Rumen: Feed Additives for Beef Cattle

One of the best methods to reduce feed costs is through the use of feed additives. Their primary effects are to improve feed efficiency and/or daily gain. Some feed additives have secondary benefits which include reducing the incidence of acidosis, coccidiosis, and grain bloat, while others suppress estrus, reduce liver abscesses, or control foot rot problems.

Feed additives can be divided into five general categories: 1) ionophores; 2) antibiotics; 3) estrus suppressants; 4) buffers; and 5) others. Each feed additive has its own characteristics and feeding limitations. Some are approved to be fed in combination with others. Using the proper level of feed additives is very important because too high a level will decrease animal performance, especially with cattle on low-quality roughages.

Ionophores

Ionophores are a type of antibiotic that depresses or inhibits the growth of specific rumen microorganisms. This selective inhibition alters rumen fermentation in three major ways:

1. Ionophores improve the efficiency of energy metabolism by changing the types of volatile fatty acids produced in the rumen and decreasing energy lost during fermentation of the feed. Improved animal performance results from increased energy retention during fermentation in the rumen.

2. Ionophores decrease the breakdown of feed protein and may also decrease microbial protein synthesis. This has minimal effects on the performance of cattle on high-grain diets, but may have important implications with growing cattle fed high-roughage diets.

3. Ionophores may reduce the incidence of acidosis, grain bloat, and coccidiosis. Reducing these stresses should result in improved animal performance.

Ionophores include monensin, lasalocid, salinomycin, and narasin. At present, monensin (RumensinTM) and lasalocid (BovatecTM) are the only ionophores approved to be fed to beef cattle.

With high-grain diets, ionophores generally decrease feed intake, improve feed conversion, maintain or increase daily gain (Tables I and II), and do not affect carcass characteristics. When cattle in confinement (feedlot) are fed diets containing large proportions of roughage, ionophores improve daily gain and feed conversion. Feed intakes of animals fed high-roughage diets do not change if the proper level of ionophore is fed.

Summary of ionophore trials with feedlot cattle (1979, 1980, 1981).

	Percent improvement over negative control
No. of Trials	Gain	Intake	F/G
Rumensin	53	+ 2.5	- 5.1	+ 7.2
Bovatec	17	+ 6.4	- 4.6	+ 9.9

Wagner, 1982 Oklahoma Cattle Feeders Seminar.

When starting cattle on feed, step-up programs have been shown to be useful. Feeding 10 grams per ton of Rumensin during the step- up period and then switching to 25 to 30 grams per ton of Rumensin when cattle are on feed improves daily gain, feed intake, and feed efficiency compared to starting cattle on 30 grams per ton of Rumensin. Because Bovatec does not reduce intake as much as Rumensin early in the feeding period, the response to a step-up program would probably be less. Cattle started on feed without ionophores will have more erratic feed intake patterns, and possibly more digestive problems.

Ionophores also decrease the breakdown of feed protein and thus increase the bypass of the protein to the small intestine. This effect is maximized in growing rations when natural protein (no urea) is supplemented below the animal's requirement.

The level of ionophore is also important when cattle are consuming low-quality forage diets. Feeding too high a level decreases the number of cellulolytic bacteria present in the rumen, which can cause reduced fiber digestion. Also, when protein is slightly below the animal's requirement, the ionophore may reduce the breakdown of feed protein and a shortage of rumen nitrogen, needed by the rumen microbes for growth, results. This shortage of nitrogen results in reduced fiber digestion. Thus, the proper level of ionophore depends on the quality of the forage being fed.

The effects of ionophores and growth promoting implants are additive and should be routinely used together.

Rumensin

Rumensin is marketed by Elanco Products Company, a Division of Eli Lilly and Company, for improved feed efficiency for beef cattle fed in confinement (feedlot) for slaughter, improved daily gain in cattle on pasture, and improved daily gain in replacement heifers. It is not cleared for use in cows, and is very toxic to horses and swine. Rumensin can be included in both dry and liquid supplements, and can be fed with either tylosin (TylanTM) or melengestrol acetate (MGATM).

Bovatec

Bovatec is marketed by Hoffman-LaRoche, Inc. for improved rate of gain and feed efficiency for beef cattle fed in confinement (feedlot) for slaughter and improved rate of gain for cattle on pasture. It is not cleared for use in cows. Bovatec is less toxic than Rumensin, but is still not safe for horses and swine. It can be included in both dry and liquid supplements. Antibiotics and MGA are not cleared to be fed in conjunction with Bovatec.

	Finishing Cattle	Growing Cattle
Rumensin
Expected Growth Response:	1 to 3 percent improvement in daily gain; 6 to 8 percent improvement in feed efficiency.	5 to 15 percent improvement in daily gain; 8 to 12 percent improvement in feed efficiency

Level of Use:	20 to 25 grams per ton of air dry ration or 200 to 250 milligrams per head per day.	Pasture--100 to 150 milligrams per head per day or 300 to 400 milligrams every other day. Corn silage rations--150 to 200 milligrams per head per day.

Required Withdrawal Time:	No withdrawal required.	No withdrawal required.

	Bovatec
Expected Growth Response:	4 to 6 percent improvement in daily gain; 6 to 8 percent improvement in feed efficiency.	5 to 15 percent improvement in daily gain; 8 to 12 percent improvement in feed efficiency.

Level of Use:	30 grams per ton of air dry ration or 300 milligrams per head per day.	Low quality forage--100 to 150 milligrams per head per day; Medium quality forage--150 to 200 milligrams per head per day; Corn silage rations--200 milligrams per head per day.

Required Withdrawal Time:	No withdrawal required.	No withdrawal required.

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Rumen: Feed Additives for Beef Cattle

Maximising efficiency in finishing beef cattle

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