Corn is the primary grain used in pig diets and provides most energy to the diets. Because energy is the most expensive component in diet formulation, it is critical to accurately determine energy concentrations in corn. Use of exogenous phytase in pig diets has been a standard and most phytase is expected to generate extra-phosphoric effects that result in increases in minerals, amino acid, or energy digestibility. Therefore, phytase companies have provided customers with matrix values that can be used for down specs of energy and nutrients in diet formulation. It is thus important to confirm if dietary phytase releases energy and other nutrients as suggested before using them. To our knowledge, however, there is no information on how much phytase can increase net energy (NE) 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 increased the apparent total tract digestibility (ATTD) of gross energy (GE) and concentration of NE by group-housed growing pigs.
Experimental design
Three diets were formulated. The first diet contained corn as the sole source of energy and this diet was a positive control (PC) diet. The PC diet contained Ca and P at the requirements for pigs (NRC, 2012). There were 2 negative control (NC) diets. First NC diet also included corn as a sole source of energy, but contained 0.08% standardized total tract digestible P and 0.12% total Ca less than the PC diet. 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 (weight: 45.0 kg) were housed in groups of 4 pigs in 6 indirect calorimetric chambers and allotted to 3 diets using a replicated 6 × 3 incomplete Latin square design with 6 chambers, 3 diets, and 3 periods. Each chamber was equipped with a slatted floor, 4 stainless steel fecal screens, and 2 urine pans for total, but separate, collection of fecal and urine materials. The temperature and humidity inside the chambers were controlled and maintained at the same levels in all chambers.
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 6 days on a time basis after 7-d adaptation. Total heat production (THP) was calculated using analyzed O2 consumption and CO2 and CH4 productions inside the chambers and N in urine. At 0700 h on d 14, pigs were deprived of feed for 36 h. This time was considered a fasting period to determine fasting heat production (FHP). Concentrations of digestible energy (DE), metabolizable energy (ME), and NE and the ATTD of dry matter (DM) and GE in diets and corn were calculated.
Results
Result indicated that feed intake, the ATTD of DM and GE, energy excretion in feces, urine, and heat, and NE did not differ among the 3 diets (Table 1). However, concentrations of DE and ME in diets and corn were less (P < 0.05) in the PC diet compared with the NC diet without phytase, but no difference was observed between the PC diet and the NC diet with phytase or between the 2 NC diets. Ratio between NE to ME was not different among diets, but ME to DE was increased (P < 0.05) by supplementation of phytase in the NC diets.
In conclusion, concentrations of DE and ME in corn are less if more feed phosphate and limestone are used in diets. However, concentration of NE was not affected by supplemental phytase or Ca and P levels, even though ME to DE was increased by supplemental phytase.
Key points
- The ATTD of DM and GE was not affected by Ca and P levels or supplemental phytase.
- Concentrations of DE and ME in diets were less if more feed phosphate and limestone were used in diets.
- Concentrations of DE, ME, and NE in corn were not affected by Ca and P levels or supplemental phytase.
Table 1. Concentrations of DE, ME, and NE in experimental diets and corn (n = 6)
a-bWithin a row, means without a common superscript differ (P < 0.05).
1BW = body weight.
