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Update on Nutrient Requirements of Dairy Cattle revision process

Carl Old Published on 06 November 2014

It should be obvious that nutrient requirements of dairy cattle are the same as they have always been; we are the ones slowly advancing our understanding of those requirements.

The purpose of the various editions of the National Academy of Science/National Research Council publication on the nutrient requirements of dairy cattle is simple. Users of that system must be able to predict how cattle will perform for a given set of inputs and able to predict what those inputs should be for a given output.

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In the statement of task, the committee is charged with the evaluation of “… new information in order to improve accuracy of prediction of animal performance from nutrient input and vice versa as well as enhance nutrient utilization.”

For example, if it is decided that Holstein heifers weighing 300 pounds should gain a certain amount per day, feeding standards give guidelines as to the combination of feeds that will produce optimal results. On the other hand, if those calves are fed a given blend of feeds, how accurately is the actual performance predicted?

The first publication “Recommended Nutritional Allowances for Dairy Cattle” was released in 1945 and was a TDN-based (total digestible nutrients) system. While Europeans were using net energy values for feeds before that time, it was 20-plus years later that we finally adopted energy-based feeding standards for both dairy and beef cattle.

The seventh revised edition was published in 2001; since that time, new information on various aspects of dairy cattle nutrition has been published. Some of these are ways in which to reduce methane and other emissions from dairy cattle, increased use of byproducts (especially those from fuel alcohol production) and an increased awareness of the effects of beneficial bacteria (probiotics) on overall animal health.

The American Dairy Science Association (ADSA) played an important role in helping to raise the $400,000 needed to get the ball rolling on the new dairy nutrient requirements. The ADSA pledged $204,000 in funding and began a fund-raising campaign for the additional $196,000.

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Shortly thereafter, the following co-sponsors were announced: Ajinomoto-Heartland, BASF, Cargill Animal Nutrition, Elanco, Evonik Industries AG, Hubbard Feeds, IFEEDER (Institute for Feed Education and Research), Innovation Center for U.S. Dairy, Kemin Industries and Novus International.

First and foremost, the committee is charged with improving accuracy of prediction of animal performance from nutrient inputs and vice versa. If enough new information is available, an update of the current feeding standard may be developed. New ideas must have biological meaning and should not be introduced simply because they are novel.

Current energy-based feeding standards, for dairy and beef, are empirical – that is, they are based on observation and may not be based on the underlying biological mechanisms. The new committee is charged with placing special emphasis on biologically relevant estimates of energy utilization for maintenance, milk production, lean and fat gain in growing and lactating animals, and gains during pregnancy.

It is thought that doing so will allow for increased accuracy of prediction and enhanced nutrient utilization throughout the life cycle of our cattle. If this works as planned, we can feed less and get more for it.

The vast majority of dairy cattle in the U.S. are fed in drylot; however, grazing systems have become more popular in the last 20 years. A section of the new document will be devoted to a summary of pasture and grazing research.

In that light, it is interesting to note comments made more than 20 years ago by New Zealanders Mark Ulyatt and Garry Waghorn. In the middle of the last century, milk production per cow was similar in the U.S. and New Zealand.

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From that time until the 1990s, the rate of increase in milk production in New Zealand was 25 percent of that in the U.S. Ulyatt and Waghorn stated that increased production in their country was mainly due to improved genetics, and much of the increased production in our country was due to improved nutrition.

According to Ulyatt and Waghorn, “Producers in the U.S. have captured and exploited the results of 40 years’ research in ruminant nutrition: We have not because we are trapped in our pasture-based system.” They further state, “We come to the inevitable conclusion that we starve our cows in New Zealand.” Maybe the committee can get some ideas on pasture from these guys.

An entire book could be written on nutrients needed for optimal performance at any one stage in the life cycle; the committee will review nutrients needed by bottle calves, weaned calves, growing and breeding heifers, milking and dry cows.

It is important to supply nutrients needed by an animal for a given function in a form that results in maximum efficiency. If you’ve ever framed a building, you know that it’s a more efficient use of time to use a stud-length two-by-four than to cut random-length two-by-fours to the appropriate length.

An example of this in lactating cows is how the “metabolic decisions” made by those cows affect efficiency. When fat is fed (assuming it is the right kind), it may be incorporated into butterfat with an efficiency of greater than 90 percent.

If, on the other hand, fat is made from the simplest building blocks, the efficiency is much less; estimates of efficiency have been calculated to be around 70 percent. For a group of cows producing 75 pounds of milk with a butterfat of 3.5 percent, the less efficient pathway means 1.5 pounds more dry matter is required to produce the same amount of milk component.

This example assumes that half of milkfat is made in the udder and half is delivered to the udder from blood. The waste stream is reduced by more than 100 tons per year for a 1,500-cow dairy, and methane emissions are reduced as well. Information of this type, for all stages in the life of dairy cattle, will allow for either increased production using no more feed than we use today or maintaining production with fewer inputs.

Most computer models used to formulate and evaluate rations assume linearity – that is, 1+1 = 2. Only a few cows, if any, attended school, so they are unaware of this fact. A lot of cows tell us that in many cases 1+1 does not equal 2; it may be 1 and it may be 4. This is not a new finding; it was reported on in 1937.

While we assume that the energy value of a feed is constant, it may vary. Rations that are nutritively complete are utilized more efficiently than those with deficiencies. Corn has a net energy value greater than that of alfalfa hay, but when fed with alfalfa hay, fattening cattle perform better than those fed just corn.

Again, 1+1 doesn’t always equal 2, a point that should be taken to heart by those who formulate rations for all classes of livestock. This is a difficult concept to mold into systems that are inherently linear (LP does mean linear program) but also points out that regardless of what the academicians come up with for recommendations, there will always be some room for “art” in ration formulations.

The statement of task also requires that a sensitivity analysis of the model be provided. Sensitivity analyses are performed to evaluate changes in model output as a function of changes in model input.

Researchers in 2007 examined two models for inputs soluble carbohydrate, starch, crude protein, soluble crude protein, neutral detergent fiber, acid detergent fiber, lignin, ether extract, lysine and methionine. The authors changed input of each of these by 20 percent more or less than baseline values.

Of the 10 inputs examined, variation in only three – crude protein, soluble crude protein and neutral detergent fiber – were of importance in predicting change in model output. This is not to say that actual milk production would be different, just that the models did not predict it.

Remember, the cows will show us what their nutrient requirements are; we’re making SWAGs, and that’s not “stuff we all get.” While it’s not likely to happen, a few cow trials evaluating any new recommendations would boost credibility for the upcoming dairy NRC.

It’s not known when the new recommendations will be published; one can only hope that the work of this committee will allow for improved efficiency of feed energy utilization in all classes of dairy cattle. PD

Carl Old is a nutritionist from LeGrand, California.

References omitted due to space but are available upon request. Click here to email an editor.

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