Peas in petfood
The lowly pea appears to be an effective ingredient for the next generation of dog and cat diets
As petfood companies and pet owners continue to explore a broader range of ingredient options, the lowly pea (Pisum sativum) has been gaining in popularity. Not to be confused with the fresh or succulent green pea, the type that is being used in an ever widening array of applications is dried peas. These peas are part of a group of seed legumes known as pulses-leguminous dry seeds removed from their pods (a general description of these pulses was provided in a previous column.
Dried peas, commonly known as split peas or field peas, along with several co-products such as pea fiber and pea protein concentrate, are being used on a routine basis in petfood-in some cases taking a very prominent position on petfood ingredient panels. Given their growing popularity, a look at their acceptability, processing effects, regulatory status, nutritional benefits or challenges is probably in order.
Peas are an annual cool season legume grown in temperate climates around the globe. In North America they are more commonly produced in the central and high plains of northern tier states and further north into central and western Canada. Because peas are legumes and fix nitrogen in the soil, they are considered a tool in sustainable agriculture strategies and fit well in rotations with more traditional grains. Peas are planted in the spring once ground temperatures warm past 40ËšF and are harvested in late summer to early autumn.
The dried seeds store well and for the most part are handled much like their cousin, the soybean. They are commonly sold in green and yellow varieties and offered as whole peas, split peas or pea flour. The milling of peas does not require exceptional effort, and once ground, they mix well with other dry ingredients. In petfood, peas extrude in a "controllable" and "predictable" fashion (Pulse Growers of Canada, 2009). From a labeling perspective, peas are considered to be an acceptable ingredient by most regulatory bodies around the world.
Most dried peas end up as split peas in soups, milled (i.e., flour) for a variety of food preparations or used as livestock feed. For petfood, they represent a gluten-free ingredient option outside the grain category. Plus, with a protein content of approximately 25%, peas are conveniently midway between the grains and rendered protein meals so they can play a substantial role in helping meet targeted protein levels.
The protein in peas is a good source for most of the essential amino acids, especially lysine. The sulfur amino acids (i.e., methionine and cysteine) are considered first limiting, with tryptophan close behind. This makes peas a good amino acid complement to most grains and meats.
Peas are relatively low in fat but have a good fatty acid profile, with nearly half derived from the essential polyunsaturated linoleic (C18:2n6) acid, and they contain a small complement of the omega-3 linolenic (C18:3n3) acid. The ash (i.e., minerals) level in peas is lower than that found in animal protein meals (relative to the protein content), making them a good option in low ash cat formulas. Among the minerals, peas are a rich source of potassium.
There are a few dog and cat studies in which peas constitute a significant portion of the diet. For starters, in extruded dry diets with peas included at levels up to 15%, they were reported to be well accepted in palatability tests (Phelps et al., 2004; Behnke, 2005). In two recent papers in which dogs and cats were fed pea-rich diets (66%), it was reported that digestion of starch and protein was slightly less than diets based on corn and rice (Carciofi et al., 2008; de-Oliveira et al., 2008).
This may not be a negative, though. The cause may be due to the pea's relatively high concentration of insoluble fiber (approximately 24%) and more "slowly digestible" or "resistant" starch (Bednar et al., 2001). Plus, peas contain indigestible oligosaccharides such as raffinose, stachyose and verbascose in amounts ranging around 3.5 to 4.5%. These are the compounds found in beans that are known to produce intestinal gas.
Despite the effects on digestibility, it is these carbohydrate differences that may help explain why the dogs and cats fed the pea diets in these studies had quicker glucose clearance rates and lower circulating insulin levels than those fed corn and (or) rice diets. The implications of this are substantial for diets intended to help control blood sugar and diabetes. The downside is that the combination of functional fiber and oligosaccharides might be an issue with elimination and gassiness.
Slightly larger stool volumes and higher stool moisture were reported by these researchers, but the large amount of peas in the diet didn't have a negative impact on stool scores. Further, no information was found in the popular press, research literature or veterinary case studies that reported gassiness associated with pea-based diets.
Peas have some other minor drawbacks besides some of the potential carbohydrate challenges. Like most plant ingredients, peas contain several anti-nutrients. Examples include phytates and oxalates, enzyme-binding proteins like trypsin inhibitor and lectins, polyphenolics and isoflavones and indigestible oligosaccharides.
The phytates and oxalates are known to affect mineral availability and utilization. While these need to be accounted for during mineral fortification, the level in peas is only a fraction of what you might find in other ingredients such as wheat bran or spinach. If fed raw, the trypsin inhibitor and blood-agglutinating lectins can be a health issue, but with moderate heat treatment-similar to that used in most petfood processes-these anti-nutrients are rendered benign.
The polyphenolic compounds (e.g., ferulic and para-coumaric acid) and isoflavones (e.g., daidzein and genistein) have activities ranging from antioxidants to hormones. While found in measurable quantities in peas, the levels are insignificant when compared to the total phenolics encountered in grains like sorghum or the isoflavones found in soy.
No different than any other ingredient, peas may have some minor issues that have to be considered when incorporating them into the diet. Common inclusion levels for petfoods are around 15%, with solid evidence to suggest that exceeding 50% does not cause any harm. So, on the balance, peas appear to be an effective ingredient to consider for the next generation of dog and cat diets.