Losses can occur from sickness, excessive stress, weather events, individual genetic anomalies, management and handling, equipment and facility misuse or misdesign, and any combination of these.

In general, the greatest cause of death loss in the feedyard is related to bovine respiratory disease (BRD) and occurs in cattle shortly after they arrive at the facility.

With cattle-feeding operations (but not only in cattle-feeding operations) an ongoing and significant source of losses is linked to nutrition and feeding problems that occur in the rumen of the animal (digestive upsets). In most cases, this is directly related to feeding high-grain (high-starch) diets to an animal that is really not designed to consume diets of this type.

Virtually all cattle start off on pasture and high-forage diets. At some point, as calves are weaned and grown they will be moved onto diets that are higher in energy to facilitate finishing. As anyone who has fed cattle knows, this means moving them from a high-fiber diet to a high-grain diet (generally corn, but this may vary depending on location).

While losses due to BRD occur early in the feeding period, digestive issues most often develop after the animal has been on feed for some period of time. In a 2015 study by Vogel et al., researchers found, on average, respiratory disease-related cattle deaths occurred at about 62 days on feed, while digestive-related losses occurred at an average of about 99 days on feed. A significant implication is that the digestive-related cattle deaths occur after the animal is larger and has consumed more feed. Thus, the animal is more valuable and more expense has accumulated. A loss at this stage is very costly.

Cattle have been fed high-grain diets in confinement for decades, so the reality of cattle losses from digestive issues is nothing new. Additionally, as a review of production databases have shown, losses due to digestive issues have actually increased over recent years, despite the fact that the industry understands the etiology of the various conditions.

To review

There are four major metabolic, rumen-based conditions that lead to the majority of the death loss. These include:

Acidosis

Acidosis occurs when the contents of the rumen, and subsequently the blood, become acidic. It is caused by two primary factors: excess organic acid production in the rumen and decreased buffering of the rumen digesta as a result of decreased saliva production which comes with consumption of high concentrate diets. Saliva contains large amounts of sodium bicarbonate, which is a buffer that neutralizes acids.

Acids in the rumen are produced by rumen bacteria during the fermentation of feed, particularly grains and starch. These acids are absorbed and provide the major source of energy to cattle. Two “degrees” of acidosis occur; acute acidosis and subacute or chronic acidosis. Acute acidosis usually occurs when cattle not adapted to high grain levels are given access to a large quantity of grain. This results in a rapid drop in rumen and blood pH, which can cause sudden death.

Subacute acidosis is more common in feedlot cattle and is more costly to the producer. Subacute acidosis occurs when cattle fed high-grain diets are not able to balance acid production with the buffering capabilities of saliva. Cattle normally produce 5 to 10 gallons of saliva daily.

Most of this saliva enters the rumen during rumination, the cud-chewing process. When finishing diets low in roughage are fed, cattle do not ruminate normally, don’t regurgitate a fiber “bolus,” effectively reducing saliva flow and buffering capacity. Subacute acidosis depresses pH less but still is harmful to normal rumen function.

Grain bloat

A typical result of ruminal fermentation is gas production. In normal situations, cattle are able to belch (eructate) and release excessive gas. Feedlot bloat is not caused by increased gas production, but rather, the inability to release gas by belching. Consumption of finely ground feeds promotes foaming or frothiness in the rumen.

This foam or froth has a high surface tension, and the gasses are trapped in the foam and belching is prevented. High-grain diets also promote the growth of certain rumen bacteria which produce a slimy matrix which traps gasses. Additionally, acidic conditions in the rumen stabilize the foam. Saliva contains antifoaming agents, but as discussed above, saliva production is greatly reduced on high-grain diets. The rumen becomes so distended that the animal can no longer breathe and death is caused by asphyxiation.

Polioencephalomacia (PEM, polio)

This condition is an acute deficiency of the B vitamin thiamin. Thiamin is required for energy metabolism. When deficient, the animal’s brain is essentially starved of energy. Normally, rumen microbes synthesize all the B vitamins needed, so none have to be provided in the diet.

Overall, about 1% of feedlot cattle develop PEM. The disease is unpredictable and a feedlot may go several years without incidents, only to have several cases in a single group of cattle. Again, occurrence is associated with high-grain feeding and usually occurs shortly after switching cattle to their finishing diets. At this point, rumen microbes are adjusting to the new feed, and acidosis is not uncommon.

It is believed that certain bacteria in the rumen produce thiaminase, an enzyme that destroys thiamin and produces thiaminlike compounds which block the action of the true vitamin. Cattle affected by polio have normal thiamin production, but it is being destroyed before the animal can use it.

Symptoms include listlessness, incoordination and convulsions. Death occurs rapidly if cattle are not treated. However, treatment is simple and results in rapid recovery. Afflicted cattle should be given an IV injection of thiamin solution (2 grams for a 700-pound calf) two times per day for two days. Methods of reducing acidosis are beneficial in preventing polio, as they are related.

Rumenitis

Rumenitis is an inflammation or irritation of the rumen wall. It is caused by long-term feeding of high-grain diets, which results in continuous acidic conditions and lack of physical stimulation normally caused by larger fiber particles (scratch factor). Like acidosis, a low level of rumenitis is common when high-grain diets are fed.

The problem worsens the longer cattle are on the finishing diet. When condition becomes severe, the lining of the rumen wall becomes ulcerated and is no longer functional and effective in absorbing nutrients. A result is cattle stop growing toward the end of the feeding period (plateauing or stagnating). Another result is liver abscesses. When ulcers develop, certain ruminal bacteria pass into the blood, travel to the liver and cause abscesses.

Interestingly under most conditions, only cattle with severe liver abscesses have reduced performance. Feeding antibiotics such as tylosin or chlortetracycline have been shown to reduce the incidence of liver abscesses. They do not prevent rumenitis, however.

All of these conditions develop as a result of feeding a high-grain, high-starch diet that reduces the pH of the rumen. The cattle feeder must always balance this high-acid production and excessive rumen acidity that develops from the feeding of high-grain diets necessary to maximize performance and economic returns.

Some solutions that have developed over the years include the feeding of ionophores. These compounds shift rumen bacterial populations and reduce the incidence of acidosis. Other tools that have developed are direct-fed microbials, including certain bacterial cultures such as Lactobacillus acidophilus and Propionibacterium freudenreichii, which help support rumen pH.

Feeding yeast also shows a potential benefit to support pH levels when receiving high-starch diets. They can also support other health parameters as well. These practices reduce acid load in the rumen by spreading out the fermentation of starch throughout the day. Good bunk management is also important for hand-fed cattle. Empty bunks followed by overfeeding the next day often causes acidosis.

Conclusion

It is doubtful the industry will ever eliminate death loss from digestive upset in feedlot cattle. The use of careful feeding management practices along with effective additives can reduce the incidence of these conditions and help improve performance and profitability.  

PHOTO: High-grain diets pose some risks to feedlot cattle by disturbing normal rumen patterns. Knowing the diseases to follow can protect your livestock. Staff photo.

Dr. Steve Blezinger is a management and nutritional consultant with an office in Sulphur Springs, Texas. Email Steve Blezinger or call at (903) 352-3475. Follow him on Facebook at Reveille Concepts.

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