Nutrition for Optimal Performance (adapted from Harper, 1993)

From a producer's viewpoint, the goal of swine feeding is to promote a level of performance that results in the highest rate of financial return over variable costs. In years past, the most important growth traits that influenced rate of financial return were growth rate and feed conversion. Many producers, however, are now faced with the reality that the carcass leanness of their hogs has a major influence on sale price and rate of financial return. Optimum diet formulas and feeding procedures, then, should be considered for maximizing profit.

One measure that combines growth with carcass merit is lean tissue growth rate. High lean gain pigs require more protein and lysine to realize their genetic potential than do medium or low lean gain pigs. High lean gain pigs may be defined as having a rate of lean tissue gain per day of .76 lbs or more from 40 to 250 lb body weight. Medium lean gain pigs have a rate of lean gain of .6 to .75 lbs per day and low lean gain pigs gain less than .6 lbs of lean per day.

Many producers do not know the lean gain potential of their hogs. It can be estimated, however. Many feed companies have programs that can help. Producers can also use information from a packer kill sheet or a group of pigs for which the starting date on feed and average initial weight has been recorded. This information can be applied to a National Pork Producers Council formula to estimate average lean gain per day for the group. The estimation formula for unribbed carcasses using electronically measured fat and muscle depths is provided on page 25 (equation 4B.). The calculation for the starting values uses a formula from Brannamann et al. (1984).

For example, from a packer kill sheet for a load of hogs it is determined that the average carcass weight is 171 lbs, the average backfat is 1 inch (25.4 mm) and the average muscle depth is 1.89 inches (48mm). The producer recorded that this group of hogs was started on feed 93 days earlier at an average starting weight of 45 lbs. The formula is applied to these numbers as follows:

Based on the definition of low, medium and high lean gain pigs, these pigs appear to be performing in the medium lean gain category. If the producer suspects that these hogs are performing below their genetic optimum, the amino acid density of the diet could be increased, and subsequent groups evaluated in a similar fashion. In performance testing, pigs should always be fed to reach their genetic potential. Note, however, that overfeeding amino acids to medium or low lean gain genotypes is of no benefit to carcass merit and is wasteful in terms of feed costs and feed utilization.

Nutrient Recommendations

This section helps establish suitable nutrient levels for desirable performance of breeding stock, based on PIH factsheets, NRC recommendations and current research. Information about diets should be available to prospective buyers, and all diets should be analyzed to ensure that recommended nutrient levels are actually attained in the ration. Test station diets should contain nutrient levels found in Table 5. NOTE: Lysine may be lowered to .80 after the first 35 days. If pigs from high lean lines or boars (see above) are being tested, feed the higher levels throughout the test period. For on-farm tests, the station diets may be used, or the producer may choose to modify the protein levels according to recommendations in Table 6. To standardize formulation of diets fed to swine in central test programs, and for breeders conducting on-farm tests, the diets in Table 7 are given as examples.

^a Adapted from NRC (1988) and PIH factsheets (1995).
^b Should be available in premix form.
* 200 ppm of copper may be added as copper sulfate (CuSO₄) to promote growth. This will require the addition of 364 mg CuSo₄ per lb of diet. This information must be included in the sales catalog.
** Add if salt is not iodized.

Table 7. Example test diets.

	Diet No.1
	1	2	3	4	5	6
Ingredients
Ground corn (8.5% CP)	1258	1374	1353	828	1127	1214
Ground oats (11.5% CP)	--	--	--	500	--	--
Soybean meal (48% CP)	552	436	452	516	617	530
Fat (3585 kcal/lb)	34	33	34	--	100	100
Lysine (78% L-lysine)	--	--	3	--	--	--
Molasses (1060 kcal/lb)	25	25	25	25	25	25
Pellet binder	50	50	50	50	50	50
Dicalcium phosphate (24% Ca:18.5% P)	46	48	48	44	46	48
Ground limestone (38% Ca)	13	12	13	15	13	13
Salt (iodized)	10	10	10	10	10	10
Trace mineral mix, lb2	2	2	2	2	2	2
Vitamin mix, lb2	10	10	10	10	10	10
Total	2000	2000	2000	2000	2000	2000
Calculated Nutrient Levels
Met. energy, kcal/lb	1452	1455	1455	1342	1515	1520
Protein, %	17.60	15.50	15.80	17.90	18.40	16.90
Lysine, %	0.95	0.80	0.94	0.95	1.03	0.92
Calcium, %	0.90	0.90	0.92	0.93	0.93	0.93
Phosphorus, %	0.75	0.75	0.75	0.78	0.75	0.76
Salt, %	0.50	0.50	0.50	0.50	0.50	0.50

¹ Diets balanced on lysine. Amounts are for one ton of feed.
² Amount of trace mineral mix and vitamin mix used may vary, but diet should contain amounts listed in Table 5, in addition to those from diet ingredients. Finely ground corn is recommended as the vitamin carrier.

Diet 1 is the standard test station formula of an 18% corn-soy diet. This diet conforms to the guidelines that the calcium-phosphorus ratio should be at, or near, 1.2:1.

Diet 2 is the 16% corn-soy diet to use if the protein level is reduced at the midpoint of the test (35 days after test initiation), or in on-farm tests where optimum performance is desired, as opposed to maximum lean gain.

Diet 3 is an example diet in which 3 pounds of lysine, 95 pounds of corn and 2 pounds of DiCal are substituted for 100 pounds of soybean meal.

Diet 4 is a conditioning diet to be used after the conclusion of the test to increase bulk and reduce energy. In this conditioning diet 500 pounds of oats is substituted for corn and soybean meal while maintaining the protein level. This diet would be limit-fed to meet the varied energy requirements of different animals after they complete testing.

Diet 5 and 6 are diets to which 5 percent fat is added to increase the energy density of the diets. In these diets, 100 pounds of fat are substituted for corn and extra soybean meal is added to maintain the calorie:lysine ratio. Feed consumption, however, may decrease slightly. If supplemental fat is added to the diet, the level should be stated in the sales catalog. Supplemental fat levels should not exceed 5 percent added fat, and total dietary fat should not exceed 8 percent.

Test station diets should be pelleted. The molasses and/or pellet binder level may vary to accomodate proper pelleting. Meal form diets may be more practical for on-the-farm performance test rations. A feed additive known to be effective and approved by FDA for increasing growth and efficiency is recommended for use throughout the test period. All withdrawal requirements, however, are to be strictly enforced.

Other cereal grains may be substituted for corn, if their use permits achievement of recommended dietary nutrient levels. Because the corn-soy diets are balanced for amino acid content, substitution of other energy sources should be done on an amino-acid basis, as well as on energy content.