Serum lipoprotein concentrations, routine serum biochemical values, and morphologic changes of the liver were evaluated in cats undergoing weight loss. Food was withheld from 6 obese and 6 control cats for 3 days (days 0 to 2), followed by feeding 50% of previous food intake for 26 days (days 3 to 28). Percutaneous liver biopsy specimens were obtained from all cats on days 0, 7, 14, and 28. Blood samples for serum biochemical analysis and lipoprotein profiles were obtained on days 0, 3, 7, 14, and 28. All cats lost weight throughout the study, and none developed signs of chemical illness, including those of idiopathic hepatic lipidosis syndrome. Serum total cholesterol concentrations decreased initially in all cats, but rapidly returned to normal after day 3 in obese cats, suggesting altered cholesterol metabolism during dietary restriction. Low-density lipoprotein concentrations decreased throughout the study in control cats, but were unchanged in obese cats. Examination of liver biopsy specimens from each cat revealed minimal lipid accumulation in all specimens, although some specimens contained hydropic degeneration.

The effect of furosemide-induced weight loss on the energetic responses of horses to running was examined in a 3-way crossover study. Eight 2- to 3-year-old Standardbred mares received, in random order, 10 ml of saline solution 4 hours before running on a treadmill (control trial, C); or, during 2 trials, 1 mg of furosemide/kg of body weight, IV, 4 hours before running. During one of the trials when the horses received furosemide, they carried weight equal to that lost over the 3.75 hours after furosemide administration while running (furosemide-loaded, FL), and during the other trial they did not carry weight equal to that lost after furosemide administration (furosemide-unloaded, FU). Horses performed an incremental exercise test on a treadmill during which rates of oxygen consumption (V(O2)) and carbon dioxide production (V(CO2)) were measured, respiratory exchange ratio was calculated, and blood samples were collected for determination of mixed venous plasma lactate concentration and arterial and mixed venous oxygen saturation. Furosemide treatment caused significantly (P < .001) greater weight loss than did saline administration; mean +/- SEM weight loss (exclusive of fecal loss) was 1.6, 8.8, and 10.2 kg (SEM = 2.0) for C, FL, and FU trials, respectively. The speed at which peak V(O2) was achieved was 9.31, 9.56, and 9.50 (SEM = 0.16) m/s, respectively, time to fatigue was 547, 544, and 553 (SEM = 26) seconds, respectively, and the highest speed attained was 10.3, 10.2, and 10.2 (SEM = 0.2) m/s, respectively. Mean peak rate of oxygen consumption was 130.7, 129.6, and 129.6 (SEM = 1.9) ml/min/kg, respectively. There was a significant (P = 0.070) group X speed interaction for V(CO2); during trial FU, horses had significantly (P < 0.05) lower rate of CO2 production at speed of 9 m/s and at the speed that caused peak V(O2), than during trial C. The respiratory exchange ratio during the FU trial was significantly (P < 0.05) less than that during the C trial at the speed that caused peak V(O2). Plasma lactate concentration at speed of 9 m/s for C, FL, and FU trials was 15.4, 16.5, and 13.3 (SEM = 0.8) mmol/L, respectively; values for the FL and C trials were not significantly different, whereas the mean value for the FU trial was significantly (P < 0.05) less than that for the C trial. Thus, administration of furosemide to horses altered the energetic response to exertion. Replacement of the furosemide-induced weight loss resulted in V(CO2), plasma lactate, and respiratory exchange values indistinguishable from those during the control trial.

Two experiments were conducted to determine changes in body composition and various physiologic variables in feeder pigs under simulated marketing conditions. In the first experiment, pigs were assigned to 1 of 4 treatment groups for 48 hours: (1) no water and feed; (2) water ad libitum, no feed; (3) no water, feed ad libitum; or (4) water and feed ad libitum. During a 48-hour recovery period, all pigs were allowed feed and water ad libitum. Plasma triiodothyronine decreased (P < 0.01) within the first 24 hours in groups-1 and -2 pigs, but increased (P < 0.01) within the first 6 hours of the recovery period. The circadian rhythm of plasma cortisol was disrupted in groups-1 and -3 pigs and during recovery in group-1 pigs. Packed cell volume increased (P < 0.05) in groups-1 and -3 pigs and returned to initial values within the first 24 hours of the recovery period. In the second experiment, body composition was estimated by the 40K technique for fat-free body mass, percentage of nitrogen, and percentage of fat. Body composition was determined before and after pigs were allotted to 1 of 2 groups for 48 hours: group-1 pigs were given feed and water ad libitum and group-2 pigs were not given feed and water. Group-1 pigs gained 2.2 kg of body weight (P < 0.01), 0.6% fat (P < 0.01), 0.7 kg of fat-free body mass, and 0.02% nitrogen (P > 0.01). Group-2 pigs lost 2.3 kg of body weight (P < 0.01), 0.6% fat (P < 0.01), 2.0 kg of fat-free body mass (P < 0.01), and 0% nitrogen.