Diet restriction and ageing in the dog: major observations over two decades.

This report reviews decade two of the lifetime diet restriction study of the dog. Labrador retrievers (n 48) were paired at age 6 weeks by sex and weight within each of seven litters, and assigned randomly within the pair to control-feeding (CF) or 25 % diet restriction (DR). Feeding began at age 8 weeks. The same diet was fed to all dogs; only the quantity differed. Major lifetime observations included 1.8 years longer median lifespan among diet-restricted dogs, with delayed onset of late life diseases, especially osteoarthritis. Long-term DR did not negatively affect skeletal maturation, structure or metabolism. Among all dogs, high static fat mass and declining lean body mass predicted death, most strongly at 1 year prior. Fat mass above 25 % was associated with increasing insulin resistance, which independently predicted lifespan and chronic diseases. Metabolizable energy requirement/lean body mass most accurately explained energy metabolism due to diet restriction; diet-restricted dogs required 17 % less energy to maintain each lean kilogram. Metabonomics-based urine metabolite trajectories reflected DR-related differences, suggesting that signals from gut microbiota may be involved in the DR longevity and health responses. Independent of feeding group, increased hazard of earlier death was associated with lower lymphoproliferative responses to phytohaemagglutinin, concanavalin A, and pokeweed mitogen; lower total lymphocytes, T-cells, CD4 and CD8 cells; lower CD8 percentages and higher B-cell percentages. When diet group was taken into account, PWM responses and cell counts and percentages remained predictive of earlier death.

Influence of lifetime food restriction on physiological variables in Labrador retriever dogs.

Effects of lifetime food restriction on erythrocytes and numerous clinical chemistry, thyroid, parathyroid, and acid-base variables are reported from a paired-feeding study of 25% diet restriction in dogs. The 48 dogs were paired by gender and weaning weight within litter, and 1 dog in each pair was fed 25% less than its pair mate, from age 8 weeks until death. Erythrocyte and serum biochemistry profiles were evaluated by annual sampling intervals and longitudinally. Erythrocyte variables were slightly higher among control-fed dogs, a possible reflection of the need to support both higher body fat mass and lean mass that uses energy less efficiently. Among serum biochemistry variables, glucose and triglyceride were lower among diet-restricted dogs, while creatinine was slightly higher in the absence of renal disease or failure, over the life spans of the dogs. Glucose outcomes reflect improved glucose tolerance that has been demonstrated with diet restriction protocols in several species, while triglyceride data may reflect the difference in total body fat cells between feeding groups. Creatinine outcomes may reflect lean mass responses to diet restriction or more efficient function of the intracellular proteasome. Serum triiodothyronine levels were lower among diet-restricted dogs. Other clinical chemistry and thyroid variables, parathyroid variables, and acid-base variables were not strongly influenced by diet restriction but revealed age-related effects.

Antioxidant status of pair-fed labrador retrievers is affected by diet restriction and aging.

Twenty-four sibling pairs of 8-wk-old Labrador Retrievers were assigned to an experiment to determine the effects of diet restriction (75% of control-fed pair mate) on the quality and span of canine life and to identify biological markers of aging in dogs. The antioxidant status of these dogs was monitored by annual assays for serum retinol (RT), retinyl palmitate (RP), total vitamin A (VA), vitamin E (VE), selenium (Se), copper (Cu), and ceruloplasmin (Cp), plasma ascorbic acid (AA), uric acid (UA), and total peroxyl-radical trapping activity (TRAP), and whole-blood glutathione peroxidase (Gpx). Data in this report are for the 6-y period of the experiment when the dogs were between 5 and 10 y of age. Diet restriction reduced RT, VE, Cu, and Cp. Aging was associated with decreased RP, VA, VE, Se, and Cu and with increased RT, Cp, and Gpx. Female dogs had lower RP, VA, Cu, and Cp than male dogs. Litter effects were observed for VE, Cu, UA, and Gpx. Treatment effects on serum RT and Cu suggest that these variables are not as regulated homeostatically by hepatic storage as in most other species. Although the antioxidant profiles did not elucidate how diet restriction contributes to longevity, they have the potential to enhance our understanding of canine clinical nutrition and to have practical applications in formulating canine diets.

Effects of diet restriction on life span and age-related changes in dogs.

OBJECTIVE: To evaluate the effects of 25% diet restriction on life span of dogs and on markers of aging. DESIGN: Paired feeding study. ANIMALS: 48 Labrador Retrievers. PROCEDURES: Dogs were paired, and 1 dog in each pair was fed 25% less food than its pair-mate from 8 weeks of age until death. Serum biochemical analyses were performed, body condition was scored, and body composition was measured annually until 12 years of age. Age at onset of chronic disease and median (age when 50% of the dogs were deceased) and maximum (age when 90% of the dogs were deceased) life spans were evaluated. RESULTS: Compared with control dogs, food-restricted dogs weighed less and had lower body fat content and lower serum triglycerides, triiodothyronine, insulin, and glucose concentrations. Median life span was significantly longer for dogs in which food was restricted. The onset of clinical signs of chronic disease generally was delayed for food-restricted dogs. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that 25% restriction in food intake increased median life span and delayed the onset of signs of chronic disease in these dogs.