Genetic selection for improved production in dairy cows also has resulted in parallel growth in body frame over the years. The average body weight of Holstein cows at a Wisconsin dairy show in 1917 was 1,225 pounds, according to University of Nebraska researchers who recorded the weights. The average cow weight nowadays is close to 1,500 pounds, with some cows well above that scale measurement.
Milk production for these 1917-version cows averaged 14,712 pounds. Meanwhile, it is not unusual to find well-managed farms with a rolling herd average of 36,000 pounds today. While body weight has climbed by 22.4%, milk production has leapfrogged by 146%! These large volumes of milk require higher nutrient uptake which cows can accomplish by better feed selection, greater intakes, and improved digestibility.
In confinement dairy systems, feed selection is limited, with nutrient uptake being determined by diet digestibility and individual intake. There is an upper limit to which nutritionists and feeders can improve diet digestibility before digestive upsets occur; any additional nutrient demands need to occur through increased feed intake. The paradigm, though, is that as feed intake climbs, so does passage rate. That, in turn, reduces digestibility. One approach that has been used to improve the digestibility of the forages fed is the addition of exogenous enzymes.
Results in the cow
Research results using these enzymes, however, have not always been consistent. Depending on the substrate, the terms include amy lases, cellulases, β-glucanases, hemicellulases, xylanases, pectin ases, and proteases. Some of these enzymes are synthetized by fungus of the genus Aspergillus. Aspergillus oryzae alone, or in combination with A. niger, produce cellulases, pectin ases, and amylases. The means of action is by a synergism between these fungus and rumen microbes enhancing the release of plant cells nutrients in the rumen.
Continue reading this article published in Hoard’s Dairyman.
