Mike Tokach: "The amount of phytase used in pigs has been increasing"

Q: What have been the most interesting findings in your latest research on minerals?

A: I will break it down into a couple of major areas. Recently, we've done a lot of work on calcium and phosphorus, in terms of major minerals, and also with sodium and chloride levels. First on the calcium and phosphorus: in terms of phosphorus requirements, what we are finding is that the pigs in the field, in research barns where we conduct the trials out in commercial production, we have much higher phosphorus requirements than what is listed in NRC as a percentage of the diet. The grams per day requirement is probably not very far off, but because the feed intake is lower, the percentage requirement is somewhere between 115 and 130% of the NRC listed levels, depending on the phase of production. We think that is part of the reason why people are getting such big responses to phytase, when they add high phytase levels to the diet. In some cases, they're not meeting the full phosphorus requirements of the pigs.

Q: Are the formulas being adjusted accordingly now?

A: Certainly, we're seeing that. The phosphorus levels, particularly the amount of phytase that people are using, have been increasing; both because the phytase prices have been pretty reasonable, but also the realization that we're getting benefits to having more digestible phosphorus for these pigs. So, I think that's one major area where we are continuing to do some research. Not only our research but research of others has shown that we're getting these high responses to phytase in the nursery and in the grow-finish period.

The other area that ties very closely to phosphorus is calcium levels, particularly when you use phytase. We've got a number of trials going that are looking at the optimal calcium levels. Calcium really becomes an issue when you are formulating closer to pigs phosphorus requirements. There are some situations, where diets are very close to or below the phosphorus requirements of these fast growing pigs in the field. If you add excess calcium to the diets in these situations, whether you do it on purpose or accidentally (ex. because of too much limestone being put in the diet at the feed mill or calcium coming from other additives that isn't being fully accounted for), all of a sudden you have a diet that's very high in calcium to phosphorus ratio. When that happens, it reduces the utilization of the phosphorus. That makes a borderline phosphorus level become a deficient phosphorus level, or makes a deficient level become even more deficient. Our research shows that this is quite detrimental to performance. On the other hand, if you're at the phosphorus requirement or above, excess calcium doesn't hurt nearly as bad.

Q: How much of the increase in the use of phytase could also be due to benefits in terms of environmental issues?

A: Certainly, the phytase is being used for both, the environmental reasons and cost savings, as compared to the inorganic phosphorus sources in the diet. But where the calcium comes in is that sometimes people don't take into account the full release of calcium that also comes when you use phytase in the diet. So, you can end up with a high calcium level, when you are borderline or deficient in phosphorus. Where phytase comes into play also is when there are mistakes and a good example is if phytase isn't added to the diet at the level that it is supposed to be or the phytase gets heat damaged in a pelleting process or it is not a high quality, reputable phytase source to start with. You can end up with a diet that you thought was adequate in phosphorus that all of a sudden is deficient and that's when that excess calcium level, again, becomes a major issue.

Q: How do you prefer to calculate that calcium level and how much does it vary depending on the phase of production?

A: For calcium, I like to formulate on a ratio relative to phosphorus. You can do this a number of ways: a ratio of the total calcium to total phosphorus; total calcium to digestible phosphorus; or digestible calcium to digestible phosphorus. There is some work to be done with digestible calcium before we are ready to use it for diet formulation. Personally, I like using the analyzed calcium to analyzed phosphorus ratio and trying to keep that ratio between 110 and 125%. Thus, analyzed calcium would be at 110% of the analyzed phosphorus level. Analyzed meaning what the lab analysis would show, not taking into account the phytase release. If you want to account for the phytase release, you want to make sure you are counting it both on the calcium side and the phosphorus side.

When you formulate the diet, I prefer to see that the formulation sheet list a total calculated amount of calcium and phosphorus with the phytase release, the digestible phosphorus, but also what the analytical level of calcium and phosphorus is in the diet. The analyzed values are helpful because that's what you can actually test for and find in the lab. I prefer to use the analyzed calcium to analyzed phosphorus ratio because it's an easy one to remember and to test whether the diets are actually meeting the formulated values or not.

For these ratios, I am talking about nursery and finishing pigs. The only case where I use a different approach would be in sows, particularly in late gestation or in lactating sows, we want to run that ratio just a little bit wider and have a little bit more calcium in the diet, but again you want to make sure that you're not, in any of these phases, deficient in phosphorus.

Q: What can you tell us about the consequences of deficiencies?

A: In the grow-finish pigs, the most common thing we see is just reduction in growth. In our research trials, you can pick up the growth and feed efficiency differences, as they are pretty sensitive if we don't meet the phosphorus requirements. If you do it over a long period of time, you can pick it up in terms of bone breakage, but we don't see that as often in the production systems as just a reduction in growth. Since we moved to CO2 instead of electrical stunning in our slaughtering plants, we don't have the broken vertebrae and blood splatter in the loin that we use to see at the plant when you had low phosphorus diets. Therefore, it's not as easy to pick it up at the packing plant anymore, so you have to be looking at it from a growth standpoint. If you do run into broken bones or broken rib situations in the field, that's usually when we've had a gross deficiency. In these cases, it's usually not a formulation issue but rather a milling or ingredient mistake issue.

Q: What would be the adequate levels of vitamins and which are the most important ones?

A: All of the major vitamins you want to include because they all have different uses in the pig. Certainly, fat soluble vitamins A, D, E and K, are all quite important. We've done a lot of work with vitamin D recently, and with different forms of vitamin D, and we've learned that if you have a diet that's too low on vitamin D you can mess up the calcium and phosphorus metabolism pretty quickly. Vitamin D deficiency causes problems with bone strength, broken ribs, and malformations that can occur. If you have too low of vitamin D levels in utero, it can be a real problem. But at the normal levels that we would add to diets, which are usually two to three times of NRC requirements, we don't see any of these problems.

As far as water soluble vitamins, most pig diets need to have riboflavin, niacin, pantothenic acid and B12 added. For some of these vitamins, you can see noticeable malformations if they are not added at adequate levels. However, in most cases, we just see a reduction in growth or problems at the packing plant with meat quality. Probably, the biggest area that we need to do more work with is the influence of vitamin levels on the long-term shelf life of pork, especially with our export markets. In short-term shelf life studies, it is really difficult to pick up some of the advantages to increasing levels of vitamins in the diet. Thus, long-term studies are needed.

Q: With the current antibiotic reduction, how do you evaluate the use of probiotics and prebiotics?

A: There's definitely a lot more work being done to test different probiotics and prebiotics in pigs. Our National Pork Board has done a tremendous amount of work in funded reviews of literature, trying to understand how to get more value out of research in this area. We have a plethora of products that are available as antibiotic replacements. I think the frustrating part for many of our pork producers is that many of these products do get some benefit, but it's a relatively small benefit as compared to what the antibiotics do in terms of growth promotion. When benefits are found, most of the response to probiotics has been in the nursery stage. For prebiotics, we really have struggled to see positive responses in terms of growth performance with the products that have been tested so far.

We continue to do more work in this area. There's a lot of touted benefits on health, but they are sometimes difficult to pick up unless you do the trials in very large numbers in the field. We need large numbers of pigs to measure changes in numbers of pigs that have to be pulled and put in hospital pens, or in mortality rate.

Probably the area that it keeps coming back to is that we can do some things nutritionally to help the pigs out, but it is a relatively small response as compared to what we can gain with some of the management changes. For example, increasing weaning age has a much greater impact than what we can do with the diet. Changes in the management and in the barn have a bigger impact than most dietary changes.

Q: Is there one probiotic that you would consider the most useful?

A: Different compounds have shown promise, but I would be hesitant to mention one class above the rest because there really isn't one yet at this point that you can say you want to make sure you have in all diets. If you look at commercial diets in the US, there are Lactobacillus products in probably the greatest percentage of nursery diets. Thus, you can probably make an argument that they've done the best job of getting data to convince production systems that they are getting enough benefits to include it in the diet, from an economic standpoint. That would probably be the only major area in terms of a probiotic.

We don’t want to overlook where we started the discussion with minerals. Obviously, in our world, zinc oxide is used in almost every nursery diet for the first two to three weeks after weaning. And copper becomes an important ingredient, particularly after that point. Those minerals give you as much benefit as anything outside of the antibiotics. With zinc oxide, though, people have to be very careful to not keep it on the diet too long, not only because it can start reducing pig performance, but also because of the concerns with high zinc excretion and staph resistance issues that have been associated with pharmacological levels of zinc.