If you have ever had a pet with kidney stones, you know that diet can be a major contributing factor to their formation. This is why veterinarians often recommend providing animals with foods higher in water content and switching to a diet that promotes a healthy urine pH (not too basic, not too acidic).
Did you know that bottlenose dolphins can develop kidney stones too? The particular kind of stone they develop is typically entirely comprised of ammonium urate. As with other mammals that develop kidney stones, if left untreated, they can lead to illness and even death. While stones sometimes occur in free-ranging dolphins, they are more common in captive animals.
A new study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology examined the role of diet in the development of these stones and ways to prevent them. They targeted diet as captive bottlenose dolphins are typically fed an acidic diet higher in purines and lower in water than what the animals would normally consume in the wild. In fact, ammonium and uric acid increase in captive bottlenose dolphins following a typical fish meal. Such high concentrations of ammonium can precipitate (or come out of solution) and result in the formation of stones.
Armed with this information, the researchers developed a modified diet that included more free-range fish with a similar purine content but higher in pH (more alkaline due to a higher calcium content – think teeth and spines) and protein that their typical captive diet. In addition, the animals were supplemented with 2-4 L of fresh water every day. They fed this modified diet to older dolphins (18-43y) with kidney stones and saw decreases in urinary ammonium as well as decreases in blood uric acid. Therefore, they suspect that modifying the diet may be a useful strategy to help reduce the risk of kidney stones, although a longer study would be needed to confirm their hypothesis.
JM Meegan, AJ Ardente, JR Poindexter, M Baird, B Novick, C Parry, ED Jensen, S Venn-Watson, K Sakhaee, CR Smit. Dietary effects on urinary physicochemistry in Navy bottlenose dolphins (Tursiops truncates) for the prevention of ammonium urate kidney stones. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. 321(5): R723-R731, 2021.