Field peas have been produced mainly for human consumption, but lastly, the industry has been included in diets fed to livestock due to its content of starch and protein. In diets for swine, only peas that are harvested at maturity are used. Almost 80% of P in non-oilseed legumes is bound to phytate, and pigs do not synthesize an adequate amount of endogenous phytate to liberate the P bound to phytate. Therefore, the digestibility of P in field peas is relatively low. Values for apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of P in field peas have been reported, but there are no comparative values for the ATTD and STTD of P among different varieties of field peas at different particle sizes. Therefore, the objective of this experiment was to test the hypothesis that there are no differences in the ATTD and the STTD of P among different sources of field peas fed to young pigs and the second hypothesis was that there is a linear increase in the ATTD and STTD of P as the particle size of field peas increases.

**Experimental design**

Three sources of field peas were used. There were 2 different sources of field peas from Canada (particle size = 200 µm) and there was 1 source from the U.S. (particle size = 600 µm). The field peas from the U.S. was ground to 2 different particle sizes- 200 µm and 400 µm, respectively. Therefore, there were 3 different particle sized for the U.S. source (i.e., 200, 400, and 600 µm).

Five diets containing each source of field peas as the sole source of P were formulated. A total of 50 barrows (16.36 kg; SD = 1.19) were used and allotted to a randomized complete block design with 5 diets and 2 blocks of 25 pigs, 5 pigs per diet in each block, and a total of 10 replicates per diet. The weaning group was considered the blocking factor. Pigs were housed individually in metabolism crates. The initial 5 days were considered the adaptation period to diets, and fecal samples were collected quantitatively for 4 days following the adaptation period. Diets, ingredients, and fecal samples were analyzed for Ca and P to calculate the ATTD of P and Ca in each diet. The STTD of P was calculated by correcting the ATTD of P with the basal endogenous loss of P (i.e., 190 mg/kd DMI; NRC, 2012). Statistical model included diet (i.e., 5 different sources) as fixed effect and block as random effect and contrast statement was also used to test the linear effects of particle sizes. Results were considered significant at *P* ≤ 0.05 and considered a trend at *P* ≤ 0.10.

**Results**

Phosphorus and Ca intakes, Ca and P excretion (g/d), Ca and P absorption, the ATTD of P, the STTD of P, and the ATTD of Ca were not affected by different sources of field peas or different particle sizes (Tables 1 and 2). Concentrations of Ca and P in feces were greater (*P* < 0.05) if pigs were fed the diet containing the U.S. source with the particle size of 200 µm than if pigs were fed the diet containing the U.S. source with the particle size of 600 µm. However, concentrations of Ca and P in feces were not different among 4 sources of field peas with the particle sizes of 200 and 400 µm.

In conclusion, it is not likely that the STTD of P was not affected by different sources of field peas from different origins and by different particle sizes.

**Key points**

- Concentration of P in feces is reduced if particle size of field peas is 600 µm compared with 200 µm, but the STTD of P is not affected by particle sizes.

**Table 1. **Effects of different sources of field peas and different particle sizes on apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of P.

^{a-b }Means within a row that do not have a common superscript tend to differ (*P* < 0.05).

^{1}Data are least squares means of 10 observations per treatment. Except for U.S. 400 µm (*n* = 8).

^{2}EPL = endogenous P loss. Values were calculated as basal EPL (190 mg/kg DMI; NRC, 2012) × dry matter intake (kg/d DM).

^{2}Values for the STTD of P were calculated by correcting the ATTD of P with the basal endogenous loss of P.

**Table 2.** Effects of different sources of field peas and different particle sizes on apparent total tract digestibility (ATTD) of Ca in experimental diets^{1}

^{a-b }Means within a row that do not have a common superscript tend to differ (*P* < 0.05).

^{1}Data are least squares means of 10 observations per treatment. Except for U.S. 400 µm (*n* = 8).