Rumen Response to Cold Water
While reading articles describing "normal" body temperature I ran across an article that investigated the effects of feeding various temperature water to calves. "Temperature change within the rumen, crop area, and rectal area when liquid of various temperatures was fed to calves." [Dracy, A. E. and A.J. Kurtenbach, Journal of Dairy Science, Vol 51, No. 11, pp 1787-1790.]
The colder the water the larger the drop in ruminal fluid temperature. That was obvious before doing the measurements. But, how large is the decrease? When about 2 quarts of 46F water was fed the rumen contents plummeted from 104F to 84F. It took about 30 minutes for these rumen contents to get back up to about 100F and a full hour to reach the original 104F.
Why so long to rebound? Well, think about what happens to microbial activity with the temperature drops 20 degrees. Activity slows a lot. When this occurs heat being generated by microbial fermentation goes down. Thus, rather than warming from the inside (microbial fermentation) the contents have to draw heat from the body core.
As the calf recovers from this temperature shock the rumen fermentation will pick up speed and get back to normal. However, we did divert energy from growth with this cold water and we sacrificed roughly 10 to-15 percent of her fermentation time to the recovery phase [time estimate mine, not from research].
The authors also investigated the effects of volume on temperature shock. Using 63F water they fed various volumes ranging from 1.8 quarts to 3.5 quarts (these are about 8 week-old calves not yet weaned). The smaller volume of water depressed rumen temperature to about 92F compared to the larger amount pushing rumen contents temperature to 87F. These may be compared to normal rumen temperature of these calves of 104F.
Another research team followed a similar water feeding protocol with lactating cows. When fed 46F water the rumen temperature drop was about 15 degrees, when fed 94F water the same drop was only 4 degrees. The animals drinking the 46F water took about 2 hours to get back to "normal" temperature for rumen contents. [Bewley, J.M et al., "Impact of water intake temperature on reticular temperatures of lactating dairy cows." Journal of Dairy Science vol 91, pp 3880-3887.]
The point of all this discussion is our management decision about what temperature water to feed calves, especially those old enough to have significant rumen microbial fermentation. The closer the water temperature is to calf body temperature the less the negative consequences for rumen fermentation.
And, based on my observations, calves like to drink warm water better than cold water so they drink more. The more water they drink, usually the more calf starter grain they will consume.