Volume and Osmolality of Urine of Hypovitaminotic A Holstein Heifers

Five heifers, approximately 1 yr of age, were previously fed a vitamin A depletion ration containing 3.4% iodized salt and restricted water intake until cerebrospinal fluid pressure (CSFP) was elevated to an average of 348 mm of saline. During a 24-hr period in which no water or feed was allowed, these heifers excreted greater volumes of urine of lower osmolality than did five heifers fed the same ration plus adequate amounts of carotene and having normal CSFP's (Experiment I). The ratio of urine osmolality to serum osmolality was less in the heifers receiving no carotene. Similar results as to trend were obtained for two vitamin A-deflcient heifers of approximately 2 yr of age, when compared with two control heifers fed adequate amounts of carotene, except that the salt content of the ration for the four animals was only 0.7% and water intake was allowed ad libitum (Experiment II). In the deficient heifers on the second experiment, hemodilution, hyponatremia, and possibly hyperkalemia were accompanied by outward signs of edema. The greater urine volume and lower urine-to-serum-osmolality ratio of the deficient animals were attributed to reduced renal-concentrating capacity and impaired water homeostasis.