Newfoundlands have lower rates of taurine biosynthesis than beagles

Large dogs are more likely than small dogs to have taurine deficiency-induced dilated cardiomyopathy. Newfoundlands appear to be one of the large breeds most susceptible to developing taurine deficiency. We hypothesize that the breed disposition is the result of a low taurine biosynthesis capability. To evaluate the relative taurine biosynthetic capability of Newfoundlands, the taurine biosynthetic rates (TBRs) of six privately owned Newfoundlands (54.2 ± 3.4 kg, mean ± SEM) and six purposebred beagles (12.3 ± 0.25 kg) were measured using the stable isotopic taurine (D4-tau) dilution technique. All dogs were adapted for 3 weeks to the same Association of American Feed Control Officials (AAFCO) protocol-tested commercial dry-type diet containing 0.54% sulfur amino acids (SAAs) and 0.022% taurine. Sufficient food was given to maintain an ideal body condition score. After a single oral dose of D4-tau, the ratio of D4-tau:H4-tau in urine collected daily for 6 days was measured by gas chromatography-mass spectrometry (GC-MS) to determine TBR. Plasma, whole blood, and urinary taurine concentrations were also measured. The TBR of Newfoundlands versus that of beagles was 36.7 ± 4.3 versus 91.8 ± 9.0 mg/kg BW ^0.87/day (kg BW ^0-87 = relative metabolic liver weight; P < .01), respectively. Plasma, whole blood, and urine taurine concentrations of Newfoundlands versus beagles were 48.9 ± 7 versus 96.6 ± 11 nmol/ml (P < .01), 201 ± 22 versus 277 ± 20 nmol/ml (P < .05), and 124 ± 41 vs. 933 ± 228 nmol/mg creatinine (P < .05), respectively. These results support the hypothesis that there is a breed or size difference in taurine biosynthetic capability when dogs are fed diets near limiting in dietary SAA but adequate in amounts to maintain body weight. It appears that the low TBRs of Newfoundlands account for the more frequent observation of taurine-deficiency dilated cardiomyopathy in Newfoundlands relative to that of small-breed dogs.