Effects of super-dosing phytase in diets with adequate phosphorus on finishing pig growth performance and carcass characteristics

A total of 274 finishing pigs (PIC 1050 Ã— 327, initially 129 lb) were used in a 78-d study to compare the effects of adding high levels of three different sources of phytase (super-dosing) on growth performance and carcass characteristics of finishing pigs. Pigs were randomly allotted to pens with 7 or 8 pigs per pen and 9 replications per treatment. Dietary treatments included a corn-soybean mealâ€“based control diet that was formulated to meet the available P requirements of the pigs without any added phytase, or three diets that were formed by adding 2,000 FTU/kg of phytase from 1 of 3 different phytase sources to the basal diet. The three phytase sources were Quantum Blue 5 G (AB Vista, Chesterfield, MO), Ronozyme HiPhos (GT) 2500 (DSM Nutritional Products, Parsippany, NJ), or Optiphos 1000 (Enzyvia, Sheraton, IN). Overall, regardless of source, super-dosing phytase had no effect (P > 0.26) on ADG, ADFI, or F/G; furthermore, there were no effects (P > 0.36) on any of the carcass criteria measured. In conclusion, in this environment with nutritionally adequate diets, this study suggests that super-dosing phytase had no beneficial effects on finishing pig growth or carcass performance.; Swine Day, Manhattan, KS, November 21, 2013


Introduction
Phytase is routinely added to swine diets to improve phosphorus availability."Superdosing," or adding greater amounts of phytase to diets than that needed to meet the P requirement, has been suggested to elicit additional benefits above those attributed to the enhanced P availability.The hypothesis is that the phytase will improve digestibility and availability of other nutrients besides the P; however, previous research has not consistently demonstrated this benefit.Reasons for the inconsistency might be that different sources of phytase do not elicit the same response, differences in diet formulation (below or at the requirement), and differences in environment (university or commercial facilities).Therefore, the objective of this study was to determine the effects of superdosing phytase from three different phytase sources on finishing pig growth and carcass performance in university facilities.

Procedures
The protocol for this experiment was approved by the Kansas State University Institutional Animal Care and Use Committee.The study was conducted at the Kansas State University Swine Teaching and Research Center in Manhattan, KS.The barn

SWINE DAY 2013
was tunnel-ventilated with completely slatted flooring and deep pits.Each pen was equipped with a 2-hole stainless steel feeder and bowl waterer for ad libitum access to feed and water.Feed was delivered to each individual pen by a robotic feeding system (FeedPro; Feedlogic Corp., Wilmar, MN).
A total of 274 finishing pigs (PIC 1050 × 327, initially 129 lb) were used in a 78-d study with 7 or 8 pigs per pen and 9 replications per treatment.Pigs were randomly allotted to pen by initial BW and pens were assigned to 1 of 4 dietary treatments that were fed in meal form.The dietary treatments included a corn-soybean meal-based control diet that was formulated to meet the available P requirements of the pigs without any added phytase, or three diets that were formed by adding 2,000 FTU/kg of phytase from 1 of 3 different phytase sources to the basal diet.The three phytase sources were Quantum Blue 5 G (AB Vista, Chesterfield, MO), Ronozyme HiPhos (GT) 2500 (DSM Nutritional Products, Parsippany, NJ), or Optiphos 1000 (JBS United, Sheraton, IN).Diets were fed in 3 phases during the study, with 0.27, 0.23, and 0.21% available P formulated for Phases 1, 2, and 3, respectively (Table 1).Average daily gain, ADFI, and F/G were determined by weighing pigs and measuring feed disappearance every 2 wk throughout the study.
On d 78, all pigs were weighed and transported approximately 2.5 h to a commercial packing plant (Triumph Foods LLC, St. Joseph, MO) for harvest under USDA inspection.Before transport to the plant, pigs were individually tattooed according to pen number to allow for carcass data collection at the packing plant and data retrieval by pen.Hot carcass weight was measured immediately after evisceration, and each carcass was evaluated for carcass yield, backfat depth, loin depth, and percentage lean.Carcass yield was calculated by dividing HCW at the plant by final live weight at the farm before transport to the plant.Fat depth and loin depth were measured with an optical probe inserted between the 3rd and 4th last ribs (counting from the ham end of the carcass) at a distance approximately 3 in.from the dorsal midline.
Data were analyzed as a completely randomized design using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) with pen as the experimental unit.Differences between treatments were determined by using least squares means.Results were considered significant at P ≤ 0.05 and considered a trend at P ≤ 0.10.

Results and Discussion
Overall (d 0 to 78), no differences (P > 0.26) were observed between treatments for ADG, ADFI, or F/G (Table 2), and no differences (P > 0.36) were observed in HCW, carcass yield, backfat depth, loin depth, or percentage lean.When diets were formulated to meet the available P requirements of the pigs in this study, additional phytase from any of the sources did not benefit growth or carcass performance compared with the control.In conclusion, under the conditions of this study, superdosing phytase in diets formulated to be adequate in available P did not elicit additional benefits in pig performance.