A 10-week-old, singly-housed female spontaneous dwarf rat weighing 50 g was presented for physical examination because of abdominal distension and icterus. The animal was a member of a breeding colony of approximately 50 spontaneous dwarf rats (Rattusnorvegicus). Spontaneous dwarf rats are homozygous for the autosomal recessive mutation in the growth hormone gene, which results in complete, isolated growth hormone deficiency. Spontaneous dwarf rats are a unique model for the study of pituitary-regulated fetal and post-natal growth, including investigation of the genetic mechanisms and endocrinology of dwarfism. The colony was originally isolated from a closed colony of Sprague Dawley rats in 1977 (1-4). Animals were housed in filtertop cages on hardwood chip bedding (Sam-Chip; P.J. Murphy Forest Products, Montville, N.J.). Each cage had a bottle source of reverse osmosis water and ad libitum rodent chow (22/5 Eodent Diet; Harlan Teklad, Madison, Wis.). Room temperature was kept between 21 and 23.5°C, and the room was ventilated with >20 air exchanges/h. The light cycle for the room was activated between 0700 and 1900. In addition to the findings of abdominal distension and icterus, the physical examination revealed hypothermia (rectal temperature of 35°C, reference range 36 to 37.5°C), respiratory rate of >100 breaths/min with no auscultated lung field abnormalities, and pale mucous membrane and pinnae coloration. Abdominal palpation revealed indistinct abdominal viscera and fluctuation. Theanimal's body condition was poor in comparison with age- and sex-matched littermates weighing 60 g.
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