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A myth is now scientific fact


Many years ago early in my extension career, I was at a farm of a long time dairy producer. As we stood in the barn discussing feeding, cows and general dairy things, a cow near us began to urinate. The producer stopped and watched the cow urinate. When she was done, he said, "Do you know how long a cow should urinate?" Somehow, I missed that class in college and indicated I had no idea how long a cow should urinate. He said a healthy cow urinates for 20 seconds. I found this piece of information from an experienced dairy producer interesting, but not knowing what to do with it. However, over the years, I found myself watching and timing cow urinations and on average, the 20-second rule was not far off.
The urination topic came up on a farm this fall, and I repeated the 20-second rule indicating I was not sure of its validity, but it seemed like a normal time. A few days later, I saw an article by Rick Grant at the Miner Dairy Institute in NY, discussing some research he had just seen on urination time. He had recently seen an article by Georgia Tech researchers (Patricia J. Yang, Jonathan C. Pham, Jerome Choo and David L. Hu) that determined all mammals have a similar time of urination. I looked up the article on the web and there actually was some science in their research. The Georgia Tech researchers stated, "We elucidate the hydrodynamics of urination across five orders of magnitude in animal mass, from mice to elephants. Using high-speed fluid dynamics videos and flow-rate measurement at Zoo Atlanta, we discover the "Law of Urination", which states animals empty their bladders over a nearly constant average duration of 21 seconds (standard deviation 13 seconds), despite a difference in bladder volume from 100 mL to 100 L. This feat is made possible by the increasing urethra length of large animals which amplifies gravitational force and flow rate. We also demonstrate the challenges faced by the urinary system for rodents and other small mammals for which urine flow is limited to single drops. Our findings reveal the urethra evolved as a flow-enhancing device, enabling the urinary system to be scaled up without compromising its function."
So, now that we know there is some validity and rationale for a urination time of about 20 seconds, what does it mean and how do we use the information? Dr. Grant remembered reading a paper in the Journal of Dairy Science (2011; 94:4889-4896) a few years earlier by Canadian researchers who looked at when and where dairy cows defecate and urinate in a freestall barn. These researchers found most defecation and urination occurred in the feed alley or while the cows occupied a stall. Occupying a stall included lying, standing or perching (front feet in, back feet out). Frequency of urination was not correlated with feeding, milk production, stage of lactation, body weight or feed and water intake. They also found large differences in cows as to frequency of urination and defecation, but within a cow, the number of times per day a cow empties her bladder was somewhat predictable. The most predictable time for a cow to defecate and urinate is immediately following stretching as they get up from lying in a stall.
Do we need a urine scoring system? Scoring or evaluating manure is a routine practice on dairy farms and probably has a lot more significance and relationship to nutrition and health of a cow than urination time. Knowing how long it takes the average cow to empty her bladder is just one of those trivial pieces of information that is just a fun fact. Timing cow urinations, is not a measure or score that will rise to the top of our benchmarking and management data lists. The standard deviation on urination time (± 13 seconds) is more than 50 percent of the total time which means the range in urination for 66 percent of the cows is from 33 to 8 seconds. Some cows are going to urinate more and faster than others are and it has nothing to do with cow size or milk production. Urination time is not information we need to routinely record and analyze. A bit of trivia to share with someone else as you watch cows is probably all we need to do with the "Law of Urination".




 

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