Market opportunities for field peas (Pisum sativum L.) have rapidly increased for livestock feed and human food, due of the high nutritional quality of pea protein. However, as is the case with some feed ingredients, differences in soil, varieties, agronomic practices and growing method may change the nutritional characteristics of the peas as well as digestibility of nutrients. In addition, it is possible that differences in the particle size of field peas change the digestibility of energy and nutrients as has been reported for other ingredients. However, information about the effects of particle size of peas on digestibility of starch and amino acids (AA) are limited. Additionally, there is limited research to compare the digestibility of AA among field peas produced in different regions of the U.S. and Canada. Therefore, the objective of this experiment was to test the hypothesis that the apparent ileal digestibility (AID) of crude protein and starch, and the standardized ileal digestibility (SID) of AA in field peas may be affected by the particle size of the field peas and the region where the field peas were grown.

Experimental design

A single source of field peas from U.S. was divided in two batches that were ground at 200 or 400 μm. Two different sources of field peas from Canada (i.e., Canada 1, Canada 2) were used, in which Canada 1 field peas source was divided in two batches and were ground at 200 or 400 μm, whereas Canada 2 field peas source was only ground at 200 μm. Five diets were formulated including one of each source of field peas as the only source of AA and starch. An N-free diet was also formulated to calculate basal endogenous losses of AA and CP. Thus, a total of 6 diets were used. All diets contained 0.40% chromic oxide as an indigestible marker.

Six growing pigs with an average initial body weight of 50.5 ± 3.7 kg were used. Pigs were equipped with a T-cannula in the distal ileum and allotted to one of the 6 diets using an 6 x 6 Latin square design with 6 diets and 6 periods. Each experimental period lasted 7 days. The initial 5 days of each period was considered an adaptation period to the diets and ileal digesta were collected for 8 hours on day 6 and 7 using standard procedures. The diets and ileal digesta were analyzed for crude protein, AA, starch, and chromium to calculate the AID of crude protein, AA and starch, and SID of AA in each diet containing field peas. Statistical analysis were performed to test differences among ingredient sources.  

Results

The AID of crude protein was greater (P < 0.05) in the Canada 1 source ground at 400 µm compared with the other sources, but there was no difference on AID of crude protein among field peas sources ground to 200 µm (Table 1). There were no differences in AID of AA among of field peas sources. However, the AID of starch was less (P < 0.01) in U.S. field peas source ground at 400 µm compared with other field peas sources.  

The SID of crude protein was greater (P < 0.05) in Canada 1 field peas source ground at 400 µm than in U.S. field peas source ground at 200 µm (Table 2), but did not differ from the other field peas sources. However, the SID of most AA was not different among of field peas sources.

Key points

• In this experiment, the AID and SID of AA was not affected by the particle size and region where field peas were produced.
• The AID of starch in field peas produced in U.S. increased if ground at 200 μm, but this was not observed for field peas produced in Canada.
• The SID of crude protein in field peas was affected by the region were produced, but it was not affected by the particle size.

Table 1. Apparent ileal digestibility (AID) of crude protein, starch and AA (%) in three different sources of field peas ground at 2 different particle size¹.

^a-cWithin a row, means without a common superscript differ (P < 0.05).

¹Each least squares mean is the mean of 5 observations per treatment.

Table 2. Standardized ileal digestibility (SID) of crude protein, and AA (%) in three different sources of field peas ground at 2 different particle size^1,2.

^a-cWithin a row, means without a common superscript differ (P < 0.05).

¹Each least squares mean is the mean of 5 observations per treatment.

²Values for SID were calculated by correcting the values for apparent ileal digestibility for basal ileal endogenous losses. Basal ileal endogenous losses were determined (g/kg of dry matter intake) as CP, 14.98; Arg, 0.66; His, 0.18; Ile, 0.32; Leu, 0.48; Lys, 0.38; Met, 0.07; Phe, 0.31; Thr, 0.46; Trp, 0.09; Val, 0.40; Ala, 0.60; Asp, 0.74; Cys, 0.18; Glu, 0.93; Gly, 1.68; Ser, 0.46; and Tyr, 0.22.