Summary
High variation in crude protein and starch contents is observed among peas collected in farms of Western Canada. The paper aims to evaluate the impact of that variation on the energy value of peas in pigs.

Introduction
Feed producers are concerned by the high variation of composition observed among the pea samples collected throughout the Prairies. However, it is unclear whether this variation affects the energy value of the peas.

Results and discussion
A total of 50 pea samples were collected in Saskatchewan, Alberta and Manitoba in 2005. Their analysis confirms the high rate of variation in composition, especially in crude protein and in starch contents (Table 1). This is in agreement with the observations of the Canadian Grain Commission (20 to 26% for crude protein, Nang & Daun, 2004). However, a detailed analysis of the results shows that the majority of the samples had a protein content ranging from 23 to 24% of the dry matter (Figure 1).

In 1998, Zijlstra et al. determined the digestible energy (DE) of 11 pea samples collected in Western Canada and obtained DE values ranging from 3100 to 3740 kcal/kg. This represents a 20% variation, which is lower than the variation observed for crude protein and starch, for example. Unlike what is observed in cereals, no relationship could be established between the neutral detergent fibre (NDF) content and the energy value.
Different hypotheses can be emitted. First, the NDF content of peas does not reflect their actual dietary fibre content. Peas contain, on average, 10-12 % NDF whereas the real dietary fibre content ranges from 19 to 25% of the dry matter (Table 1). The difference is due to the fact that the NDF method with detergents is not appropriate for pulse grains and to the presence of soluble fibre, namely pectin and oligosaccharides. No information is available on the effect of these undetected components. Second, more than 90% of the pea fibres are fermented in the digestive tract of the pig and we do not know how this affects the digestive processes. Finally, fibre fermentation provides energy to the pig, in the form of volatile fatty acids, but to an extent that still needs to be determined.
Researchers at Prairie Swine Centre are currently working on the estimation of the net energy value of pea samples differing in composition. They aim to use Noblet’s equations of prediction. The latter are based on the composition and digestibility of the diet. Some equations are only based on composition (see example):

NE = 2790 + 4.12 x EE + 0.81 x Starch – 6.65 x Ash – 4.72 x ADF

where EE (ether extract) is the fat content and ADF the acid detergent fibre (ligno-cellulose) content (Noblet et al, 1994).

This equation was used here to estimate the NE value of the 50 pea samples and the results range from 2,460 to 2,680 kcal NE/kg. The range of variation (8%) is thus much lower than the variation observed for protein or starch contents.
According to that equation, ash is the main is factor that affects NE, whereas starch plays a limited role and protein has no effect at all. Peas are quite low in ash but the content is very variable. Wang and Daun (2004) observed higher variation than in the present study (1.3 to 3.4%) and ascribe the variation to potassium, which represents 40% of the total mineral content. The fat content is also an important component of energy but, as for ash, the levels in peas are very limited. The last component is ADF or ligno-cellulose but the latter is the most stable components of peas (from 6.5 to 8.6%; Wang & Daun, 2004).

Conclusion
In summary, it is likely that the variation in energy value of peas will be lower that what the variation in protein and starch contents might suggest because the latter don’t affect energy digestion very much and that the components that could affect energy supply are either present in low amounts in peas (ash, fat) or don’t vary very much (ADF).

Acknowledgements
Strategic funding provided by Sask Pork, Alberta Pork, Manitoba Pork Council and Saskatchewan Agriculture and Food Development Fund. Research is funded by Saskatchewan Pulse Growers and Alberta Pulse Growers.