The "positive associative effect" of high protein
For the first time in a couple of years, the eastern twothirds of Oklahoma has substantial standing forage in many pastures as fall approaches. In addition, one can see many big round bales of hay stored for winter feed in driving around the countryside. The quality of this hay will vary a great deal. Frankly some of the hay being stored will also be less than ideal in protein content. The standing forage will be decreasing in protein content as it matures and is frosted later in the fall.
The micro-organisms in the rumen of beef cows and replacement heifers require readily-available protein to multiply and exist in large enough quantities to digest the cellulose in low quality roughages. Protein supplementation of low quality, low protein forages results in a “positive associative effect.”
This “positive associative effect” occurs as supplemental protein available to the “bugs” in the rumen allows them to grow, multiply, and digest the forage more completely and more rapidly.
Therefore the cow gets more out of the hay she consumes, she digests it more quickly and is ready to eat more hay in a shorter period of time.
Data from Oklahoma State University illustrates this (Table 1). The prairie hay used in this study was less than 5 percent crude protein. When the ration was supplemented with 1.75 lbs. of cottonseed meal, retention time of the forage was reduced 32 percent, which resulted in an increase in feed intake of 27 percent. Because hay intake was increased, the animal has a better chance of meeting both the protein and energy requirement without supplementing other feeds. Because retention time was decreased, one could postulate the protein supplementation in this situation also increased digestibility of the hay.
As producers prepare their winter supplement strategies, they can see the importance of providing enough protein in the diet of the cows to feed the “bugs” in the rumen. If the hay is low in protein (less than 8 percent crude protein), a small amount of supplemental protein such as cottonseed meal, soybean meal, or one of the higher protein by-product feeds, could increase the amount and digestibility of the hay being fed.
This strategy requires that ample forage is available to take advantage of the “positive associative effect.” As the table below illustrates, properly supplemented cows or replacement heifers will voluntarily consume about 27 percent more hay if they were provided adequate protein. As long as enough forage is available, this is a positive effect of a small amount of protein supplement. — Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist