Peas have been used for food and feed for centuries. Research to evaluate their inclusion in swine diets has been conducted largely in Europe, Canada, as well as in the northern Great Plains and Pacific Northwest regions of the United States. Genetic advances in swine growth, feed efficiency, carcass yield and fat to lean ratios, and meat quality are putting increasingly greater demands on dietary requirements. Field peas are in demand to meet these requirements because they are low in fiber, serve as a good source of high quality protein, possess highly digestible energy, and are a good mineral source, as shown in Table 1.

Anti-nutritional factors (ANF) are common to seed from all pulse crops. Protease inhibitors are proteins with specific anti-trypsin and anti-chymotrypsin activity that decrease protein digestibility and cause pancreatic hypertrophy. However, spring seeded (Pisum sativum) peas resulting from white-flowered cultivars (hortense) that yield yellow and green seed are uniquely low in ANFs. European researchers reported trypsin inhibiting activity of raw peas to be from five to 20 times less than that reported for raw soybeans. Anti-nutritional factor levels are distinctly higher among winter pea (Pisum sativum) dark flowered cultivars ( arvense) with respect to swine feeding and therefore are best suited for feeding to ruminants. While pigs can tolerate low ANF levels with good success, pig age and digestive tract development must be considered when formulating diets for very young early-weaned pigs. The good news, with the exception of early weaned pigs, is that practical pig diets formulated with field peas can be prepared and direct-fed without prior treatment to inactivate ANFs.

Protein in a diet consisting of a mixture of ingredients is referred to as crude protein and is defined as the nitrogen content X 6.25. This is based on the assumption that, on average, the nitrogen content is 16 g of nitrogen/100 g of protein. Since the building blocks of proteins are amino acids, modern swine diets are formulated around an ideal protein concept that corresponds to the needs of the animal for 10 essential amino acids. Lysine has been determined to be the first limiting amino acid for swine, so four ideal amino acid ratios to lysine have been developed for maintenance, protein accretion, milk synthesis, and body tissue. Table 2 lists the amino acid composition of soybean meal and field peas, the true ileal digestibility of each amino acid, and each field pea amino acid digestibility expressed as a percentage of soybean meal. That field peas are an excellent source for high quality protein is illustrated by the high true ileal digestibility values shown for each amino acid. Levels for the sulfur containing amino acids methionine and cystine are lower than desired. Necessary replenishment is accomplished through supplementation with either synthetic crystalline methionine or by including small amounts of a complementing protein source like canola meal.

 

Table 1.Nutrient comparison of selected protein sources.
	Peas	Soybean Meal	Canola Meal
Crude Protein, %	22	44	38
ME Energy, kcal/lb	1430	1465	1225
Fiber: ADF, %	7.2	12.7	5.4
NDF,	8.9	17.2	21.2
Lysine, %	1.68	2.9	2.27
Methionine+Cystine, %	.52	1.24	1.05
Calcium, %	.11	.32	.63
Phosphorus, %	.41	.62	1.17

Table 2.Amino acid content and true ileal amino acid digestibilities of field peas expressed as a percent of soybean meal. (NRC, 1998).
	SBM A. Acid Cont.	Pea A. Acid	SBM Digest.	Pea Digest.	% of SBM
Lysine	2.83	1.50	89	88	99
Arginine	3.23	1.87	93	90	97
Histidine	1.17	.54	90	89	99
Isoleucine	1.99	.86	88	85	97
Leucine	3.42	1.51	88	86	98
Methionine	.61	.21	91	84	92
Cystine	.70	.31	84	79	94
Phenylalanine	2.18	.98	88	87	99
Threonine	1.73	.78	85	83	98
Tryptophan	.61	.19	87	81	93
Valine	2.06	.98	86	83	97

Starter (Weanling) Pig Diets

In modern swine production, pigs are commonly weaned from 14 to 21 days of age, weighing from 11 to 16 pounds, and are fed highly nutrient-dense diets. During the first two to three weeks of life, a pigs digestive enzymes are only capable of digesting lactose (milk sugar), glucose, casein (milk proteins), and certain fats. Enzyme physiology changes occur between two and seven weeks of age such that the pig becomes increasingly more capable of efficiently digesting starch, sugars, non-milk proteins, and fats. By three weeks of age, enzyme turnover has progressed sufficiently such that a milk-based diet can be replaced with dry feedstuffs consisting of some milk co-products (whey, dried skim milk, etc. ), cereal grains, and high quality proteins.

Research in Europe, Canada, and North Dakota with starter diets have evaluated both raw and extruded pea replacements for soybean meal and corn ranging from 20 to 50%. Extruding is a process whereby feeds are forced through a small orifice in the end of a heavy steel barrel by an auger-like device. Clearance between the heavy steel auger flighting and flighting on the wall of the barrel is narrow. When feed, and an appropriate amount of water or steam is forced through the device at high RPM friction heat is created in the range of 250-290 ^oF. European investigators have shown that extrusion decreases ANF and significantly increases ileal starch digestibility. When varying levels of raw or extruded peas (15, 30, and 45%) were fed to pigs from 15.4 to 55 pounds, adding raw peas tended to depress growth rate and efficiency at all levels fed. However, following extrusion, growth and efficiency among pigs fed either 30 or 45 percent peas was comparable to performance of pigs fed a wheat/soy control diet.

The swine industry has adopted earlier weaning as a common practice in which pigs are weaned between 14 and 16 days of age. Successful weaning programs with pigs of this age rely on precise nutrient balance and phase feeding adjustments that allow the nutritionist to reduce nutrient density as pigs mature. Field pea research at the Dickinson Research Extension Center has focused on the use of peas in nutrient dense, 4-phase, early-weaned pig diets. In the first of three investigations, starter diets for 14.5 day old pigs weighing 10.8 pounds were prepared with raw or extruded peas that replaced either 30 or 50% of the diet. Overall pig performance was not improved compared to the corn/soy control diet. Within pea treatments, extrusion heat treatment did improve pig performance at the 30% replacement level. In a second investigation (Table 3), pigs weaned weighing 16 pounds were studied in which raw and extruded peas replaced 20 and 40% of the diet. Overall, the 40% replacement level depressed growth and efficiency.

Within pea replacement, extrusion improved pig performance at both the 20 and 40% levels. Replacing 20% of the diet with either raw or extruded peas resulted in nearly comparable performance to that of the corn/soy control diet.

A third evaluation (Table 4) was conducted to determine timing for introduction of extruded peas in an early weaning program. Fourteen day old pigs weighing 11.8 pounds were fed a nutrient dense 4-phase starter program over 35 days. Pigs received either a corn/soy control diet, a 20 percent extruded pea diet initiated at weaning, or a combination diet in which pigs received the corn/soy control diet for the first two weeks post weaning followed by the 20% extruded pea diet for the remaining three weeks of the 35 day starter period. At the time the pigs were switched from the control diet to the extruded pea regime, they were 28 days of age and weighed 25 pounds. Thirty-five day pig growth and efficiency favored the time delayed combination method.

In practical, nutrient dense, phase-fed, pig starter programs it is suggested that pea replacement in the total diet not exceed 20% for extruded peas and 15% for raw peas. Data has shown that peas can be fed to very young pig immediately after weaning; however, best performance and efficiency will be obtained using a 20/20 rule in which peas are withheld from pigs until they have attained 20 days of age and 20 pounds body weight.

 

Table 4.Timing of pea application for pigs weaned at 14 days of age (Landblom and Poland, 1997).
	Corn/Soy	20% Extruded Pea at Weaning	Corn/Soy Wks 1 & 2; Extruded Pea 20% Wks 3-5
Start Wt., lb.	11.3	11.2	11.2
35 Day Wt., lb.	35.0	32.5	36.6
Gain, lb.	23.7	21.3	25.4
ADG, lb.	.68	.61	.73
ADFI, lb.	1.14	1.09	1.20
Feed:Gain, lb.	1.68	1.79	1.65

Growing-Finishing Pig Diets

Worldwide, the majority of all peas are fed to growing-finishing pigs for several reasons: 1) It is a time during the pig's growth profile when digestive enzyme turnover is complete. 2) Growing pigs over 10 weeks of age are more tolerant to low levels of ANF. 3) Feed intake is greatest during the finishing period. 4) Peas have frequently been used to lower growing-finishing diet cost/unit of gain. As stated, peas are deficient in sulfur-containing amino acids, which are not generally considered to be a dietary problem in protein dense starter diets, but must be replenished in growing-finishing diets if other protein sources are being completely replaced with peas. Pig performance reported in Canadian research with 44 - 132 lb. pigs was depressed when peas replaced soybean meal; however, once methionine shortages were replenished performance was equivalent to control diets. Numerous studies with pea replacement for soybean meal in growing-finishing diets have shown, when amino acid balance is correct, peas can replace all of the protein and a portion of the basal feed grain.

Two options for replenishing sulfur containing amino acids include the addition of synthetic crystalline methionine and feeding a complementing pea/canola meal blend. Canadian research has shown that pea/canola meal blends can replace all of the soybean meal and sulfur containing amino acids in growing-finishing diets. The two protein sources complement each other because peas are a rich source of the amino acid lysine and are also high in digestible energy. Canola meal, on the other hand, is high in methionine and cystine but lower in digestible energy. Growing-finishing research conducted by Landblom et al. (2001) evaluated a pea/canola meal blend that was further enhanced with the enzyme additives phytase and xylanase (Table 5). A pelleted corn/soy control diet was compared to ground meal-type pea/canola meal diets prepared with either of the enzymes alone and in combination. Pelleting improved growth and efficiency for pigs receiving the control diet. All pigs performed very well using pea/canola diets and adding phytase and xylanase enzymes enhance d growth and feed efficiency further.

The energy content of canola meal is approximately 14.3 percent lower than peas. Therefore, a balanced amino acid profile using a peas and canola meal, that doesn't compromise total dietary energy is essential to obtain optimum growth performance. Table 6 shows an example of typical levels for peas and canola meal in barley and corn diets that do not compromise dietary energy.

Review of a number of studies show pea inclusion levels range from 35 to 40% of the diet during the grower phase and from 10 to 43% during the finishing phase. Variations in the level of peas added in diet formulations is based on the targeted growth phase and protein supplementation needs of the basal grain. For example, wheat and hull-less oat growing-finishing diets require less supplemental protein from pea than lower protein grains such as corn. Four-phase growing-finishing diet formulations, such as those shown in Table 7, illustrate how the nutritionist adjusts pea levels to match basal feed grains. The table also summarizes growth performance and carcass measurements resulting from the diets shown.

Carcass Quality of Pigs Finished With Peas

Research data relating to carcass quality is not nearly as extensive as that for growth and efficiency. However, data available indicates that feeding peas has no effect on backfat thickness but may increase intra-cellular fat (marbling). Carcass measurements shown in Table 7 are typical of lean growth resulting from diets formulated with peas.

Feeding Peas With Wheat Screenings

Peas are a versatile feedstuff that can be fed in dietary formulations with a variety of feed grains and by-products. A study at the Dickinson Research Extension Center looked into pig response when wheat screenings replaced 20, 40, and 60% of the corn. The level of peas was held to 20% of the diet. When corn was replaced with either 40 or 60% screenings growth performance and efficiency were depressed. However, as the price of competing ingredients increased the pea supplemented diets with either 40 or 60% screenings became cost effective choices. Thus, peas can be used in cost conserving approaches that utilize by-products like screenings.

   

Table 6. Pea and canola meal inclusion levels in barley and corn grain-bases.
	Stage 1 (50-80 lb)	Stage 2 (81-140)	Stage 3 (141-190)	Stage 4 (191-250)
Barley	64%	66%	71%	73%
Peas	22%	23%	22%	20%
Canola Meal	12%	9%	5%	5%
Corn	50%	53%	57%	59%
Peas	36%	34%	31%	30%
Canola Meal	12%	11%	10%	9%

  

Table 7.Pea inclusion levels in four-phase diets prepared with barley, corn, and naked oats. (Landblom and Poland, 1998).
Phase 1 (50-80 lb)	Diet 1	Diet 2	Diet 3	Phase 2 (81-140 lb)	Diet 1	Diet 2	Diet 3
Peas	35	35	35	Peas	10	25	40
SBM	—	—	8	SBM	—	—	4
Corn	—	—	54.3	Corn	—	—	53.8
Barley	—	62.2	—	Barley	—	72.5	—
Naked Oats	62.4	—	—	Naked Oats	—	87.4	—
Phase 3 (141-190 lb)				Phase 4 (191-250 lb)
Peas	10	15	43	Peas	10	10	40
Corn	—	—	55.1	Corn	—	—	58.0
Barley	—	82.8	—	Barley	87.8	—	—
Naked Oats	87.8	—	—	Naked Oats	—	87.9	—
Growing-finishing performance resulting from the four-phase diets.
		Barley/Pea		Corn/Pea		Naked Oat/Pea
Start Wt., lb.		56		56		57
Final Wt., lb.		253		256		261
Gain, lb.		197		200		204
ADG, lb.		1.81		1.95		2.02
ADFI, lb.		6.35		6.03		5.59
Feed:Gain, lb.		3.51		3.0		2.77
Carcass measurements resulting from the four-phase diets.
		Barley/Pea		Corn/Pea		Naked Oat/Pea
Hot Carcass Wt., lb.		184		183		185
Percent Yield, lb.		74.8		74.4		75.3
Percent Lean, lb.		53.7		54.2		52.9
Fat Depth, in.		.72		.74		.80
Loin Depth, in.		2.07		2.23		2.04
Fat Free Lean Index		49.1		48.9		48.2

Effect of Feeding Peas to Lactating Swine

Available data suggests peas can replace a portion of the soybean meal in sow lactation diets. Research at the Dickinson REC evaluated replacement of up to 30% of the soybean meal in lactation diets. Daily feed intake and metabolizable energy consumption were similar across treatments, suggesting pea replacements for up to 30% of the soybean meal did not compromise dietary energy consumption. Sow performance was unaffected by the level of pea grain in the lactation diet, and as such, lactation sow weight change from farrowing to weaning and days to first estrous did not differ. Sow milk composition sampled mid-lactation on day 14 for total milk solids, protein, and fat was similar to that of control sows. Sow body condition based on ultrasound backfat depth measurement was also not effected by pea replacement. Sows receiving a 10% replacement for soybean meal weaned more and heavier pigs than the other treatments and tended toward greater pig survival than the control and other levels of pea replacement. These data suggest that pork producers can replace up to 30% of the soybean meal in lactation diets with peas without compromising sow performance, milk composition, return to estrous, litter performance, and litter survival rate. Concerns raised relative to potential antigenic responses to the proteins (legumin and vicilin) in litters from sows fed pea diets are unwarranted and should not be of concern.

Effect of Feeding Peas to Breeding Swine

Specific data relative to feeding peas to breeding boars, sows, and gilts is limited. Although documented studies are not available, the large body of existing data for all other classes of swine would not cause concern among nutritionists desiring to formulate with peas. Developing formulations for breeding swine using peas would be appropriate and justified when peas are competitively priced compared to other feedstuffs.

Conclusion

Information available pertaining to feeding peas to swine encompasses all phases of production. In the past, peas have been an economical source of high quality protein and energy. However, if producers of peas are to continue growing the crop they must be adequately compensated for their production efforts. Therefore, peas of the future will likely demand a higher value in the marketplace. While there are limitations to the level of peas that can be fed to the various production classes of pigs, virtually all classes are capable of consuming some quantity of peas in their diet. For best results, starter pigs should not consume diets containing more than 15% raw peas or 20% extruded peas. It is further suggested that early weaned pigs be at least 20 days of age and weigh a minimum of 20 pounds before receiving starter diets with peas included. For growing-finishing pigs, substantial evidence exists demonstrating that peas can replace all of the soybean meal and a portion of the basal grain in wheat, barley, and hull-less oat grain bases, and that 4 to 8% soybean meal or other protein source will need to be added to pea/corn grower pig diets due to the low protein content of corn. Strong supporting evidence clearly supports the use of peas and canola meal as complementing protein, energy, and mineral sources. Lactating sows also benefit from partial replacement of 30% of the soybean meal in sow lactation diets. All things considered, peas are an excellent feedstuff for swine.

Literature Cited

Landblom, D.G., R.L. Harrold, W.W. Poland and K.A. Dawson. 2002. Effects of Fibrozyme and phytase enzymes on growing-finishing pig performance in field pea-canola meal supplemented diets. J. Anim. Sci. Vol. 80 (Suppl. 1).

Landblom, D.G. and W.W. Poland. 1998. Supplementing grain energy sources with field peas and full-fat canola seed in swine growing-finishing diets. In the Dickinson Research Extension Center Annual Report www.ag.ndsu.nodak.edu/dickinso/research/tocreports.htm.

Landblom, D.G. and W.W. Poland. 1997. Nutritional value of raw and extruded field pea in starter diets of segregated early weaned pigs. In the Dickinson Research Extension Center Annual Report www.ag.ndsu.nodak.edu/dickinso/research/tocreports.htm.

NRC. 1998. Nutrient Requirements of Swine (10^th Ed.). National Academy Press, Washington, DC.

EB-76, May 2002

• Introduction to Field Pea Blaine Schatz
• Field Pea in Beef Cattle Diets Vern Anderson
• Field Peas in Dairy Cattle Diets J.W. Schroeder
• Field Pea in Sheep Diets G.P. Lardy, M.L. Bauer, E.R. Loe
• Field Pea in Poultry Diets R.L. Harrold