Phytate is a storage form of phosphorus in cereal grains and oil seeds, and has been known as an anti-nutritional factor in swine and poultry diets. Phytate binds not only to dietary cations such as copper, zinc, calcium, iron, magnesium and manganese, but also protein, fat and vitamins, thereby resulting in potential reductions in availability of these nutrients. Because pigs poorly utilize the phytate phosphorus in most diets due to their lack of enzymes to break it down, supplementation of phytase to the diet may be a useful means to enhance utilization of these non-phosphorus nutrients by degrading the phytate. Liberation of calcium, zinc and other nutrients such as fat and proteins resulting in increased availability of these non-phosphorus-nutrients has been demonstrated in some previous research.
Most of the phytase research for pigs has used low-phosphorus or phosphorus-deficient basal diets to confirm how much phosphorus is released from phytate to satisfy the phosphorus need of animals. However, using low-phosphorus or phosphorus-deficient diets does not allow investigators the ability to determine the extent to which any benefits might be from the phosphorus release or from other nutrients liberated when the phytate is broken down.
Further responses to phytase supplementation of the diets beyond phosphorus release are called “extra-phosphoric effects” such as enhanced macro- and trace-mineral availability and enhanced digestibility of amino acid and energy. These extra-phosphoric effects are usually associated with phytase supplementation at “super-dosing” levels which are defined as the use of unconventional high doses of phytase to degrade all, or the majority of, phytate and remove its anti-nutritional effects. Because super-dosing phytase supplementation is a concept to remove all six phosphate molecules by full destruction of phytate, it improves availability of not only the phosphorus, but also other nutrients (protein, fat, starch, vitamins and minerals) that might have been bound to the phytate.
Therefore, the improvements in performance with super-dosing phytase supplementation may result from a multitude of possible effects within the gastrointestinal tract.
An objective of this study was to evaluate the effect of graded supplementation of phytase on growth performance, carcass characteristics and apparent total tract digestibility (ATTD) in corn-based diets containing high-fiber byproducts such as corn distillers dried grains with solubles, wheat middlings and corn germ meal.
A total of 45 crossbred growing pigs (27 barrows [three replicates] and 18 gilts [two replicates]; mean initial BW = 26.4 ± 0.2 kg) were blocked by sex and birth weight, and randomly assigned to dietary treatments. The pigs were housed in individual pens in an environmentally controlled research facility. Feed and water were provided ad libitum. Dietary treatments included increasing phytase supplementation levels (0, 500, 1,000 and 2,000 FTU phytase per kilogram diet) in a basal control (NC) diet along with a higher-energy positive control (PC) diet. The basal diet met or exceeded all National Research Council nutrient requirement estimates including phosphorus. Diets were formulated in four dietary phases based on BW (Phase 1, 25-50 kilograms; Phase 2, 50-75 kilograms; Phase 3, 75-100 kilograms; Phase 4, 100-125 kilograms, respectively), and 0.30% titanium dioxide was added in the Phase 4 diets as an indigestible marker for ATTD determinations.
Body weight and feed consumption were recorded for calculation of average daily gain, average daily feed intake and gain-to-feed ratio. For ATTD estimation, fecal collection was performed for three consecutive days during Phase 4. All feed and fecal samples were analyzed for dry matter, gross energy, nitrogen, ether extract, neutral detergent fiber, acid detergent fiber, calcium, and phosphorus and titanium. The ATTD was calculated by the indirect method using TiO2 as an indicator. At a BW of about 120 kilograms, pigs were scanned by real-time ultrasound by an experienced technician, and backfat thickness and longissimus muscle (LM) depth were measured. LM area was estimated from the LM depth for each pig. The percent of carcass lean was estimated from back fat thickness and LM depth. Carcass daily lean gain was estimated by subtracting the initial lean for each pig from the final lean, and then dividing by the number of days on test. The weights of initial and final lean were calculated from National Pork Producers Council equations.
Data on growth performance, carcass characteristics and ATTD were subjected to analysis of variance using the general linear models procedure in statistical analysis system with a randomized complete block design. The individual pig served as the experimental unit. The final BW and feed consumption were analyzed on both a common weight and a common age basis to assess potential differences between data using the same feeding duration (common age) and using a common end weight (different days on test but analogous to feeding to a common market weight).
The ADG (P < 0.01, quadratic) and G:F ratio (P < 0.05, linear) for the overall period increased as phytase levels increased. Carcass lean percentage and lean gain increased (P < 0.05; linear) as phytase levels increased. The apparent total tract digestibility of DM, NDF, ether extract (P < 0.05) and hemicellulose (P = 0.05) increased quadratically as the phytase level increased. The ATTD of phosphorus increased as phytase supplementation levels increased (P < 0.05, linear and quadratic). These results demonstrated an improved nutrient digestibility, performance and carcass response to phytase supplementation beyond the phosphorus released by the phytase because all diets exceeded current phosphorus requirement estimates.
Increasing phytase supplementation level to grow-finish diets may lead to not only improved growth and nutrient utilization, but also increased carcass leanness, which could improve profit for swine producers. These responses to super-dose phytase supplementation may occur even when the diets contain adequate phosphorus. Therefore, using a high level of phytase in grow-finish diets may shorten days to reach market weight, reduce nutrient losses to manure and improve market price for pigs marketed on carcass lean percentage.
Researchers deduce that producers will benefit in improved feed efficiency and digestibility of nutrients. When phytase was supplemented at 1,000 FTU per kilogram diet, there were improvements of 8.8% of ADG and 5.0% of feed efficiency compared to the control diet, respectively. Additionally, the ATTD of DM, ether extract, NDF, hemicellulose and phosphorus increased at 1.3, 9.8, 2.9, 3.5 and 8.8 percentage units, respectively, when phytase was supplemented at 1,000 FTU per kilogram diet.
Carcass leanness also increased 1.6 percentage units when phytase was supplemented at 1,000 FTU per kilogram diet.
Researchers: Merlin D. Lindemann and Young Dal Jang, University of Kentucky Department of Animal and Food Sciences. For more information, contact Lindemann at 859-257-7524 or [email protected]. Researchers express appreciation to the National Pork Board and to AB Vista Feed Ingredients for support of this research project.