A comparison of two methods to assess nutrient digestibility in pigs

The noninvasive estimation of nutrient digestibility (DIG) is usually done by total collection (TC) of feces in balance crates or by the indicator method (IM) using an indigestible marker such as chromic oxide (CO). TC is precise but involves much labor. These methods were compared using pigs fed corn-soybean meal diets. In Trial 1, 10 pigs (68.1. kg) were individually housed in metabolism crates for a 5-day (d) TC. The IM phase immediately followed by adding CO to the feed for 2 consecutive d, and collecting a single grab fecal sample. In Trial 2, 24 pigs (66.2. kg) were used and Cr was fed for 7 consecutive d with single samples collected for 5. d starting when the stool color appeared bright green (which usually occurred on d3 after Cr was fed). Samples were composited into 5 final samples (d1, d1 + 2, d1 + 2 + 3, d1 + 2 + 3 + 4, d1 + 2 + 3 + 4 + 5) labeled D1, D2, D3, D4, and D5, respectively. In Trial 1, DIG values of DM, energy, and N were 2-3 percentage points lower for IM vs TC; DIG of Ca and P was 10-20 percentage points lower for IM. Differences related to dietary treatments were observed for 4 of these nutrients with TC but none of the nutrients with IM. In Trial 2, DIG by IM increased from D1 through D5, coinciding with increasing Cr excretion. For the macronutrients evaluated, all reached their DIG plateaus by D5 and similar values were observed between TC and IM. Dietary treatment differences were observed for Ca and P by TC and were also detected by IM. It is concluded that a multiday sample works better than a single grab sample for IM and that several days of marker observance are required before the marker content stabilizes in feces.