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Effects of Feeding Sudangrass on Iodine Metabolism of Lactating Dairy Cows¹

Animal and Range Sciences Department, Montana State University, Bozeman 59715
and Health Services Laboratory, U.S. Atomic Energy Commission, Idaho Falls, Idaho, 83401

ABSTRACT

Six lactating Holstein cows producing an average of 16 kg of milk daily were in a cross-over design of 7-day experimental and adjustment periods. Cows were fed either sudangrass or bromegrass green chop ad libitum as the only forage. Each cow was dosed orally with 120 µCi ¹²⁵I and 500 µCi ¹³¹I at the beginning of the first and second experimental periods, respectively. Cows were in metabolism stalls and blood, feces, urine, and milk samples were collected for 7 days post-dosing. Average 7-day excretions of radioiodine doses by cows on sudangrass and bromegrass treatments were 4.5 and 8.3% (P < .025) in milk, 36.8 and 35.5% (P > .10) in feces, and 39.7 and 34.3% (P > .10) in urine. Plasma radioiodine did not differ (P < .05). Feeding sudangrass reduced the average percentage of the total radioiodine dose secreted (in 7 days) per kilogram of milk from .090 to .048 (P < .01) and the milk:plasma ratios from 2.05 to 1.01 (P < .05).

¹ Contribution from the Montana Agricultural Experiment Station Journal Series 309.

² Present address, Division of Compliance, U.S. Atomic Energy Commission, Washington, D.C. 20545.

³ Present address, Coon Rapids, Iowa.