By Fangzhou “Arkin” Wu, Mike Tokach, Joel DeRouchey, Steve Dritz, Jason Woodworth and Robert Goodband, Kansas State University
Appropriate dietary calcium and phosphorus levels are essential for nursery pig performance. Accurate formulation for calcium and phosphorus is even more important in recent years with the increased use of phytase and the desire to minimize phosphorus excretion.
Recent studies from the University of Illinois have suggested that feeding excess calcium in diets impairs phosphorus digestibility and, therefore, reduces growth performance of nursery and growing-finishing pigs. In common practices, diets can be in excess in calcium for multiple reasons, including variability in laboratory analysis of ingredients, neglect of calcium content in ingredients as a carrier, and not accounting for calcium being released by phytase.
Meanwhile, diets can also be deficient in phosphorus due to formulation errors, by phytase being mistakenly not included at expected levels in the diet, by overestimating the amount of phosphorus released for the given amount of phytase included in the diet, or by underestimating the pig’s requirements.
Therefore, we conducted this study to evaluate the growth performance and bone ash concentration of early nursery pigs in response to different combinations of dietary phosphorus and calcium levels provided by inorganic sources or phytase (1,000 FTU Ronozyme HiPhos 2500; DSM Nutritional Products Inc., Parsippany, N.J.).
In this experiment, 720 nursery pigs initially 13.4 pounds body weight were assigned to one of six dietary treatments in a 42-day study. Treatments were arranged in a 2×3 factorial design with two levels of calcium (0.58 versus 1.03%) and three levels of standardized total tract digestible phosphorus (STTD P; 0.33% without phytase, 0.45% without phytase, or 0.45% including phytase release of 0.12%).
The diet at 0.33% STTD P was approximately 27% under the estimated phosphorus requirement, while pigs fed at 0.45% STTD P were at the pig’s requirement. Experimental diets were offered from Day 0 to Day 28, and a common diet to all pigs was fed subsequently from Day 28 to Day 42 of the study.
Interactions between calcium and phosphorus treatments were observed (P < 0.05). From Day 0 to Day 28, when diets contained low calcium concentration, pigs fed 0.45% STTD P with phytase had greater (P < 0.01) average daily gain and average daily feed intake compared with those fed 0.45% STTD P without phytase and pigs fed 0.33% STTD P; whereas, when high calcium was fed, ADG and ADFI were similar among pigs fed 0.45% STTD P with or without phytase but were greater than those fed 0.33% STTD P (Ca × P interaction, P < 0.05).
Feed efficiency was impaired (P < 0.01) when low STTD P and high calcium were added to diets compared with other dietary treatments. From Day 28 to Day 42 when the common diet was fed, pigs previously fed 0.33% STTD P had similar ADG, but decreased (P < 0.05) ADFI and improved feed/gain compared with pigs fed 0.45% STTD P with or without phytase. However, pigs fed 0.33% STTD P with high-calcium diet were not able to fully compensate the negative effects of phosphorus deficiency resulting in decreased (P < 0.05) overall ADG and ADFI than pigs fed 0.45% STTD P diet with or without phytase.
In order to evaluate the effects of calcium and phosphorus levels on bone mineralization, we also determined the ash concentration of fibula bones from one sample pig from each pen. Pigs fed 0.33% STTD P had decreased (P < 0.05) bone ash concentration compared with those fed 0.45% STTD P with or without phytase when high calcium was added to diets, but this phosphorus effect was not observed when diets contained low calcium concentration (Ca × P interaction, P = 0.007).
In conclusion, excess calcium in diets impaired growth performance and bone mineralization of nursery pigs when diets were deficient in STTD P. Adding phytase to achieve 0.45% STTD P diets improved ADG and ADFI of pigs compared with diets containing 0.45% STTD P without phytase, indicating a potential underestimation of the phosphorus release from phytase or an increased availability of other nutrients liberated by phytase.