The weather this spring has been even more effective than usual at rearranging my travel plans. One silver lining has been plenty of airport time to get caught up on all the reading I like to do. One of the journal articles I had the chance to pull out of my “need-to-read” file really caught my attention -- enough so that I started pulling the data into some tables and charts of my own to more clearly see the story the numbers tell.
This article1 presents the results of three consecutive feeding trials done with the same group of 600-lb Holstein heifer calves and with the same fescue hay (8.7% crude protein) offered free choice as the base diet. Each experiment evaluated graded levels of a specific supplemental feed. Forage and total intake, and apparent digestibility of the ADF and NDF (fiber) and total diet, were compared between the following treatments:
Trial 1: 0.9, 1.8, 2.8, or 3.7 lb of soybean meal (a source of supplemental protein);
Trial 2: 1.5, 3, 4.5, or 6 lb of soybean hulls (a source of supplemental soluble fiber); and,
Trial 3: 1.1, 2.2, 3.3, or 4.4 lb of dry-rolled corn (a source of supplemental starch).
Strictly speaking, these results can’t be combined or directly compared for statistical analysis, because they weren’t done as a single pre-designed experiment. But because of the similarity in animals, hay, and protocol, a broad across-trial view of the results can give us an excellent illustration of the differences in animal response to protein-, fiber-, and starch-based supplements. Each of the following charts plots the responses to increasing levels of each supplemental feed, expressed as the percent increase or decrease relative to the control group, for a key indicator of diet utilization.
The two lowest levels of soybean meal, which would have delivered 0.45 and 0.9 lb of degradable protein, respectively, apparently stimulated rumen microbial activity, which in turn boosted forage intake. The higher levels of bean meal supplementation, fiber-based supplement fed above 1.5 lb per day, and starch-based feeds at any level, substituted for some of the hay the cattle would have eaten otherwise.
1 Schmidt, T.B., K.C. Olson, and M.L. Linville, “Effects of Starch, Fiber, or Protein Supplementation on Intake and Digestion of Low-Quality Tall Fescue Hay by Growing Dairy Heifers.” The Professional Animal Scientist 22:432-437, 2006.
Digestibility of the fiber portion of the diet (from hay, or, in Trial 2, from the soy hull supplement as well) was reduced an average of 7% by grain supplementation. This value understandably went up as the overall average quality of dietary fiber was increased with soy hull inclusion. Protein supplementation, up to the level that was apparently useful to the rumen microbes, had a positive impact on breakdown of the fiber supplied by the hay.
Improvements in total diet digestibility can come from two sources: substituting more highly degradable feed for a portion of the base diet, and/or improving utilization of the basal forage itself. When this chart is viewed with the previous one, it is easy to see the benefits of using supplemental feed that supports fiberdigesting microbes rather than starch-utilizers when feeding haybased diets.
If we put total intake and digestibility together, we can see the net supply of nutrients to the animal. Up to the third increment of supplementation, the level of nutrition available to the heifers receiving protein or soluble fiber supplement was very similar. Remember this represents 4.5 lb of soyhulls and just 2.8 lb of soymeal. The negative impact starch had on utilization of the hay completely offset the contribution of feeding just one pound of corn, and even the higher grain feeding rates delivered less total nutrition than the other supplements.
The results of these trials reflect and reinforce concepts that have been demonstrated in numerous other experiments. Combined, they highlight several key points to keep in mind when making supplementation choices:
- Degradable protein stimulates intake and digestion of low- and moderate-quality forages, making it an effective tool for maximizing utilization of available forage;
- Feeds high in soluble fiber, fed at several pounds daily, can substitute for (stretch) part of the forage in the diet without compromising fiber digestibility;
- Starch-based (grain) feeds are less effective for supplementing forage-based diets, as they lead to negative associative effects including reduced intake and digestion of the hay or grass.
Source: Dr. Cathy Bandyk, Quality Liquid Feeds