Supplemental Corn Silage or Baled Hay for Correction of Milk Fat Depressions Produced by Feeding Pellets as the Sole Forage

Investigated was the ability of small quantities of conventional forage to correct the milk fat depression produced when pellets are fed as the sole forage. Feeding pellets as the sole forage decreased milk fat percentage, increased milk protein and solids-not-fat percentages and had no reflect on milk production. Associated with these changes were decreases in rumen pH, protozoa numbers, and molar percentages of acetate and butyrate, whereas molar percentages of propionate and valerate were increased. Milk fat contained lowered proportions of short-chain fatty acids (C ≤ 12) and tetradecanoate, hexadecanoate, and octadecanoate; whereas, percentages of hexadecenoate, octadecenoate, octadecadienoate, and octadecatrienoate were increased. Animals which continued to receive pellets as the sole forage exhibited further alterations in the foregoing parameters, whereas supplements of corn silage (1.4 or 2.8 kg dry matter) or baled hay (2.09 kg dry matter) alleviated the milk fat depressions and caused concomitant changes in rumen chemical characteristics and fatty acid composition of milk fat. Changes in distribution of rumen volatile fatty acids were largely the result of alterations in propionate concentration. Since rumen proprionate percentages and concentrations increased, whereas percentages of milk hexadecanoate and octadecanoate decreased in conjunction with milk fat depressions and reversals were produced in these parameters as the milk fat depression was alleviated, we concluded that the major factor influencing milk fat changes was an alteration in adipose tissue metabolism probably caused by increased propionate. The increased unsaturation of milk fat produced during milk fat depressions was related to the defaunating effects of pelleted forages.