Short-term determination and long-term evaluation of the dietary methionine requirement in adult dogs

Abstract

Methionine, an essential sulphur-containing amino acid (SAA), plays an integral role in many metabolic processes. Evidence for the methionine requirements of adult dogs is limited, and we employed the indicator amino acid oxidation (IAAO) method to estimate dietary methionine requirements in Labrador retrievers (n 21). Using semi-purified diets, the mean requirement was 0·55 (95 % CI 0·41, 0·71) g/4184 kJ. In a subsequent parallel design study, three groups of adult Labrador retrievers (n 52) were fed semi-purified diets with 0·55 g/4184 kJ (test diet 1), 0·71 g/4184 kJ (test diet 2) or 1·37 g/4184 kJ (control diet) of methionine for 32 weeks to assess the long-term consequences of feeding. The total SAA content (2·68 g/4184 kJ) was maintained through dietary supplementation of cystine. Plasma methionine did not decrease in test group and increased significantly on test diet 1 in weeks 8 and 16 compared with control. Reducing dietary methionine did not have a significant effect on whole blood, plasma or urinary taurine or plasma N-terminal pro B-type natriuretic peptide. Significant effects in both test diets were observed for cholesterol, betaine and dimethylglycine. In conclusion, feeding methionine at the IAAO-estimated mean was sufficient to maintain plasma methionine over 32 weeks when total SAA was maintained. However, choline oxidation may have increased to support plasma methionine and have additional consequences for lipid metabolism. While the IAAO can be employed to assess essential amino acid requirements, such as methionine in the dog using semi-purified diets, further work is required to establish safe levels for commercial diet formats.

Minimum dietary methionine requirements in Miniature Dachshund, Beagle, and Labrador Retriever adult dogs using the indicator amino acid oxidation technique

“…In contrast, in the United Kingdom and Europe, factors of 4 kcal/g for protein and nitrogen-free extract and 9 kcal/g for fat are used (Atwater factors). As such, if you used the Atwater factors, rather than modified Atwater factors, the estimate of our requirement on a caloric basis would be 1.176 g/Mcal ME for the pooled requirement of Beagles and Labrador Retrievers and still greater than the estimate from Harrison et al (2020) . Further differences between these estimates may be due to the differences in digestibility ( Harrison et al, 2020 = 96% total tract apparent CP digestibility), whereas the digestibility of the diets used in the present study was likely lower due to the inclusion of more intact ingredients in contrast to the diets used by Harrison et al (2020) .…”

“…Recently, Harrison et al (2020) applied IAAO methods to estimate the dietary requirements of Met in adult Labrador Retrievers and determined an upper 95% CL of 0.71 g/Mcal, which is about 50% of the present recommendation (1.303 g/Mcal metabolizable energy [ ME ] for the pooled requirement of Beagles and Labrador Retrievers). One difference when comparing these estimates and presenting them as a function of dietary energy is that in North America, the ME content of the diet is calculated using factors of 3.5 kcal/g for protein and nitrogen-free extract and 8.5 kcal/g for fat (modified Atwater factors).…”

“…The latter is supported by the 30% lower Met requirement of piglets fed parenterally in contrast to enterally ( Shoveller et al, 2003 ) and that the gut utilizes 20% of dietary Met in healthy pigs ( Riedijk et al, 2007 ). It should also be noted that the diets used by Harrison et al (2020) had a much higher protein content and a lower ratio of indispensable AA to total nitrogen content. We do not know whether greater dispensable AA may have contributed to a lower estimate of the requirement, but this is an industry-relevant question to investigate.…”

“…Related to the study designs, there are also fundamental differences between these two studies. Harrison et al (2020) did not use the prime to constant ratio, which is based on the Phe kinetics that we conducted in dogs ( Gooding et al, 2013 ) and also explains the significantly lower F 13 CO 2 presented by Harrison et al (2020) . Furthermore, given that Gooding et al (2013) demonstrated that the gastric emptying rate is approximately 25 min, the once hourly feeding in Harrison et al (2020) may not have allowed for the achievement of a similar isotopic steady state.…”

“… Harrison et al (2020) did not use the prime to constant ratio, which is based on the Phe kinetics that we conducted in dogs ( Gooding et al, 2013 ) and also explains the significantly lower F 13 CO 2 presented by Harrison et al (2020) . Furthermore, given that Gooding et al (2013) demonstrated that the gastric emptying rate is approximately 25 min, the once hourly feeding in Harrison et al (2020) may not have allowed for the achievement of a similar isotopic steady state. Finally, we validated that metabolic chambers resulted in complete CO 2 collection and did not result in any fractionation of the breath sample ( Shoveller et al, 2017 ), but it was unclear how Harrison et al (2020) had done the same using respiratory masks.…”