Volume and Osmolality of Urine of Hypovitaminotic A Holstein Heifers

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Abstract
In the first experiment 5 heifers, approximately 1 year of age, were given a vitamin A depletion ration containing 3.4% iodized salt and restricted water until cerebrospinal fluid pressure (CSFP) was elevated to an average of 348 mm of saline. During a 24-hour period in which no water or feed was allowed, these heifers excreted greater volumes of urine of lower osmolality than did 5 heifers fed the same ration plus adequate amounts of carotene and having "normal" CSFP''s. The ratio of urine osmolality to serum osmolality was less in the heifers receiving no carotene. In a second experiment a similar trend was observed for 2 vitamin A-deficient heifers of approximately 2 years of age when compared with 2 control heifers fed adequate amounts of carotene; however, the salt content of the ration for the 4 animals was only 0.7% and water intake was allowed ad libitum. In the deficient heifers, hemodilution, hyponatremia, andpossiblyhyperkalemia 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.