Fatigue, feed intake focus of beta-agonist research

Fatigue, feed intake focus of beta-agonist research

The use of beta-agonists in cattle feeding is among the modern feedlot technologies making waves in the beef industry.

THE use of beta-agonists in cattle feeding is among the modern feedlot technologies making waves in the beef industry.

Kansas State University researchers, including Dan Thomson, professor and director of the Beef Cattle Institute, are among the many researchers who are examining how beta-agonists affect cattle performance and how the feed supplement might cause cattle to be slow-moving and stiff-muscled once they arrive at packing facilities, particularly in the summer months.

"We're going to learn more about the last 30 days on feed," Thomson said of research on beta-agonists. "Do we have heat stress mitigation plans in place at the feeding facilities? Are we pushing that boundary of having too-heavyweight carcasses? Are we using low-stress cattle handling techniques? How far away from the loadout facility are the fat cattle being moved? Are we shipping them during the afternoon in the heat of the day, or are we shipping them at 2 a.m.? Are the truckers trained to properly transport these animals? How long do they wait at the slaughter facility? All of these different risk factors are going to have to be bundled in."

Feedlots have used beta-agonists, a cattle feed supplement approved by the Food & Drug Administration and considered safe from a food safety perspective, to improve the cattle's natural ability to convert feed into more lean muscle.

Zilpaterol hydrochloride (Zilmax) is one of two beta-agonists approved for cattle feeding on the market. However, Merck Animal Health, manufacturer of Zilmax, voluntarily suspended sales of the product last September when major U.S. meat packers announced that they would stop buying cattle fed the product due to an animal welfare concern, which raised the question of whether the product affected the ambulatory ability, or movement, of cattle.

Thomson said because the reports of slow-moving cattle were more consistent during the summer months, he has questioned how heat stress and feeding beta-agonists might together create what he calls "cattle fatigue syndrome."

"This isn't a new phenomenon," Thomson said. "We've seen this in other species. The swine industry 15-20 years ago discovered pig fatigue syndrome. It occurred about the time they started feeding beta-agonists at a very high level to pigs. Market hogs would arrive at the plant, and they were stiff, open-mouth breathing, had blotchy skin, muscle tremors and were going through stress.

"So, these pigs show up (at the packing facility), and they don't have any clinical signs of injury besides that they don't move," Thomson said. Researchers "did diagnostic tests to look at the difference between non-ambulatory pigs and pigs within the same truckload that were able to move. They found elevated serum lactate and creatine phosphokinase (CPK) levels, which are both indicative of depletion of muscle glucose or muscle damage in these big, heavily muscled animals."

Regardless of beta-agonist use in feeding pigs, Thomson said, the swine industry went from having about a 250 lb. average out-weight to a 300 lb. average out-weight on market hogs. So, the hogs had more weight to carry around at the packing facility.

To see if beta-agonists played a role in the movement concerns, researchers did a series of tests on market hogs that were not fed beta-agonists. They put some through a stressful situation prior to shipping them to slaughter, while the others did not experience any stress.

"They were able to recreate the same syndrome that we're now seeing in some cattle," Thomson said. "Generally, physical stress — whether they were on a beta-agonist or not — showed clinical signs of fatigue in these market hogs."

Still, the swine industry has since cut the dose of beta-agonists in feeding by about 75%, Thomson said.


Cattle fatigue

The beef industry has a really good start on understanding what cattle fatigue syndrome is, Thomson said, but the reason more research must be done is that the syndrome has shown up both in cattle that were fed a beta-agonist and cattle that were not fed a beta-agonist.

"In our research, when we've looked at cattle that are not stressed and they're on one of the beta-agonists on the market, we've not seen anything but an increase in heart rate by about 10 beats per minute and no difference in lactate or CPK levels," Thomson said. "However, we have to understand that when we have seen the issues with this fatigue cattle syndrome at packing facilities, it's during the summer months, when we have heat stress."

Moving forward, Thomson said the industry needs to better understand the clinical and physiological responses of beta-agonists in cattle, if dosages in cattle feeding rations might need to be altered and if there is a potential genetic component to it as well.


Feed intake

Chris Reinhardt, feedlot specialist for Kansas State University, has looked specifically at how beta-agonists improve cattle's natural ability to convert feed into more lean muscle.

"Beta-agonists increase the deposition of lean muscle on the carcass," Reinhardt said. "They make cattle more efficient at converting grain to muscle. They also improve the efficiency of converting an animal carcass into sellable meat."

There has been no direct link established between the use of zilpaterol and impaired cattle mobility, Reinhardt said. Cattle fatigue syndrome may be caused by many factors, such as summer heat and exertion prior to harvest.

However, studying the reasons behind stiff-muscled and tired cattle and if beta-agonists play a role isn't the only angle of research being examined. Reinhardt has been looking more closely to see if beta-agonists, particularly zilpaterol, affect cattle feed intake.

"Over the past few years, on certain occasions, feedlots have seen where (zilpaterol) was started in the feed, and cattle would fall off on intake," Reinhardt said. "Sometimes, the intake would come back to normal, and sometimes, it wouldn't. Because (zilpaterol) is a growth promotant, if we're losing some of the dry matter intake and some of the energy intake, are we getting full value for that growth promotant?"

Reinhardt has looked at data from three separate commercial feedlots over the past three years and studied some of the differences in feed intake in 1,100 pens of cattle. He looked at the dry matter intake prior to and through the end of the cattle feeding period. He compared this to the time when zilpaterol was brought into the feed rations, the sex and weight of the cattle and the location of the feedlot to try to filter out any common factors when the cattle did or did not reduce feed intake.

The data analysis uncovered two main findings. First, the season played a role in the drop-off in feed intake. Second, cattle that were consuming more feed prior to the initiation of zilpaterol had a much higher likelihood of losing intake, and the size of the intake drop-off was larger.

"The drop-off was quite a bit larger in the summertime than in the other seasons," Reinhardt said. "In spring and fall, there was very little change in intake. (The pens that) did fall off on intake, for the most part, actually recovered back to normal."

Reinhardt said this could mean that weather and season, particularly heat, play a factor in cattle's response to beta-agonists. Surprisingly, the winter months showed more of a drop-off in intake overall compared to spring and fall, and Reinhardt said this issue — perhaps due to cold stress — must be looked at more closely as well.

Reinhardt said it will take more research before making specific recommendations to cattle feeders on using beta-agonists, but this initial research is one step closer to understanding how environmental factors, combined with the use of beta-agonists, might affect cattle feeding.

While Merck recently announced that it is too early to determine when zilpaterol will return to the market, many feedlots might have switched to using the other approved beta-agonist, ractopamine (Elanco's Optaflexx). The transition from one product to another hasn't been a huge challenge for many feedlot operators, Reinhardt said, but the products do work differently.


Plan progress

For its part, Merck Animal Health, with the input and oversight of its advisory board, has worked to implement its "Five-Step Plan to Ensuring Responsible Beef" and has made considerable progress, according to an announcement last month.

The findings that come as a result of the plan will add to the significant amount of data that already exist for zilpaterol, including numerous animal safety and well-being trials.

To help further ensure safe and effective product use by customers, Merck has developed a formal certification process. As part of the certification, every feedyard team member, nutritionist and veterinarian who uses zilpaterol or provides consultative services on feeding zilpaterol to cattle must be trained annually on the proper use of the product.

The training will focus on safety practices, product handling, mixing protocols, cattle management, product inventory, recordkeeping and clean-out procedures. Every certified operation will also be required to pass an initial homogeneity test to ensure proper mixing practices, as well as four additional feed mix tests throughout the year.

In addition to implementing the certification process, the company also has worked with its advisory board to develop and finalize the protocol for field evaluations for zilpaterol-fed and control cattle (previously noted as "scientific audit"), which are expected to begin in the first quarter of 2014.

The field evaluations will take place with the oversight of an independent epidemiologist and veterinarian, who will serve as principal investigator and collect all data, analyze results and publicly communicate findings in support of the company's commitment to transparency and communication.

Volume:86 Issue:03

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