Field peas (Pisum sativum L.) are an annual season grain legume crop and are cultivated in areas that are too cold for the cultivation of soybeans. Market opportunities for field peas have increased in recent years, and the cost of cultivation is less for peas than for soybeans. The concentration of starch in field peas is less, but crude protein and amino acids are greater than in cereal grains. Therefore, in addition to providing amino acids, field peas also provide energy to swine diets, which is important because energy is the most expensive component in diets. As a consequence, it is important to determine the energy value of field peas. Agronomic practices, growing location, and differences among varieties may impact the nutritional properties of field peas, including energy digestibility. It was also observed that in-vitro energy digestibility of field peas was increased by reducing the particle size. However, there is no information on the effects of reducing particle size on concentrations of digestible energy (DE), metabolizable energy (ME), or net energy (NE) in field peas fed to group-housed pigs. Likewise, the digestibility of energy in field peas grown in the U.S. has not been compared with the digestibility of energy of field peas grown in Canada. Therefore, the objective of this research was to test the hypothesis that the particle size of field peas and the location where field peas were grown may affect the apparent total tract digestibility (ATTD) of gross energy (GE) and concentration of NE in field peas fed to growing pigs.  

Experimental design

A single source of field peas from the U.S. was divided into three batches that were ground at 200, 400, and 600 μm. Two different sources of field peas from Canada (i.e., Canada 1, Canada 2) were also used, in which both sources of Canadian field peas were ground at 400 μm. A basal diet containing corn and soybean meal as sole sources of energy without field peas was used. Five additional diets were prepared by including corn and soybean meal and 50% field peas at the expense of corn and soybean meal. Therefore, six diets were used. The ratio between corn and soybean meal inclusion was 1.95:1 in all diets.

Twenty-four growing pigs with an average initial body weight of 30.75 kg (SD = 1.07) were used. Pigs were allotted to one of the six diets using a 6 × 6 Latin square design with six chambers and six periods. Therefore, there were six replicate chambers per diet. Pigs were housed in a group of four pigs per calorimetric chamber. Diets were fed for 13 days, where the initial seven days were considered the adaptation period to the diet.

Consumption of O₂ and CO₂ and CH₄ productions were measured and fecal and urine samples were collected from day eight to day 13. On day 14, pigs were deprived of feed for 36 h, and this time was considered the fasting period to determine fasting heat production (FHP). Total heat production (THP) from pigs fed diets during the collection period and the FHP were calculated (Brouwer, 1965). Concentrations of NE in all diets were calculated by subtracting THP by ME in diets then adding FHP. The ATTD of dry matter (DM) and GE in diets were also calculated. Concentrations of DE, ME, and NE in field peas were calculated by difference (Adeola, 2001).

Results

Results indicated that the ATTD of DM and GE was not different between the basal diet and the 2 diets containing the 2 sources of field peas from Canada and between the basal diet and the 3 diets containing the 3 sources of field peas from the U.S. (Table 1). The ATTD of DM and GE linearly (P < 0.05) increased as particle size of the U.S. peas decreased. The DE, ME, and NE were not different among diets with the exception that the diet containing the U.S. peas ground to 678 µm had reduced (P < 0.05) energy compared with the basal diet and the diets containing the U.S. peas ground to 457 µm and the 2 Canadian sources of field peas. Concentrations of DE, ME, and NE in field peas ground to 678 µm were less (P < 0.05) than in other sources of field peas. Concentrations of DE, ME, and NE linearly (P < 0.05) increased as particle size of the U.S. field peas was reduced from 678 to 265 µm.

Key points

• Concentrations of DE, ME, and NE were not different among different sources of field peas.
• Concentrations of DE, ME, and NE were increased by reducing particle size of field peas.

^a-bWithin a row, means without a common superscript letter are different (P < 0.05).

¹Each least squares mean represents six observations, except for diets containing peas ground to 678 and 265 µm samples (n = 5).

²Linear effects of reducing particle size of field peas from the U.S.