Agricultural engineers at Iowa State Colle have developed a continuously circulating hog watering system. It eliminates the need for individual heating units in the waterers to prevent winter freeze-ups.
Hazen, T. E. and Curry, N. H.
"Develop New Hog Watering System,"
Iowa Farm Science: Vol. 13
, Article 4.
Available at: https://lib.dr.iastate.edu/farmscience/vol13/iss6/4