The pig does not have a specific requirements for crude protein, but rather for the individual components or sub-units that make up protein, called amino acids. Proteins are made up of several different combinations of approximately 20 different amino acids. During the process of digestion, proteins are broken down into individual amino acids that are absorbed into the bloodstream. The amino acids are then incorporated into new protein molecules. When formulating diets with commonly available grains and protein sources, the level of crude protein typically used to describe the diet usually will contain adequate amounts of amino acids to meet the pig's requirement. However, it is important to remember that this is not always true when using synthetic amino acids and alternative or by-product feed ingredients, and that the dietary levels of amino acids should always be checked. It is becoming increasingly important to specify lysine levels when formulating and evaluating swine diets.
If a diet is inadequate in any essential amino acid, protein synthesis cannot proceed beyond the rate at which that amino acid is available. This is called a limiting amino acid. Another way of describing a limiting amino acid is thinking of protein as a rain barrel and the amino acids as the individual staves making up the barrel. If one stave (amino acid) is shorter than the others (limiting), the barrel can only be filled to the level of the shortest stave. In the pig, a deficiency of one or more amino acids will result in depressed growth rate, poor feed conversion, unthriftiness, or reduced reproductive performance. Therefore, protein quality can be defined as how closely the essential amino acids in the protein source come to meeting the pig's estimated requirement for those amino acids.
The 10 essential amino acids that must be provided in swine diets are: lysine, threonine, tryptophan, methionine (and cystine), isoleucine, histidine, valine, arginine, and phenylalanine (and tyrosine). Most cereal grains are limiting in lysine, tryptophan, and threonine. Therefore, when evaluating feed ingredients, these amino acids, especially lysine, are most important in determining protein quality.
When substituting other protein sources for soybean meal, it is important to consider the maximum level at which the new feed ingredient can replace soybean meal without seriously affecting performance. Table 5 is a list of alternative protein sources that can be used in starter, growing-finishing, gestation, and lactation diets to replace all or part of the soybean meal. By using this table, you can determine the maximum replacement rate of the feed ingredient for soybean meal. For example, corn gluten meal can replace 25 percent of the soybean meal protein in the diet.
Protein sources are classified into two major categories: animal (tankage, meat and bone meal, fish meal, or dried skim milk) and plant (soybean meal, cotton seed meal, or corn gluten meal). Soybean meal is usually the most economical source of high quality protein available to North Carolina swine producers. It is the only plant protein that compares with animal protein that compares with animal protein in terms of quality of amino acid content and ratio and ban be sued as the only protein source in most swine diets. Therefore, there is no need to have both animal and plant protein sources in a swine diet, with the exception of starter diets, which should contain dried whey and (or) dried skim milk.
Producers in North Carolina and other states may have the choice of buying either 44 percent or 48.5 percent crude protein soybean meal. The primary difference is that 44 percent soybean meal is made by adding soy hulls to 48.5 percent soybean meal. In addition to the lower fiber content, transportation costs may favor buying the 48.5 percent soybean meal.
In order to determine the relative feeding value of alternative protein sources, it is important to compare the lysine level in the new protein source to soybean meal. The relative feeding values of some alternative protein sources are listed in Table 6. This can be used to determine the comparative economic value of the protein source as a partial or complete replacement to 44 percent soybean meal. These feeding values were calculated by dividing the lysine content of the feed ingredient by that of 44 percent soybean meal (2.90 percent lysine) and multiplying by 100 to put them on a percentage basis.
Assuming that 44 percent soybean meal can be purchased at $250 per ton, what would a ton of 48.5 percent soybean meal be worth? Because the lysine content of 48.5 percent soybean meal is 3.12 percent and 44 percent soybean meal has 2.90 percent lysine, 48.5 percent soybean meal has 108 percent the feeding value of 44 percent soybean meal (3.12/2.90 X 100 = 108 percent). Therefore, if 108 percent is multiplied by the cost of 44 percent soybean meal (108 percent X $250), 48.5 percent soybean meal is of greater value than 44 percent soybean meal if it costs less than $270 per ton.
This section lists some of the more common substitutes for soybean meal in swine diets. Very often, these feed ingredients may appear to be economical compared to soybean meal. However, there are often many hidden costs or disadvantages in using these feed ingredients that are not reflected by their price. These include storage costs, anti-nutritional factors, product variability, fiber content, spoilage, and under-or over-processing. These factors are especially problematic in by-product protein sources. Because by-product feed ingredients tend to vary more in composition, proper information regarding chemical composition is necessary to ensure optimum pig performance.
Some varieties of rapeseed contain high levels of a toxic compound, glucosinolate, which effects thyroid functioning. However, new cultivars of low-glucosinolate rapeseed (µ1 mg/g) have been developed and are commonly referred to as canola meal to distinguish it from the older varieties of high-glucosinolate rapeseed. It is not advisable to feed meals from the cultivars of rapeseed. Reduced palatability, high fiber, and low digestible energy have been causes of slightly poorer performance of pigs fed diets containing canola meal. Canola meal can be used to replace up to 50 percent of the protein from soybean meal in growing-finishing and sow diets without adversely affecting performance.
Home processing by roasting or extruding of raw soybeans, if done properly, results in excellent sources of protein. On-farm roasting or extruding yield "full-fat" soybeans, which, in some instances, are among the cheapest means of adding fat to swine diets. Because of the economic relationship between soy oil and soybean meal and the cost of other fat sources and incorporating them into your feed mill, it may be more economical to utilize full-fat soybeans instead of selling the beans and buying back soybean meal.
Because whole or full-fay soybeans have less protein and lysine than soybean meal (32 to 37 percent protein and 2.1 to 2.4 percent lysine), it is necessary to add 20 to 25 percent more whole soybeans than soybean meal to have similar protein level in the diet. At the same time, this will supply approximately 3 percent added fat to the diet, which will improve feed efficiency approximately 3 to 5 percent. Whole soybeans have an approximate feeding value of 90 to 95 percent that of soybean meal. The following equation can be used to determine if feeding full-fat soybeans is economically justified:
A = cost advantage per ton of full-fat product
Y = cost of one ton of 44 percent soybean meal
Z = cost of one ton of feed grade fat
S = cost of one ton of soybeans
C = cost of processing one ton of soybeans
If it is feasible to feed full-fat soybeans, A will be greater than zero.
High-lysine corn can refer to at least two varieties of corn that contain higher lysine levels than normal corn. The first commecial high-lysine corn was Opaque-2 corn. However, a new variety of corn was developed in Latin America and may be found in the U.S., it is referred to as quality protein maize (QPM). The differences between opaque-2 and QPM are significant, especially with regard to appearance and handling. Opaque-2 corn is a variety of corn that has been selected for improved protein and is higher than regular corn in all essential amino acids except leucine. Because the lysine content is higher in opaque-2 and QPM corn than that of normal corn (.40 and .38 vs. .24 percent, respectively), diets using opaque-2 or QPM corn should be formulated on a lysine basis. The major disadvantages of opaque-2 corn are reduced yields and decreased kernel durability, which are not reportedly problems with the QPM variety.
Excessive heat will reduce the availability of the amino acids, particularly lysine, in feed ingredients. If your soybean meal or dried whey looks darker than usual or has a burnt smell, it is possible that the protein quality has been reduced.
Synthetic amino acids, if added properly, can reduce feed costs and maintain pig performance. Lysine and methionine are the two feed-grade amino acids most commonly added to swine diets. However in the future, synthetic threonine and tryptophan may be available at prices low enough to add to swine diets. Research has demonstrated that supplemental lysine can reduce the amount of soybean meal needed in swine diets. Therefore, adding synthetic lysine can reduce the crude protein level of the diet without affecting performance.
The most common source of synthetic lysine is L-lysine monohydrochloride, which is 78 percent lysine. In diets for pigs over 50 pounds body weight, 100 pounds soybean meal can be replaced by the addition of 3 pounds L-lysine HCl and 97 pounds grain per ton. If the 3 pounds L-lysine HCl and 97 pounds grain are cheaper than 100 pounds soybean meal, the diet costs would be reduced by using supplemental lysine. In sow diets, 50 pounds of soybean meal can be replaced by 48.5 pounds of grain and 1.5 pounds of L-lysine HCl.
Protein sources vary greatly in quality and quantity. Protein quality is directly dependent on the content of the most limiting amino acid relative to the pig's requirement. If a diet is not balanced correctly, a shortage of one of the essential amino acids will reduce growth rate and performance. An amino acid imbalance may occur if a second limiting amino acid is added to a diet when the first limiting amino acid is still deficient. This will result in a reduction in feed intake and reduced pig performance.
On the other hand, when a diet is balanced for the most limiting amino acid (usually lysine), other amino acids are usually in excess of the pig's requirement. Some commercial companies are using the concept of amino acid balance or ideal protein in their sales promotions. This refers to formulating a diet in which all amino acid levels are very similar to the pig's requirement without excesses. However, there is not scientific information to indicate that the excesses of amino acids that occur naturally in milo- or corn-soybean meal based diets will have a detrimental effect on pig performance.
Suggested amino acid recommendations are usually based on the amount of an amino acid required to maximize rate of gain. However, slightly higher levels of amino acids will further improve feed efficiency and carcass leanness. This is because the higher amino acid levels allow the animal to deposit greater amounts of lean tissue rather than fat. Because it takes less energy to deposit lean than fat, feed efficiency is improved. Slightly higher levels of amino acids may be economical to producers who market their hogs on a lean value system, where there is incentive for producing lean pork. In this situation, increasing the lysine content of finishing diets by .05 to .1 percent is suggested.
On an amount-per-day basis, barrows and gilts require similar amounts of amino acids. However, because gilts typically consume 1/2 pound less feed per day than barrows, they may not eat enough to fully meet their requirements. Although sometimes difficult to accomplish on the farm, split-sex feeding offers some feeding and marketing alternatives. Split-sex feeding involves sorting gilts from barrows and feeding each separate diets. Because gilts consume less feed than barrows, their diets can be fortified with extra amino acids for growth rate and feed efficiency as well as calcium and phosphorus for bone development, if they are going to be retained for the breeding herd.
Marketing programs taking advantage of the better feed efficiency of gilts can also be used with split-sex feeding. In general, feed gilts a diet containing .10 percent more lysine than the diet for barrows. Suggested lysine levels for producers who split-sex feed are listed in Table 7.
Pigs are like people, and when the weather gets hot, their appetite decreases. During the summer months, it is advisable to provide drip cooling or cool-zones to keep pigs cool. Increasing the energy and amino acid levels of the diet will also help to offset decreased feed intake. With increased amino acid and energy levels in the diet, the pig will still be consuming the required amounts of each nutrient regardless of the reduced intake, helping to prevent summertime stall-out. A typical recommendation is to increase the lysine level of the diet .10 percent during the warm months of the year (see Table 7).
Although two protein sources may contain the same amounts of a certain amino acid, because of some difference in the chemical structure of the protein, processing method, or anti-nutritional factor, not all of that amino acid may be available to the pig. This is especially true for certain by-product feed ingredients or feed ingredients that have been over-processed.
More and more information about amino acid availability is being published for a variety of by-product feed ingredients, such as cotton seed meal, meat and bone meal, and blood meal. If you are using a high percentage of these feed ingredients, you may want to consider balancing the diet on an available amino acid basis. However, if you are using milo or corn and soybean meal, there is probably no need to worry about amino acid availability.
A pig will adjust its feed intake to meet its energy requirement. When the energy density of the diet increases, a pig will tend to eat less feed. Thus, in diets with added fat, it is important to increase the concentration of amino acids. This way, the pig will consume approximately the same amount per day even though feed intake is less.
Although there is little information on what is the optimum calorie:protein ratio for pigs, it may be possible to extrapolate ratios from standard grain-soybean meal diets to those with high levels of added fat (> 5 percent). A typical grain-soybean meal-milk product diet will have approximately 3.7 g lysine/Meal metabolizable energy, whereas a grower and finishing diet will contain approximately 2.5 and 2.0 g lysine/Meal metabolizable energy, respectively.
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