Effects of nutritional intervention on dogs diagnosed with early-stage myxomatous mitral valve disease

Abstract

Myxomatous mitral valve disease (MMVD) is the most prevalent cardiovascular disease in the domestic dog. The disease is characterized by degradation of the mitral valve which results in blood backflowing into the left atrium when the left ventricle contracts, leading to the dilation of the left atrium and left ventricle. Dogs with cardiovascular disease should be fed nutrition to support cardiovascular health, but optimal levels of key nutrients are not well defined for canine MMVD. It was hypothesized that a food formulated to contain increased levels of protein, fat, L-carnitine, taurine, omega-3 fatty acids, and moderate sodium levels (test food) would show evidence of reduced disease progression and support aspects of quality of life compared to a food without elevated levels of key nutrients (control food). Therefore, this study investigated effects of two foods designed to support cardiac health with differing levels of key nutrients in dogs diagnosed with MMVD. The two-by-two factorial study enrolled dogs with MMVD and dogs without MMVD (healthy dogs). The MMVD dogs were stratified and the healthy dogs were randomized to one of two treatment groups, test food (MMVD-TEST group and HEALTHY-TEST group) or control food (MMVD-CONTROL group and HEALTHY-CONTROL group), for 6 months following a 5-week washout period. At the start of the washout period, 10 dogs with MMVD and 10 healthy dogs were enrolled. Of the dogs enrolled, four dogs in the MMVD-TEST group, two dogs in the MMVD-CONTROL groups, four dogs in the HEALTHY-TEST group, and five dogs in the HEALTHY-CONTROL group completed the 6-month feeding study. Caloric intake (kcal/metabolic body weight/day), body weight (BW), body condition score (BCS), muscle condition score (MCS), and blood and urine biomarkers were assessed in dogs with MMVD and healthy dogs. Echocardiographic measurements were assessed in only the MMVD dogs. The MMVD-TEST group maintained (P > 0.10) caloric intake, BW, and BCS, but had increased (P ≤ 0.05) muscle wasting throughout the study. The MMVD-CONTROL group had reduced (P ≤ 0.05) caloric intake throughout the study, but maintained (P > 0.10) BW, BCS, and MCS. There was no difference (P > 0.10) in MCS between the two MMVD treatment groups throughout the study, but the MMVD-CONTROL group had lower caloric intake (P ≤ 0.05) compared to the MMVD-TEST group at various timepoints. Caloric intake, BW, BCS, and MCS were overall maintained (P > 0.10) in the HEALTHY-TEST group and HEALTHY-CONTROL group throughout the study. Both the MMVD-TEST group and MMVD-CONTROL group maintained their MMVD stage throughout the study. Anteroposterior left atrial diameter (LAD), left ventricular internal diameter at end-diastole (normalized for body weight) (LVIDdN), and left ventricular internal diameter at end-systole (LVIDs) decreased by 6% (P = 0.30), 12% (P = 0.03), and 6% (P = 0.23), respectively, in the MMVD-TEST group at 6 months compared to baseline. In the MMVD-CONTROL group, LAD, LVIDdN, and LVIDs increased by 6% (P = 0.54), 11% (P = 0.15), and 20% (P < 0.01), respectively, at 6 months compared to baseline. There was no difference (P > 0.10) in left atrial size between the two MMVD treatment groups throughout the study, but LVIDs and LVIDdN was larger (P ≤ 0.05) in the MMVD-CONTROL group compared to the MMVD-TEST group at the end of the study. Additionally, this research explored the effects of the two study foods on clinical biomarkers and sought to identify exploratory biomarkers associated with canine MMVD. All four treatment groups remained above the lower limit of normal for whole blood taurine (200 nmol/L) and serum 25-hydroxyvitamin D (112 nmol/L) supporting the concept that early-stage MMVD dogs are not at risk for taurine deficiency or low serum vitamin D levels. Although these results should be validated with a longer, larger, and more diverse study since the present study was underpowered and should be considered a pilot study, this research contributes to the existing data of nutritional intervention in dogs with MMVD.