How Nutrition Affects the Beef You Sell and the Manure You Haul

Dr. Steven C. Loerch

The Ohio State University

 Introduction

             Crop production captures energy and nutrients from sun and soil over an extensive land mass.  Expansion and consolidation of the cattle feeding industry concentrates these nutrients in a relatively small area.  This results in an uncoupling of livestock production from crop production.  In other words, more nutrients are imported to the feedlot and less manure is distributed back to the land that produced these nutrients.  The primary nutrients of concern are nitrogen (N) and phosphorous (P).  This paper will discuss how cattle nutrition affects the generation of manure, N, and P in the feedlot.  In addition to nutrients not captured in animal products, nutrition affects the composition and characteristics of the beef produced.  Value based marketing of cattle dictates that carcass characteristics play a bigger roll in determining profitability.  This paper will discuss how nutritional strategies affect carcass characteristics that drive profitability.

 Nutrient Balance Challenge

             Nutrient balance means that the importation of nutrients is in balance with the removal of nutrients on a given area of land.  This is a challenge for cattle feeders for two reasons.  First, cattle are not efficient in capturing nutrients in animal products (i.e. carcass beef).  Typically, cattle diets are 60-90% digestible.  This means 10-40% of every pound they eat is deposited back on the pen surface.  Only 30% of the N and 15% of the P cattle consume are retained in the animal.  The balance is excreted.  The second nutrient balance challenge for cattle feeder’s deals with the uncoupling of grain and beef production.  A good example of this involves the grain processing industry.  A typical ethanol plant will draw corn from a radius of more than 200 miles.  To be profitable, wet distillers grains are marketed through livestock located within 20 miles of the ethanol plant.  Ethanol does not contain N or P.  Therefore, all the N and P in corn, produced over a large land mass, ends up being fed to cattle produced on a much smaller land mass.  The end users of the nutrients (cattle feeders) get blamed if water and air pollution result.

 Nitrogen

             One thousand feedlot calves will eat about 475 lbs of N/day.  Of this, only 140 lbs will be retained in the cattle, while 335 lbs will be excreted.  Consider the fate of N for a calf eating 1,000 grams of protein a day.  Only 30% of the N in that 1000 grams is captured by the animal.  Fifty percent of the N consumed is excreted in the urine and 20% of the N consumed ends up in feces.  This is not an efficient process and the story gets worse.  Of the urinary N excreted, 97% is volatilized and is lost to the atmosphere as ammonia.  About 50% of fecal N volatilizes.  Bottom line is that 85% of the N excreted by a feedlot calf ends up in the air.  Historically, this has not been a big problem.  However, regulations are changing.  The EPA published new air quality standards in 1997.  These standards are designed to regulate particles in the air that are greater than 2.5 microns (the old standard was set at 15 microns).  Ammonia reacts with other compounds in the atmosphere and forms particles greater than 2.5 microns.  Therefore, ammonia is considered a “Criteria Pollutant” for air particle pollution control strategies.  Nitrogen compounds in the air have been blamed for increasing acid rain, increasing smog, increasing greenhouse gases and changing aquatic plant and animal ecosystems.

 The EPA has estimated that 43% of atmospheric ammonia comes from cattle, so this is a problem we still have to address in the near future.  Currently, there is no silver bullet to solve the problem but there are actions that can have an impact.  The most effective strategy is to work with your nutritionist to avoid over-feeding protein.  Currently, it is pretty cheap to over feed protein as an insurance factor.  The reality is that 85% of all protein fed in excess of the requirement for microbes and cattle gain ends up as a pollutant.  Protein intake should be matched with the animal’s requirements.  If you feed the same protein supplement (at the same inclusion rate) throughout the feeding period, this isn’t happening.  Frequent feed testing is also necessary to avoid over feeding protein.  Designing supplements to meet microbial and animal requirements (metabolizable protein) will reduce N losses.  Use of lean growth promotants (like implants) increase the capture of N in the animal.  Research efforts are underway throughout the U.S. to reduce volatilization of ammonia from manure.  This may be feasible in the future.  Corn plants require a N:P ratio of about 5:1.  This is the ratio found in fresh manure.  However, stored manure has a N:P ratio of about 1:1.  Capture of more excreted N within manure would improve its usefulness as a fertilizer.

 Phosphorus

             Regulations based on P standards are becoming more common.  Phosphorus based application standards will dramatically increase the land base required for manure disposal.  The NRC says that cattle require only .25% P in the diet.  Even better news is that recent Nebraska research indicates the P requirement may be as low as .16% of the diet.  Unfortunately, cattle are typically fed twice this level.  Corn grain contains about .35% P.  Byproducts (gluten feed, distiller’s grain, and soybean meal) contain more than .7% P.  It is impossible to formulate a practical diet that does not exceed cattle P requirements.  Fortunately P is easier to control than N because it doesn’t volatilize.  Manure management strategies to control run-off and ground water contamination are effective.  You and your nutritionist have slim options when it comes to P.  One thing you can do is make sure mineral supplements do not contain supplemental P.  Plant genetic engineering may reduce P content of our feeds in the future, which would be a big help.

 Manure Output

             Total manure output by a feedlot calf is a direct relationship between feed intake and the indigestibility of the diet.  A calf eating 20 lbs of a 60% digestible diet will produce 8 lbs of manure dry matter (24 lbs on a wet basis).  If diet digestibility is 90%, then DM manure output will only be 2 lbs/d (10 lbs on a wet basis).  Any time forage is added to a ration, manure output will increase.  This should be kept in mind as growing programs are being contemplated.  If you want to reduce manure output in a backgrounding or growing program, the best way to accomplish this is by limit-feeding a high grain ration.  Feeding 20 lbs of a hay-based diet may allow a calf to gain 1.5 lbs/day but it will generate 20 lbs of manure.  Limit-feeding a 90% grain diet can result in the same gain (with 9 lbs of feed) but manure output will only be 5 lbs/day.  Table 1 describes this principal for calves at three projected growth rates with three types of feed.  In most of our limit-feeding programs I advocate feeding corn whole to delay fermentation rate in these cattle.  In fact, there are many instances when feeding corn whole should be considered.  Whole corn reduces off-feed problems when starting calves and for calves that will be on feed for long periods (more than 160 days).  We found the advantages of grinding corn diminish, the longer cattle are on feed.  In fact, for cattle on feed for 185 days, those fed whole corn gained faster and more efficiently than those fed cracked corn (Figures 1 and 2).  We also conducted a digestion trial so we could measure just how many whole corn kernels appeared in the manure.  Results are in Table 2.  Starch digestibility was not affected by corn processing.  Calves ate about 38,000 kernels of corn/day and excreted about 500 whole kernels in the manure.  More than 95% of kernels were broken down in the digestive tract.  Starch analysis of “whole” kernels revealed some starch loss even though kernels appear intact.  If you have cattle on a “natural” program (no ionophores or antibiotics), feeding corn whole may reduce fluctuations in feed intake as well as metabolic and liver abscess problems.

 Nutrition and Carcass Characteristics

             At a given base price, carcass value is determined by weight, quality and yield.  Nutrition affects all three.  The most revealing example of this is to consider Holstein steers.  If you put Holstein steers on feed weighing 350 lbs and feed them hard, typically more than 80% of them will grade Choice with less than .3 inches of backfat at 1250 lbs.  If you feed forage to those 350 lb Holsteins until they weigh 800 lbs and then feed them hard, less than 50% of them will grade Choice when they reach .3 inches of backfat weighing 1700 lbs.  Holstein data and the more recent early-weaning work with beef cattle at Ohio State and Illinois reveal that early calf nutrition affects maintenance energy requirements and the initiation of marbling.  We used to believe marbling took place at the end of the feeding period and after backfat deposition was well along.  We now know this is not the case.  Fat cells are capable of rapid multiplication when the calf is 4-9 months of age.  These cells provide the framework for fat deposition later in life.  For years the beef industry has struggled with the fattening dilemma.  We want cattle to get fat, but only in one place (in the muscle)!  This is contradictory to the growth process.  We know genetics plays a role in partitioning fat accretion between the subcutaneous and intramuscular depots.  However, nutrition and management also offer opportunities.  Energy amount and source influence fat cell development and marbling potential.  Placing calves on a high grain diet at or before 7 months of age greatly increases marbling scores at a given backfat.  Recent implant research at South Dakota State revealed that androgenic implants have a bigger effect on marbling early in the feeding period, rather than later.  That 500 lb calf we typically would discount for carrying too much flesh (due to creep feeding or early grain feeding) will actually be the calf most likely to grade when it is finished.  There are a couple of nutrition principles we may be able to capitalize on to influence the fattening process.  The first one revolves around source of energy.  The  major VFA end product of fiber fermentation is acetate.  Acetate is the major building block of fat synthesis in the subcutaneous depot.  The major acid end products of starch fermentation are propionate and lactate.  These acids are gluconeogenic meaning the animal makes blood glucose from them.  This also increases insulin output. 

             Propionate and lactate provide the majority of carbon skeleton building blocks for fat synthesis in the intramuscular depot.  Another nutrient that may play a role in this process is Vitamin A.  High levels of Vitamin A inhibit fat cell multiplication.  The Japanese have discovered cattle with high blood vitamin A have lower marbling scores; low blood vitamin A correlated with high marbling scores.  Forages are a great source of carotene (a Vitamin A precursor).  High Vitamin A status in calves up to 10 months of age may decrease fat cell multiplication and inhibit their ability to marble.  Feedlot diets typically contain more than twice NRC requirements for Vitamin A.  It’s not known what affect this might have on carcass quality.  Ohio State’s Beef Research team is currently pursuing this question.

Tables and Graphs