Use of microbial phytase is common in diets for growing pigs because of the demonstrated effect of phytase to increase the digestibility of phosphorus and calcium. Sometimes phytase is also claimed to be able to increase energy digestibility and phytase companies sometimes provide customers with matrix values that can be used to down spec energy in diets for pigs. However, in many experiments researchers failed to demonstrate an increase in digestible energy and metabolized energy in diets containing phytase and it is, therefore, somewhat controversial if microbial phytase indeed increase the digestibility of energy.
Most energy balance experiments are conducted with growing pigs housed individually in metabolism crates, but on commercial farms, pigs are group-housed and share the same feeder within the same pens. To our knowledge, however, there is no information on effects of microbial phytase on energy digestibility in corn when fed to group-housed pigs.
Therefore, the objective of this experiment was to test the hypothesis that addition of microbial phytase to a corn-based diet increases the nitrogen balance, and therefore also the apparent total tract digestibility of gross energy, DE and ME by group-housed growing pigs.
Three diets were formulated. One diet contained corn (GE = 3,844 kcal/kg; dry matter = 88%) as the sole source of energy and this diet was a positive control diet. The PC diet contained Ca and P at the requirements for pigs (NRC, 2012). There were two negative control (NC) diets. One NC diet also included corn as the sole source of energy, but contained 0.08% standardized total tract digestible P and 0.12% total Ca less than the PC diet. The second NC diet was similar to the first NC diet with the exception that this diet contained 1,000 unit of phytase per kg diet.
A total of 24 pigs (initial body weight: 45.0 kg) were housed in groups of four pigs in six metabolism crates and allotted to three diets using a replicated 6 × 3 incomplete Latin square design with three diets and three periods for a total of six observations per diet. Each crate was equipped with a slatted floor, stainless steel fecal screens, and urine pans for total, but separate, collection of fecal and urine materials. Pigs were allowed ad libitum intake of feed and had free access to water at all time. Total feces and urine samples were collected for six days after seven days of adaptation. The ATTD of dry matter, GE and N, retention of N, and concentrations of DE and ME in diets and corn were calculated.
Results indicated that the ATTD of dry matter, the ATTD of N, retention of N, the ATTD of GE, and energy excretions in feces and urine did not differ among the three diets (Table 1). However, concentrations of DE ME in diets and corn were less (P P
In conclusion, N balance and concentrations of DE and ME were not affected by adding microbial phytase to a corn-based diet although ME to DE was increased by supplemental phytase. It was, therefore, not possible to confirm the hypothesis that microbial phytase will increase DE and ME in corn based diets fed to group-housed growing pigs.