Effects of particle size and formaldehyde treatment of soybean meal on milk production and composition for dairy cows.

Twenty-four lactating dairy cattle were used to study the effects of formaldehyde treatment and reduction of particle size of soybean meal on milk production and composition. Cows were fed diets containing one of the following soybean meals: 1) untreated, coarse; 2) untreated, fine; 3) formaldehyde-treated, fine. Formaldehyde reduced the solubility of soybean meal protein from 22.7 to 2.9%. Grinding soybean meal reduced particle size from 842 to 249 micron. Formaldehyde treatment did not affect intake or milk production but resulted in higher efficiency of milk production (1.43 versus 1.46 kg fat-corrected milk/kg dry matter intake). Milk protein (3.08 versus 2.85%) and solids-not-fat (8.51 versus 8.35%) contents were reduced by formaldehyde. Cows fed fine soybean meal had higher dry matter intakes (22.0 versus 20.8 kg dry matter/day) and gained more body weight; however, milk production was not affected by particle size. Grinding soybean meal reduced production efficiency (1.47 versus 1.42 kg milk/kg dry matter intake) and milk fat (3.70 versus 3.33%). Lack of production response and reduced milk protein from formaldehyde treatment suggests possible overprotection of protein. Fine grinding of soybean meal appeared to favor body weight gain rather than milk production.