February, 2000 . Volume 23, Number 1 
NCSU Extension Swine Husbandry
February, 2000 . Volume 23, Number 1
How can you decide whether it's profitable to change your farm's system and adopt a new procedure? The obvious answer is to run your own on-farm trial, but having a reliable control group and staff who carefully follow experimental protocols are significant problems. On the plus-side we now have large pig-farming systems that enable us to generalize the results to more farms and pigs than in the past. Consequently, the up-front fixed costs of running the trial can be s\pread over more animals, resulting in an increased return-on-investment (ROI).
If you are planning a trial, ensure you are prepared to allocate sufficient resources (time, money, people, and pigs) to the project. Consider your specific objectives and how the trial will provide the information you will need to decide whether to adopt the product/procedure. It is essential to decide what you are going to do with the information derived before you run the trial. If you do not have access to the capital required to pay for the new product/procedure, regardless of how efficient it may be, there is no point in running the trial wait until you do.
Decide beforehand exactly what you will evaluate and the improvements you are looking for. For example, if you are considering a change in vaccination protocol, then you should probably evaluate more than one vaccine, different times of vaccination, and different routes of vaccination. If the product is a feed additive, then you should probably evaluate the effect of increasing inclusion amounts. How will you evaluate the effects of the products? For a feed additive, you would measure at least growth rate and feed efficiency. For a vaccine, you might record a change in prevalence of clinical signs as well as some indicators of growth efficiency. Deciding what you will do with the results will help ensure that you collect the information you need. For example, say you are considering whether to implement a new management procedure that you hope will increase the number of pigs born alive but you know will take extra time to implement. Don't spend all your effort measuring the improved performance and forget to record the time it takes to implement the procedure.
Here's a note on the experimental structure of the trial now that the fundamental decisions have been made: Will you collect information on individual pigs, pens of pigs, barns of pigs, or pig farms? Usually researchers collect performance data on individual sows but gather pen data on grow-finish pigs. Increasingly, the industry is comparing farms, but remember that you need a lot of barns or farms to detect real differences in the production parameters of interest.
Now you must determine how you will assign treatments to the experimental units (pigs, pens, barns, or farms). The simplest, and very common approach, is to assign at random. Randomization implies that all units have an equal chance of receiving any treatment, and it prevents systematic bias that occurs when treatment and control animals do not start off equal. For example, if the treatment is given to all the small pigs and the control is the big pigs, then the trial has a systematic bias. The two commonest designs that prevent systematic bias are complete randomization and randomized complete block. The Latin square and split-plot designs are available but are rarely used because they are more complicated. In the complete randomization design, treatments are assigned completely at random. In the randomized complete block design, the experimental units are grouped (blocked) on the basis of some readily measurable variable such as breed or sex. Within these blocks, treatments are allocated at random. Blocking minimizes variation and helps ensure that any observed differences in response are due to treatment. Not surprisingly, it pays to have a statistician involved.
With a big enough sample size you can prove statistical differences exist even though they may be so small as to be practically insignificant. However, this is rarely the situation I encounter in the field. Usually, there are insufficient experimental units put on trial and, as you would expect, when we come to analyze the results the differences may be statistically insignificant, but the differences measured are large enough for us to wish that they were. The solution is to put sufficient units on trial without wasting resources. For example, if you want to detect a difference of 0.5 pigs per litter then you need 250 sows for each product/procedure you are testing and 250 controls. The number of units you need is best determined with the aid of a statistician familiar with pigs and the natural variation in the variables of interest such as pigs per litter.
Finally, be sure when you design the trial that you measure any covariates of interest on the experimental units. For example, if you are allocating treatments to sows and you have decided to block on parity then it may improve the precision of your measurement of litter size if you also record the covariates' age and breed.
Once the data are in and the results analyzed you will know if there are statistically significant differences between the treatments. The significance is usually stated in terms of a "P" value. For example, if P is equal to, or less than, 0.05 (P< 0.05), then that your trial demonstrated with at least 95 percent confidence that the differences recorded are real. Scientists are very cautious about recommending a change unless P< 0.05. However, that doesn't mean that you should be! Accepting P< 0.05 implies that you never change anything unless you are 95 percent confident that you can repeat the positive results of your trial. I submit that most managers would not need that level of confidence in the results—particularly if there are large profits to be made. For example, if my farm trial demonstrated a 0.5 pig improvement in litter size (P=0.15) but it only cost $1/sow to implement, then I would adopt the new treatment and watch the results. For that profit, I'm comfortable being just 85 percent confident that I'll get a 0.5 pig improvement.
Checklist to use when running a farm trial:
Never
• Change the treatments half-way through the trial.
• Use another barn as the control unless barn is the experimental
unit (then you'll need lots of barns).
• Treat the big pigs and use the smaller pigs as controls. Randomize.
Randomize. Randomize.
• Allow people to move pigs across treatments.
• Assume everyone involved knows what is going on. Remember,
Africanized ('Killer') bees left an experimental station in Brazil because the weekend
relief worker didn't know to leave the screens in place!
Always
• Check with a statistician.
• Decide what you are going to do with the results before you start.
• Decide if the unit of investigation is to be a pig, a pen of pigs,
a barn of pigs, or a pig farm.
• Decide how you will collect the data you need.
• Decide how you will analyze the data beforehand you start.
• Allocated sufficient resources (people, animals) to the trial.
• Provide the appropriate "data collection forms" for
staff to use.
• Have a written protocol and discuss it with everyone involved.
• Decide how will you communicate the results to the participants
and the decision-makers.
After the trial is over and the decision about implementing the change, has been made, take the time to plan how any change will be incorporated into standard operating procedures. The best-laid plans surely fail unless they can be implemented.
Morgan Morrow
Currently, land application of animal manure is based on nitrogen. Applying manure based solely on nitrogen requirements has been shown to increase the phosphorus content of the land. As phosphorus accumulation may lead to environmental problems (in the long term), rules for land application of waste based on phosphorus are possible. Land application based on phosphorus would double the size of the land area needed under current production conditions.
In cases were the ability to land-apply waste is limited, alternative methods to either deal with the manure or to prevent the production of the waste will be needed. From a nutritional standpoint, several methods exist to reduce phosphorus excretion.
Analyzing a large number of feed samples obtained in North Carolina, Dr. Jerry Spears noticed that the phosphorus content was typically 50 percent higher than what was actually needed by the animal. This can partially be explained by the practice of feedmills adding extra phosphorus just as a safety measure. In light of Spears, findings, such safety measures are not only costly but can be harmful for the industry. Feed-mills should (are encouraged to) formulate feeds to the actual animal requirement, not above. They also should put quality controls are put in place to actually mix the feeds to match the formulation.
Evaluating the requirement of phosphorus yields some interesting contradictions. Phosphorus, which has several roles in the animal, yields different responses depending on the parameter evaluated. For example, the requirement for phosphorus to maximize bone strength is typically 0.1 percent point higher than the requirement for maximal growth. Although there may be ethical concerns with feeding to maximize growth rather than bone strength as it potentially affects animal welfare through broken bones, etc., from an environmental stand it is possible to reduce P excretion by 30 percent simply by feeding to maximize growth rather than bone strength.
When trying to match the phosphorus level in the diet as closely as possible to the requirement of the animal, it is critical to formulate diets are based on the available or digestible phosphorus content of the feedstuffs, not the total content. Availability of phosphorus in different feedstuffs sources ranges from not available at all for, e.g., cotton-seed meal, to highly available for mono-calcium phosphate. This variation in availability also offers opportunities to reduce phosphorus excretion. Sources with a low availability lead to a high excretion of phosphorus, and thus selection of only highly available sources of phosphorus is important (see Table).
New directions in plant breeding will actually provide varieties of corn and soybean meal that have a much higher phosphorus availability as compared to conventional corn and soybean. In conventional corn and soybean meal, most of the phosphorus is present as phytate. Phytate is a complex of a sugar and phosphorus that pigs cannot digest, thus leading to the wasting of phosphorus. Plant breeders have succeeded in replacing this phytate phosphorus in new varieties of corn and soybeans with other forms of phosphorus that have a much higher availability (see Table).
Biotechnology is providing another solution to the phytate problem in the form of phytase. Phytase is a naturally occurring enzyme that can break down the phytate complex, thus making the phosphorus available. Diets properly formulated using phytase typically reduce phosphorus excretion by 30 percent. As a fringe benefit, phytase also improved the digestibility of other nutrients such as copper, zinc, calcium, and amino acids. The increase in amino acid digestion is likely to be on the order of 1 to 2 percent.
In summary, potential problems with phosphorus-based land application can be reduced substantially through precision nutrition, the use of highly digestible phosphorus sources, and phytase. Technically, reductions in phosphorus excretion on the order of 50 percent are achievable; practically, such a decrease may increase production costs. But by working smart, large decreases are still feasible with a minimal impact on economics.
| Corn | ||
| Low-phytate corn | ||
| Soybean meal 48 | ||
| Soybean meal 44 | ||
| Wheat | ||
| Wheat bran | ||
| Meat & bone meal | ||
| Poultry byproducts | ||
| Fish meal | ||
| Dicalcium phosphate |
Theo van Kempen
The PRV Advisory Meeting was held on December 9, 1999. The committee approved the proposed change in the Administrative Code to require PRV-quarantined swine coming into North Carolina to be shipped under seal with a VS Form 1-27 permit. Also, vehicles used in hauling such swine should be cleaned and disinfected before hauling other livestock.
Summary of the National PRV status:
• 33 states are in Stage V.
• 8 states are in Stage IV.
• New Jersey is in Stage III/IV.
• All other states are in Stage III.
• Approximately 312 herds remain under quarantine for PRV in the
United States.
Morgan Morrow
A memorial fund has been established in memory of Charles Stanislaw, which will help students from the areas of the world where he worked. Contributions can be made to the Department of Animal Science, payable to the Charles Stanislaw Memorial Fund, Box 7621, NC State University, Raleigh, NC 27695-7621.
Todd See