Thyroxine (T4), 3,5,3'-triiodothyronine (T3), and cortisol frequently are quantified in canine serum or plasma samples to aid in the diagnosis of hypothyroidism, hypoadrenocorticism, and hyperadrenocorticism. Many laboratories have established reliable references values for concentrations of these hormones in blood of clinically normal animals. However, nonpathologic factors that affect thyroidal and adrenocortical secretion may lead to misinterpretation of test results when values for individual animals are compared with reference values. The objective of the study reported here was to identify effects of age, sex, and body size (ie, breed) on serum concentrations of T3, T4, and cortisol in dogs. Blood samples were collected from 1,074 healthy dogs, and serum concentrations of the iodothyronines and cortisol were evaluated for effects of breed/size, sex, and age. Mean (+/- SEM) serum concentration of T4 was greater in small (2.45 +/- 0.06 microgram/dl)- than in medium (1.94 +/- 0.04 microgram/dl)- or large (2.03 +/- 0.03 microgram/dl)-breed dogs, the same in females (2.11 +/- 0.04 microgram/dl) and males (2.08 +/- 0.04 microgram/dl), and greater in nursing pups (3.04 +/- 0.05 microgram/dl) than in weanling pups (1.94 +/- 0.05 microgram/dl), rapidly growing dogs (1.95 +/- 0.04 microgram/dl), and young adult (1.90 +/- 0.06 microgram/dl), middle-aged adult (1.72 +/- 0.05 microgram/dl), or old adult (1.50 +/- 0.05 microgram/dl) dogs. Dogs > 6 years old had lower mean serum T4 concentration than did dogs of all other ages, except middle-aged adults. Mean serum T3 concentration in medium-sized dogs (1.00 +/- 0.01 ng/ml) was greater than that in small (0.90 +/- 0.01 ng/ml)- and large (0.88 +/- 0.01 ng/ml)-breed dogs. Serum T3 concentration was lowest in nursing (0.85 +/- 0.01 ng/ml) and weanling (0.77 +/- 0.02 ng/ml) pups, increased in rapidly growing dogs (0.99 +/- 0.01 ng/ml) and young adult dogs (1.10 +/- 0.04 ng/ml), and decreased slightly in middle-aged (0.98 +/- 0.02 ng/ml) and old (1.01 +/- 0.03 ng/ml) adult dogs. Serum T3 concentration was unaffected by sex. Mean serum cortisol concentration was greater in small (1.06 +/- 0.07 microgram/dl)- than in large (0.79 +/- 0.03 microgram/dl)-breed dogs. Serum from nursing pups 0.57 +/- 0.04 microgram/dl) contained less cortisol than did serum from older dogs (mean values greater than or equal to 0.92 microgram/dl). Serum cortisol concentration was not different between males and females. These effects of breed/size and age on serum T3, T4, and cortisol concentrations should be considered when evaluating thyroid and adrenocortical functions in dogs.

Effects of thyroid-stimulating hormone (TSH) and thyrotropin-releasing hormone (TRH) on plasma concentrations of thyroid hormones, and effects of ACTH and dexamethasone on plasma concentrations of cortisol, were studied in adult male ferrets. Thirteen ferrets were randomly assigned to test or control groups of eight and five animals, respectively. Combined (test + control groups) mean basal plasma thyroxine (T4) values were different between the TRH (1.81 +/- 0.41 microgram/dl, mean +/- SD) and TSH (2.69 +/- 0.87 microgram/dl) experiments, which were performed 2 months apart. Plasma T4 values significantly (P < 0.05) increased as early as 2 hours (3.37 +/- 1.10 microgram/dl) and remained high until 6 hours (3.45 +/- 0.86 microgram/dl) after IV injection of 1 IU of TSH/ferret. In contrast, IV injection of 500 microgram of TRH/ferret did not induce a significant increase until 6 hours (2.75 +/- 0.79) after injection, and induced side effects of hyperventilation, salivation, vomiting, and sedation. There was no significant increase in triiodothyronine (T3) values following TSH or TRH administration. Combined mean basal plasma cortisol values were not significantly different between ACTH stimulation (1.29 +/- 0.84 microgram/dl) and dexamethasone suppression test (0.74 +/- 0.56 microgram/dl) experiments. Intravenous injection of 0.5 IU of ACTH/ferret induced a significant increase in plasma cortisol concentrations by 30 minutes (5.26 +/- 1.21 microgram/dl), which persisted until 60 minutes (5.17 +/- 1.99 microgram/dl) after injection. Plasma cortisol values significantly decreased as early as 1 hour (0.41 +/- 0.13 microgram/dl), and had further decreased by 5 hours (0.26 +/- 0.15 microgram/dl) following IV injection of 0.2 mg of dexamethasone/ferret. These results indicate that IV injection of 1 IU of TSH/ferret is preferable to IV injection of 500 microgram of TRH/ferret for thyroid function testing in adult male ferrets. Results of this study also indicated that when TRH or TSH is used for the thyroid-stimulation test in male ferrets, plasma T4 concentrations, instead of T3, should be used as the indicator of thyroid response. Additionally, IV injection of 0.5 IU of ACTH and 0.2 mg of dexamethasone may be used in ferrets for the ACTH stimulation and dexamethasone-suppression tests, respectively.

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.