Until recently, rye has been less suitable for livestock feed than other cereal grains due to the risk of ergot contamination. However, recently developed hybrids are less susceptible to ergot contamination. There is limited information about the nutritional value of hybrid rye when fed to pigs.

In cereal grains, most of the phosphorus is bound to phytic acid, and is not available to pigs unless phytase is present. This is usually achieved by adding supplemental phytase, derived from microbes, to the diets. However, rye contains more intrinsic phytase than other cereal grains, so the phosphorus in rye may be more digestible. The addition of microbial phytase might also have less of an effect on phosphorus digestibility in rye than in other grains because of the high concentrations of intrinsic phytase in rye, but limited information about digestibility of phosphorus in rye has been reported.

An experiment was, therefore, conducted to test the hypothesis that the apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of phosphorus in hybrid rye is greater than in corn, barley, wheat, and sorghum, and to determine the effect of the addition of microbial phytase on ATTD and STTD of phosphorus in all cereal grains.

One hundred twelve growing barrows (13.7 ± 1.3 kg initial body weight) were fed a total of 14 diets. Seven diets were formulated based on one cereal grain, soybean oil, vitamins, and minerals. The cereal grains included three hybrids of rye - Bono and Daniello from Germany and Brasetto from Canada- and one source of barley, wheat, sorghum, and corn. All phosphorus in the diets originated from the cereal grains. Seven additional diets were formulated that were similar to the initial seven diets with the exception that they contained 1,000 units of microbial phytase. Feed intake was measured and feces were collected to determine the total tract digestibility of phosphorus.

The three hybrids of rye had intrinsic phytase activities ranging from 2,300 to 3,200 phytase units/kg. In comparison, the intrinsic phytase activity of wheat and barley was 580 and 490 phytase units/kg, respectively, and corn and sorghum both had less than 100 phytase units/kg intrinsic phytase activity.

The ATTD and STTD of phosphorus were greater (P < 0.05) in diets containing microbial phytase compared with diets without microbial phytase, with the exception of the diets containing wheat, in which there was no difference (Table 1). Daniello hybrid rye with microbial phytase had greater (P < 0.001) ATTD and STTD of phosphorus compared with all other cereal grains except barley. Daniello hybrid rye and Bono hybrid rye, without microbial phytase, also had greater (P < 0.05) ATTD and STTD of phosphorus than wheat and sorghum regardless of the amount of phytase in the diet. For diets containing microbial phytase, there was no difference in ATTD and STTD of phosphorus among barley, Bono hybrid rye, Brasetto hybrid rye, or corn.

• It is beneficial to include microbial phytase in  diets that contain rye, barley, corn, or sorghum due to the increased digestiblity of phosphorus observed with microbial phytase supplementation.
• Without microbial phytase, Daniello and Brasetto hybrid rye had greater STTD of phosphorus than barley, wheat, corn, and sorghum. This is probably because of the greater intrinsic phytase activity in rye.
• No differences in the STTD of phosphorus were observed among Bono hybrid rye, Brasetto hybrid rye, barley, and corn when microbial phytase was added to the diets.

Table 1. Daily feed and phosphorus (P) intake, apparent total tract digestibility (ATTD), and standardized total tract digestibility (STTD) of phosphorus in experimental diets

^a-i Means in a column without a common superscript differ (P < 0.05).

This report is based on unpublished research by Molly L. McGhee and Hans. H. Stein.