Field peas (Pisum sativum L.) have been cultivated for centuries for human consumption, due to the high nutritional quality of pea protein. However, during the last years, increasing demand for field peas for livestock feeding has developed a market in Canada, Europe, and the U.S. Therefore, 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 the digestibility of nutrients. Besides that, differences in the particle size of field peas may change the digestibility of nutrients. Therefore, the objective of this experiment was to test the hypothesis that the standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AA) in field peas is 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 the U.S. was divided into three batches that were ground at 600, 400, and 200 μm. Two different sources of field peas from Canada (i.e., Canada 1, Canada 2) were used, in which both sources of Canadian field peas were ground at 400 μm. A basal diet without field peas contained corn and soybean meal as sole sources of amino acids. Additional 6 diets were formulated based on corn and soybean meal and 50% field peas. The ratio between corn and soybean meal inclusion was constant in all diets at 1.95:1.00. An N-free diet was also used to determine basal endogenous losses of AA and CP. Thus, a total of 7 diets were used. All diets contained 0.40% titanium dioxide as an indigestible index.

Seven growing pigs with an average initial body weight of 60.6 ± 2 kg were used. Pigs were equipped with a T-cannula in the distal ileum and allotted to one of the 7 diets using a 7 × 7 Latin square design with 7 diets and 7 periods. Each experimental period lasted 7 days. The initial 5 days of each period were considered an adaptation period to the diets and ileal digesta were collected for 8 hours on days 6 and 7 using standard procedures. The diets and ileal digesta were analyzed for CP, AA, and titanium to calculate the apparent ileal digestibility values in each diet containing field peas. The SID was calculated by correcting the apparent ileal digestibility with the basal endogenous losses. The SID of CP and AA in each source of field peas was calculated by difference. Statistical model included source as fixed variable and animal and period as random variables. If the model was significant, means were separated. Contrast coefficients were also used to test linear and quadratic effects of reducing particle size of field peas from the U.S.

Results

Concentrations of CP in 5 sources of field peas ranged from 19.07 to 20.42% (Table 1). Coefficient of variation (CV, %) for CP and all AA in the 5 sources of field peas less than 5%, which means that variations of CP and AA among the sources used in this experiment were low. The SID of CP and all AA was not affected by different sources of field peas (Table 2). Values for the SID of CP and all indispensable and dispensable AA except for Arg in the 3 sources of field peas from the U.S. were not affected by reducing particle size. However, the SID of Arg was linearly (P = 0.042) increased by reducing particle size of field peas from the U.S.

Key points

• Analyzed CP and AA did not vary among the 5 sources of field peas used in this experiment.
• The SID of CP and AA was not affected by different origins or different particle size.
• The SID of Arg was linearly increased by reducing particle size of the U.S. source.

Table 1. Analyzed CP and AA in field peas, as-is basis

Table 2. SID of CP and AA in field peas¹ (n = 7)

¹Values 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, 10.54; Arg, 0.39; His, 0.13; Ile, 0.28; Leu, 0.40; Lys, 0.29; Met, 0.07; Phe, 0.26; Thr, 0.44; Trp, 0.08; Val, 0.31; Ala, 0.43; Asp, 0.58; Cys, 0.16; Glu, 0.76; Gly, 0.97; Pro, 2.68; Ser, 0.37; and Tyr, 0.20.