diet for 6 months failed to decrease their faecal calcium losses (Schmitt et al, 2017). In times of adequate calcium intake renal calcium losses are low (10-15 mg/kg bodyweight [BW]) and are further reduced only slightly in case of low calcium intake (to ~5 mg/ kg BW) (Chen & Neuman, 1955;DLG, 1989).…”