Volume VIII Number 4 August 2000

Subacute Acidosis:
An Often Unobserved Thief

by Teres Gatz-Lambert

Acute acidosis is usually easy to identify: a dead steer. Subacute acidosis, however, is seldom recognized and yet, according to University of Nebraska's Rick Stock and Robert Britton, probably costs feeders more money than acute acidosis because of the unobserved reduction in cattle performance.

"We have measured nearly a $10 to $13 per head advantage by reducing the effects of acidosis in a wheat diet by adding roughage or replacing with corn," Stock states. (Table 1) "Simply evaluating the effect of feed intake alone, a .25 to 1.0 lb. Reduction in daily feed intake can drastically reduce overall feedlot profit." (Table 2)

He adds that liver abscesses tracing to acidosis may reduce daily gain by as much as 11 percent and may reduce feed efficiency by as much as 9 percent. Plus, lost value due to liver abscesses in a pen of cattle, with a 15 percent incidence rate, may be $3 per head. And that's not counting the loss to the processor for the extra trimming of the carcass that may be required.

Signs

When cattle are fed in groups of 100 to 200 head, the re-searchers admit that identifying individual animals with subacute acidosis may be extremely difficult. Often, they note, it takes an entire pen to be "off-feed" before low feed intakes or erratic intake patterns are observed.

But being off-feed isn't the only sign of subacute acidosis. Other signs include panting, excessive salivation, kicking at the belly, eating dirt and diarrhea.

The researchers stress that nearly every animal in the feedlot will experience subacute acidosis at least once during the feeding period. The reason: Because it's an important natural function in adapting to high-grain finishing ration and any interruption in the normal consumption pattern of cattle can cause acidosis.

"For example, storms can disrupt feed intake by causing cattle to consume greater amount of feed before and after a storm," the researchers point out. "Other environmental effects include mud and heat. Mud and heat reduce feed intake and alter intake patterns. And extreme heat conditions may force cattle to eat a greater proportion of their feed at night, rather than during the day."

Other factors that can impair feed intake include the design of the feedlot as well as the location and operation of waterers.

Misconceptions

Many feeders believe that, if they limit feed offered to a pen of cattle, the up-and-down swings in feed intake can be prevented. This, Britton and Stock states, is a misconception.

"Feed records will show intake variation is small, but this is an artificial situation that does not reflect true feed intakes for two reasons. First, since bunk space is limited in most feedlots, dominant cattle consume all the feed they want. The more timid cattle are limit-fed. Limiting feed only limits feed for the timid cattle, and not all the cattle.

"Second, if feed intake is limited for all cattle, the cattle will be hungry. Rate of feed consumption will be increased at the next feeding, and this change may alter their intake pattern and create additional acidosis, resulting in the roller coaster intake patterns previously described. It is best to not restrict feed intake of finishing cattle in order to prevent acidosis."

When large changes in the amount of feed offered per pen are required, the researchers contend that this usually indicates the feed intakes of the cattle are "moving in unison." In other words all cattle are increasing or decreasing their feed intake. Another reason, they contend, might be previous errors in judgment were probably made concerning the amount of feed offered previously to the pen.

To increase efficiency of digestion in the rumen, the researchers suggest ionophores such as Rumensin and Bovatec.

Although most cattle will recover on their own from subacute acidosis without any medical treatment, the researchers offer 13 management tips:

  • Feed complete-mixed diets. If possible, don't feed grain and hay separately.

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  • Minimize sorting of ration ingredients by the use of a limited amount of silage, molasses or liquid supplement or fat.

  • Feed slowly fermenting grains (dry rolled corn, dry whole corn, dry rolled grain sorghum) with rapidly fermented grains (barley, wheat, steam-flaked corn, high-moisture corn). Limit wheat to a maximum of 40 percent of the diet if not accustomed to feeding wheat.

  • Gradually adapt cattle to high-grain finishing diets in 21 - 28 days using three or four step-up diets. Suggested step-up diets may contain 45, 35, 25 and 15 percent roughage.

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    a) Ration price $5.20/cwt, $.25/day yardage, $.20 interest, $10/head processing b) Based on 5,000 head, 2.4 turns/year
  • Feed at least 5 - 10 percent roughage (dry matter basis). Roughage is similar to insurance. The more roughage fed, the less likely acidosis will be a problem. When acidosis is not a problem, feed efficiency and cost-gain increase as roughage level increases.

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  • Make sure feed intake is not increasing or decreasing before switching cattle to the next ration.

  • Feed bunks should contain a sprinkle of feed (approx. 1 lb./head) or be slicked clean, but still wet with saliva. Never allow the cattle to be without feed for more than 30 minutes.

  • Feed cattle at the same time each day.

  • Feed two or more times a day.

  • Use an ionophore to increase feed efficiency and reduce variation in feed consumption.

  • Balance feedlot rations for .5 - .7 percent calcium.

  • Keep daily records of dry matter feed intake.

  • Keep all waterers clean and fresh.
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