Hog producers in the main hog raising states (which account for 77 percent of all hogs raised) reported 1 percent fewer pigs less than 3 months of age on their farms on March 1 than a year ago. Two percent more sows had farrowed during Decmeber - February, but heavy losses of baby pigs cut down the numbers saved.
Kutish, Francis A.
Iowa Farm Science: Vol. 16
, Article 8.
Available at: https://lib.dr.iastate.edu/farmscience/vol16/iss11/8