Nutrient Recommendations -- We believe the nutrient recommendations in Tables 11, 12, 13, 14, 15 and 16 will result in a “bestcost” feeding strategy for most producers the majority of the time. However, certain conditions (i.e., specific genetic populations, economic, nutrient availability, nutrient profile and nutrient interactions) may require significant deviations from the recommendations presented. Also, the current debate surrounding the environmental consequences of nitrogen and phosphorus excretion was considered in the development of amino acid and phosphorus recommendations.
Although crude protein values still appear on feed labels and in some feeding recommendations, we did not list dietary protein recommendations because pigs do not require protein in their diet. Instead they require amino acids, which are found in protein. The recommended levels for the most critical amino acids are given in Tables 11, 12, 13, 14 and 15. Lysine is the first limiting amino acid in grain-soybean meal-based diets. In these diets, there is a strong relationship between the protein and the lysine level of the diet. For example, a corn or milo soybean meal-based diet containing .95% lysine will contain about 18% protein. A diet with .80% lysine will contain about 16% protein and a diet with .65% lysine has about 14% protein.
The recommendations for tryptophan, threonine, methionine and methionine+cystine were derived from an optimum pattern or ratio among amino acids that we established (Table 17). We assumed that the pattern of amino acids required changes throughout the growth stages, except for tryptophan and methionine. Lysine is needed in a much larger proportion for the synthesis of new tissue than for maintenance. Thus, for example, the recommended amount of threonine in the diet as a percent of lysine increases from 64% in the starting phase to 68% in the finishing phase.
The ranges presented for trace mineral and vitamin additions offer feed manufacturers greater flexibility, which often results in cost savings in preparing custom products from our nutrient recommendations. The minimum values generally represent the quantity recommended by the National Research Council (1998). The upper values do not represent the maximum safe or tolerance levels, but instead a reference point above which further additions will not likely improve performance. We do not necessarily recommend supplying minimum or maximum levels on a routine basis. An example of appropriate trace mineral and vitamin additions to pig feed is shown in Table 16.
The recommendations reflect differences in nutrient requirements for pigs according to their stage of production, sex, lean growth rate and milk production. We assumed the same feed intake for pigs with different lean growth rates, an assumption that is not always true. We also assumed pigs are housed under thermoneutral conditions, which is also not always true.
When is it appropriate to alter dietary nutrient density according to feed intake?
• Starting and growing pigs
The daily amino acid and mineral recommendations for starting and growing pigs (8 to 130 lb) were designed for pigs consuming the quantities of feed indicated at the top of Tables 11, 12, 13, and 15. When these pigs consume less feed than indicated, we do not recommend increasing amino acid and mineral concentrations in an attempt to maintain our calculated daily nutrient intakes. In other words, do not attempt to formulate diets for starting and growing pigs for a specific intake of nutrients.
The relationship between lean gain and energy intake is linear for pigs within this weight range. Changes in energy intake directly affect lean gain, which may alter amino acid requirements. If energy is limiting because feed consumption is lower than expected, lean gain also will be lower. In this case, providing more amino acids by increasing the percentages in the diet probably will not improve pig performance. An exception might be when fat is added to the diet and feed intake is reduced because less feed is required to meet the pig's energy requirement. Therefore, increasing the percentages of amino acids and minerals to maintain a constant nutrient:calorie ratio is recommended. However, newly weaned pigs (< 28 days of age) do not respond to changes in energy density of the diet. Nutrient levels should not be adjusted in these diets until pigs have been weaned for about two weeks.
Higher than expected consumption during the starting and growing phases is not a problem and our recommended percentages of amino acids and minerals should be maintained. This will result in daily nutrient intakes that exceed our calculated levels. Energy intake will also be greater than expected, so the additional amino acids and minerals will be needed to support increased lean gain.
• Finishing pigs
At times, it may be advisable to increase the percentages of amino acids and minerals in the diet of finishing pigs (> 130 lb) consuming less feed than indicated in Tables 11, 12, 13 and 15. In other words, it may be appropriate to formulate finishing diets to a specific intake of nutrients. Compared with younger pigs, energy intake and lean gain are not as closely related during this stage. Moderate reductions in energy intake are less likely to affect lean growth rate. Therefore, if actual feed intake is within 90% of listed levels, our calculated daily amino acid and mineral recommendations should be maintained by increasing the density of these nutrients in the diet.
For example, assume 190 to 250 lb finishing pigs were fed a diet containing .55% lysine and their feed intake was 6.4 lb or 2905 g/ day. Therefore, the pigs' daily lysine intake was 16.0 g/day (2905 x .055) which is below that recommended in Table 11. The pigs' lysine intake was reduced because they were consuming about 7% less feed than expected (Table 11). Because the reduction in feed intake is within 10% of the expected amount shown in Table 11, the diet can be reformulated so the pigs consume the recommended amount of lysine (17.2g/day).
Similarly, nutrient density should be increased to maintain a constant nutrient:calorie ratio when fat is added to the diet. However, the percentages of amino acids and minerals in the diet should not be adjusted when severe reductions in feed consumption (> 10%) occur. Examples of when not to increase nutrient density include (1) heat stress resulting from continued exposure to temperatures in excess of 90oF and (2) crowding. During the finishing stages, increases in feed intake may occur during periods when additional energy is needed for maintenance (such as during cold weather). Additional amino acids and minerals are not needed. Thus, we recommend that producers reduce the percentages of amino acids and minerals in the diet to maintain our calculated daily intakes of these nutrients. This recommendation only applies when temperatures remain cold for a prolonged period. Temperatures should be monitored where the pig is (same height and location). Remember that air movement, bedding, humidity and group size affect how pigs perceive temperature.
Including fibrous ingredients in the diet will increase feed consumption. Nutrient density can be reduced in these diets to maintain a constant nutrient:calorie ratio. As temperatures fall below the lower critical temperature, consumption of fibrous diets may not increase to the same extent as for low-fiber diets. This is because (1) feed intake has already increased in response to the reduced energy density and (2) consumption of bulky diets is limited by gastrointestinal capacity. Therefore, reductions in nutrient density other than for energy density are not recommended.
• Adult breeding swine
Breeding boars or gestating sows and gilts fed amounts different from those recommended in Table 14 should receive our calculated daily nutrient intakes. Thus, the percentages of amino acids and minerals should be increased for lower feeding levels and decreased for higher feeding levels. This is particularly important for boars because inadequate amino acid intake can depress libido. If diets designed for higher feeding levels are formulated on a total phosphorus basis, check to see if the daily available phosphorus recommendation in Table 14 is met. It is possible to meet our total phosphorus recommendation but not the available phosphorus recommendation with diets containing large amounts of corn or milo. Lactation diets should not be adjusted when sows consume more feed than listed in Table 14. Adding fat to lactation diets will reduce feed intake slightly. The nutrient:calorie ratio should be held constant in lactation diets containing fat by increasing the percentages of amino acids and minerals.