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Adipose tissue
- Obesity is dependent on the amount of adipose tissue (fat) in the body NOT on weight
- White adipose: most common, found subcutaneously (under deepest layer of skin; insulation) as well as around organs (protective cushioning)
- Brown adipose: found between the shoulder, common in babies, mostly lost by adulthood. Can 'vibrate' to generate heat (thermogenesis)
 - Made up of adipocytes
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Adipokines
- Type of cytokine (adipocytokine) -> cell signalling protein
- Adipocytokines send signals all over the body (brain, reproductive system, gut) and give information on the exernal environment (availability of resources)
- The amount of adipose tissue influences the brain and body
- Leptin: (thin) hormone. Secreted by adipocytes and sends signals to the hypothalamus.
- > As it's secreted by adipocytes the amount of hormone in the body is dependent on the amount of adipose tissue.
- > Also known as the 'satiety' hormone; high levels inhibit appetite and increase energy expenditure while low levels increase appetite and decrease energy expenditure.
- > Leptin receptor KO mice, when given blood transfusion from healthy mice begin to show weightloss
- > Leptin resistance in hypothalamus can contribute to obesity; resistance can be caused by too high a level in the blood
- Adiponectin: most important adipose secretion
- > Decreases with increased body fat (negatively associated with adiposity)
- > Anti-inflammatory (so prevents cardiovascular disorders)
- > Increases fatty acid oxidation AND insulin sensitivity
- > Low levels increase risk for Type 2 diabetes, CVD, metabolic sydrome, hyperlipidaemia (high levels of triglycerides, cholesterol in blood) -> increases bad cholesterol, decreases good.
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Clinical consequences of obesity
- Hyperlipidaemia: Higher triglyceride and/or cholesterol levels
- > Diabetes associated with hypertriglyceridemia (and hypercholesterolemia)
- Consequences
- ● Insulin resistance
- ● Hepatobiliary disease
- ● Pancreatitis
- ● Ocular diseases
- ● Seizures and neurologic disorders (?)
- Hyperinsulinaemia: high levels of blood insulin
- > leads to resistance/weaker sensitivity
- > lean dogs had less insulin but are significantly more sensitive (HOMA)
- > weight loss leads to increased insulin sensitivity in cats and dogs
- Laminitis: Affliction of the hoof lamellar interface (HLI)
- > Dermoepidermal junction that serves to attach the hoof capsule to the connective tissue and the distal phalanx
- > Sinking = detached distal phalanx is forced downwards under weight to eventually compress the sole
- > Rotation = detached distal phalanx rotates and disrupts weight distribution
- > Laminitis can cause lameness and other locomotion difficulties
- Adipokines: at high levels, leptin acts as an inflammatory molecule.
- > Weight loss increases adiponectin which increases anti-inflammatory response
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Prevalence of obesity
- Dogs: 24% (1986) -> 29/34% (2006) -> ~54%
- Cats: 6/12% (1973) -> 19/25% (2005) -> ~59%
- Horses: up to 45%
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Assessing obesity
- By body weight: for dogs, >15% optimal weight HOWEVER not a great method, differences among breeds
- Body mass index (BMI): dogs (weight/height sq) accounting for breed; cats (weight/height x length); equine BMI gives range of healthy values
- Body composition: horses = use of ultrasonography to assess subcutaneous fat thickness in tail area
- Body condition score (BCS): Body score, fat coverage and ability to palpate ribs
- > scores 1-9
- > Reliable and consistent, validated by DEXA (X-ray method)
- 1 Emaciated: No discernible body fat; prominent bones; evident loss of muscle mass
- 2 Very thin: No palpable body fat; visible bones; slight loss of muscle mass
- 3 Thin: No palpable body fat; visible bones; waist and abdominal tuck are obvious
- 4 Underweight: Minimal fat over palpable ribs; waist and abdominal tuck present
- 5 Ideal: Little fat over palpable ribs; waist and abdominal tuck present
- 6 Overweight: Fat over ribs, still palpable; waist and abdominal tuck discernible from behind (w) and side (a)
- 7 Heavy: Fat covering ribs (palpable with difficulty), lumbar area and base of tail; waist and abdominal tuck not detectable
- 8 Obese: Heavy fat deposits; ribs palpable when applying pressure; no waist or abdominal tuck; abdominal distension
- 9 Grossly obese: Massive fat depots also on neck and limbs; ribs not palpable; no waist or abdominal tuck; obvious abdominal distension
- Assessing obesity in horses
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Causes of obesity
- Longer life span: easier to put on weight with age
- Neutering/Spaying: change in body composition (especially testosterone which promotes synthesis of lean mass)
- > also reduces metabolic rate
- > rapid increase in weight and blood insulin in weeks/months following neutering/spaying
- Breed disposition: particularly dogs and horses
- > dogs = Labrador, dachshunds, cocker spaniels, beagle, basset hound, shetland sheepdog
- > horses = ponies
- Owners under-recognition, Environment and Negligence: More common in pets of owners who are older or present overweight, due to
- > Low levels of exercise; Home-cooked meals; Table scraps, treats, snacks
- > More common in dogs whose owners observe them eating (psychological/behavioural)
- Environment - Thrifty gene hypothesis: horses genetically predisposed to storing energy
- > Natural selection: Metabolism optimized for native grass and long-distance travel
- > Hindgut fermentation
- > Yearly cycles of fat storage and use; Increased intake and adiposity during autumn (chronobiology adaptation); Fat stores depleted through winter
- > Neuroendocrine regulation linked to seasonal shifts in forage availability
- > Current husbandry practices: Energy-rich rations, physically inactive horses; Genetically improved grassland optimized for rapid weight gain
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Treatment
- Cats and dogs: weight loss improves respiratory function, mobility, metabolic profile and quality of life
- Gradual weight loss
- o Minimize lean tissue loss
- o Avoid weight rebound (yo-yo) effect, common in dogs
- Traditional approach: decrease intake, increase exercise
- o Low energy, high nutrient density
- o High-protein and fibre for satiety = especially in dogs; Cats -> (too much) fibre can reduce palatability; protein can increase intake
- o High micronutrient content (vitamins/minerals)
- Higher energy restriction in females
- Shift focus toward wellbeing
- Main barrier = OWNER
- > reluctance to admit to problem; lack of compliance during diet, difficulty recognising appropriate behaviour; poor cooperation of family members; inability to resist animal begging (feelings of guilt)
- Pharmacological options: amphetamines (clenbuterol, ephedrine); side effects - increased BP, temp; decreased gastrointestinal motility; tachycardia, anorexia, anxiety, death
- L-carnitine -> takes triglycerides to mitochondria for oxidisation. Evidence of effectiveness for weight loss in cats with hepatic lipidosis. Standard supplement in dogs but no research
- Orlistat -> lipase inhibitor. Side effects; steatorrhea, flatulence, discomfort, leakage
- Mitratapide, dirlotrapide (lipoprotein synthesis inhibitors) -> tops fat from being reassembled for storage. Withdrawn from market in 2010.
- Horses
- Diet: Hay as primary source of energy
- > Should be analysed for energy and nutrient content
- > Food must amount to 1.5-2% body weight
- > No grain, limited access to pasture, low-sugar, low-starch pellets treats
- > Further restriction for ponies and horses with EMS
- > Vitamin and mineral supplements required
- Increase exercise
- Pharmacological options:
- ● Levothyroxine
- ● Insulin-sensitizing drugs (metformin; safety studies lacking)
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