Research has yet to find a sole additive that can accomplish all of the following: increase production, improve reproductive performance, improve milk composition, and improve profitability without causing any health problems. However, there are feed additives available that are beneficial for specific problems.

   While some additives only have a high-pressure sales person backing its claims, many additives are backed by substantial research and have proven valuable. Unfortunately, it may occasionally be difficult to determine validity of research behind an additive. Table 1 gives guidelines for determining the benefits of feed additive use on dairy operations. Following is a discussion of some feed additives that have proven effective under specific circumstances.

Buffers
Buffers help maintain a constant pH. When high-grain rations, rations high in rapidly fermentable carbohydrates, or rations with small particle size are fed to ruminants, the rumen environment becomes more acidic, dropping from a normal pH of 6.5 to a pH as low as 3.0. Saliva contains a natural buffer, sodium bicarbonate. When chewing is not stimulated, saliva production is reduced which allows pH in the rumen to decline further. Rations which contain silage as the only forage and high-moisture corn can also be too acidic for the ruminant.

   In an acidic rumen, the normal cellulolytic bacteria cannot survive, causing lower nutrient digestibilities, lower feed intakes, and lower milk production. Although the underlying cause of the acidosis should be determined and controlled by feeding a well-balanced ration, adding buffers to diets that have the potential of lowering ruminal pH is beneficial.

   The most commonly used buffers are sodium bicarbonate (bicarb), magnesium oxide, sodium bentonite, sodium sesquicarbonate, and magnesium limestone. Potassium carbonate is also an effective buffer and can supply additional potassium needed during the summer in warmer climates. A combination of these compounds usually provides a more effective buffer supplement than one individual buffer alone.

Yeast Cultures
Yeast cultures have proven effective in increasing rumen bacteria numbers and stimulating cellulolytic bacteria growth. Cellulolytic bacteria convert fiber to energy utilized by the cow and other rumen microbes. Because of yeast cultures' effect on rumen microbes, fiber digestibility can increase and amino acid production can be improved, which has a positive impact on protein and fat content of milk.
 
   Yeast cultures also buffer the rumen by increasing the activity of fiber digesting bacteria. Claims for Saccharmyces cerevisiae, a yeast, indicate lactic acid utilizing bacteria are also stimulated, which reduces the amount of lactic acid in the rumen. In effect, lactic acid utilizing bacteria buffer the rumen to help reduce the symptoms of acidosis.

   Yeast cultures are generally very palatable, and many producers use a yeast culture source in dairy cow rations. Yeast cultures are commonly used in rations for cows experiencing heat stress or in early lactation rations. Feed intake and digestibility are extremely important in these two situations. Yeast cultures can increase the amounts of cellulolytic bacteria which, in turn, can improve feed utilization.

Mineral Complexes and Chelates
Some trace minerals are bound or complexed with an organic substance such as an amino acid, protein, or carbohydrate. Most chelated or complexed minerals are bound to specific amino acids or proteinates (combination of amino acids). Chelating or complexing these trace minerals will increase absorption of the mineral in the small intestine. Increased absorption of these trace minerals may improve immune response. Additionally, some mineral chelates have been shown to interact when they're absorbed, stimulating the immune response.

   Chelates have been shown to have a positive influence on SCC, hoof health, reproductive performance, and milk production in cows experiencing stress. Trace minerals that are most commonly complexed or chelated are zinc, manganese, copper, and cobalt. New research on trace mineral complexing with organic substances will probably lead to the availability of more trace minerals in this form. When all other causes of high SCC, poor hoof health, or poor reproductive performance have been exhausted, mineral chelates or complexes may play an important role in alleviating these problems.

Direct-Fed Microbials (DFM)
Although many producers and nutritionists believe that DFMs are beneficial to stressed cows, controlled research trials showing a positive affect are lacking. However, some field trials have shown a benefit in feeding DFMs to cows just fresh. The DFMs seem to help fresh cows make a smoother transition from a high-forage diet to a diet high in grain.

   The strength of microbial supplements is usually measured in colony forming units (CFU) of live viable microbes. Microbial products contain Lactobacillus (lactic acid producers) and some also contain other beneficial bacteria. Some testimonials and field research indicate that many producers don't observe the normal drop in feed intake around parturition when DFMs are fed. The significance of maintaining feed intake immediately following calving is metabolic problems will be reduced and higher peak yields can be achieved.

   The precise mode of action of DFMs is not know. Stress, such as calving, enables the number of E. coli bacteria in the rumen to grow and disrupt the balance of lactic acid producers. Disruption of digestion then occurs and, consequently, performance will be hindered. Lactobacillus, found in DFMs, restore the microbial balance, stabilize rumen pH, decrease ammonia production, and may enhance production of beneficial enzymes which aid in digestion.

Mycotoxin Binders
Several compounds, such as aluminosilicates or mannan oligosaccharids, may help alleviate the negative affects associated with certain mycotoxins in feed. It appears a mycotoxin's ability to be absorbed by the animal may be hindered when a mycotoxin binder-type compound is included in the ration.

Niacin
Niacin, a B vitamin, is involved in energy metabolism. Fed two or three weeks before and after freshening, niacin is well known to help reduce the incidence of ketosis. When a dry cow nears calving and a mobilization of large amounts of fatty acids is expected (normally because the cow is overconditioned), the use of niacin reduces the rate of fat mobilization. To help reduce the incidence of ketosis, niacin should be fed before and after parturition. As with any other additive, individual response will vary.

   Some research studies have shown niacin can alleviate the protein suppressing effect that feeding supplemental fat has on milk protein. However, research on this subject is somewhat conflicting and this effect should be closely monitored on individual farms.

Anionic Salts
Anionic salts are designed to be fed to dry cows within two to three weeks of calving. These salts supply anions to counteract a high cation dry cow ration. Cations include calcium, potassium, and sodium. When high calcium and/or potassium forages must be fed to dry cows, anionic salts fed to close-up dry cows can help eliminate clinical and subclinical cases of milk fever and other metabolic disorders in fresh cows. Urine should be tested with a strip of pH paper or a pH meter to make sure the anionic salts are inducing metabolic acidosis in the close-up dry period.

   Anionic salts are not palatable and must be mixed thoroughly in a palatable TMR. They should only be fed to close-up dry cows in situations where it is not possible to feed low calcium and low potassium forages. Anionic salts have been shown to cause calves to be weak for a few days after birth. This could be important if calves of that age are not aggressive in suckling.

Protected Amino Acids
The exact amino acid requirements for the lactating cow are not known. Rumen microbes supply the majority of amino acids that reach the intestine, especially in lower-producing cows. However, in some cases, undegradable or bypass protein is needed to meet the amino acid requirements of high-producing cows. For these high producing cows, most experts will agree that methionine is the first limiting amino acid and may be co-limiting with lysine. Therefore, many different types of synthetic amino acids designed to bypass the degrading action of the rumen microbes are now on the market.

   Many research studies have shown the benefits of supplementing synthetic amino acids to diets of cows. Milk protein and milk production are both improved. However, feeding synthetic amino acids in place of rumen undegradable protein that has an amino acid profile which is high in essential amino acids (fish meal and blood meal) must be economical. To determine if protected amino acids can pay for themselves, calculate ration costs with and without protected amino acids and determine the improvement (if any) derived from the protected amino acids.

Cobalt Glucoheptanate
The addition of cobalt to rations in the form of cobalt glucoheptanate has been shown to significantly improve fiber digestion by rumen bacteria. Cellu-lolytic bacteria in the rumen digest fiber and cobalt is a very important nutrient for these bacteria. Cobalt glucoheptanate is most beneficial in situations where forage quality is poor or when forage digestibility is especially important.

Determining Additive Effectiveness
All rations should be correctly balanced initially without the use of additives. If, after feeding a well-balanced ration, cows aren't performing as well as expected in a specific area, one additive can be added to the ration according to label instructions. Calculate income over feed cost without the additive. After feeding the additive for one month, calculate income over feed cost again. Calculate the effect on the "bottom line." If at least a break even exists along with some other improvement that is important, such as an improvement in body condition, the additive may have been beneficial. For some additives two weeks may be adequate time to determine the effectiveness, but for most additives one month is the suggested minimum time to determine its effect.