Evaluating dietary adjustment and collection times for total tract digestibility of Ca, P, and the essential microminerals with grower swine.

An experiment was conducted to determine 1) the length of time necessary for grower pigs to adjust to a new diet and 2) the consistency in excretion of urine and feces in 4 consecutive 5-d collection periods. The total tract excretion and digestibility values for Ca, P, and the essential microminerals were evaluated. The experiment was conducted in 6 replicates as a randomized complete block design. Pigs were fed a pretest diet from 20 to 40 kg BW that met the requirements. At 40 kg, 12 barrows were allotted to stainless-steel metabolism crates, where they continued being fed the pretest diet for a 7-d period for adjustment purposes. Treatment diets were then fed for the following 20-d period in four 5-d intervals. Treatment diets were a corn-soybean meal mixture and contained either 1) reduced Ca and P levels and no added microminerals (LOW) or 2) a diet with elevated Ca and P levels and supplemental microminerals that exceeded the pig's requirements (HIGH). The study collected urine and feces. Markers were added to the ration at the start of each period to distinguish between test intervals. Feces and urine were collected daily, frozen, and composited for each period. Analysis of diets and excrement was conducted using inductively coupled plasma mass spectrometry technology. In all cases, the excreted minerals and digestibility values were greater (P < 0.01) for the macrominerals when the HIGH diet was fed, whereas the digestibility values for the microminerals were often lower when the HIGH diet was fed. The macrominerals Ca and P both had consistent urine and fecal values for each of the final 3 collection periods within diet. The micromineral values were generally consistent for each 5-d collection period but varied between periods for several microminerals. These results indicate that a 5-d adjustment period was adequate for pigs to adjust to the treatment diets. A 5-d collection period was adequate for Ca and P, but the micromineral excretion and digestibility values were more variable, and a collection period of 10 d might be warranted. The results also indicated that the innate microminerals had a higher digestibility and bioavailability than thought previously and their digestibility is greater than that of inorganic microminerals. Thus, these results indicate that the innate microminerals should be an important factor in establishing the micromineral requirements for growing pigs. [ABSTRACT FROM AUTHOR]