Estimation of Total Tract Apparent Digestibility of Nutrients in Three Annual Summer Forages Using Two Different Digestibility Markers

A study was performed to: 1) compare total tract digestibility of nutrients for three annual summer forages: Mulato II (hybrid Brachiaria); “Tifleaf 3” Pearl Millet (Pennisetum glaucum); and “Hay Day” Sorghum sudan (Sorghum bicolor) and 2) determine the efficacy of two digestibility markers: titanium dioxide (TiO2) and chromic oxide (Cr2O3) used with a fecal sample collection protocol of either 2 or 3 per d. Twelve Angus and Angus crossbred heifers were utilized in 6 pens within the Feed Efficiency Facility (FEF) in Marianna, FL. Heifers were fed daily fresh cuttings of one of the three treatment forages ad libitum. A GrowSafe System was used to determine feed intake which was used to evaluate dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) intake of heifers. There was no significant difference (P > 0.05) between the three forages for DM, OM, CP, NDF and ADF intake. No statistical difference (P > 0.05) was noted for total tract digestibility of the three forages. When evaluating markers and fecal collections, no differences (P > 0.05) were found between the different fecal collection protocols for TiO2; however, differences (P < 0.05) were found between Cr2O3 and TiO2 within the 2x sampling protocol. Also, differences (P < 0.05) were found between the 2x and 3x sampling protocols for Cr2O3. When comparing markers, one should consider using TiO2 as an indigestible marker instead of Cr2O3 to lower the chance of underestimation of digestion values. Titanium dioxide can be utilized along with fecal collections at 8:00 a.m. and 4:00 p.m. to sufficiently determine digestibility of summer forages. Introduction The digestibility of a feedstuff is a very good indicator of its nutritive value. Measuring digestibility allows researchers to determine the extent to which a nutrient is absorbed within an animal and, thus, decide how much of these nutrients are available for maintence, growth, reproduction, and production of protein such as milk and meat (Ibrahim and Olaloku, 2000). As it would imply, feeds with high digestibility have a tendency to have higher nutritive values, whereas feeds with low digestibility have a lower nutritive value (Kham et al., 2003). A livestock producer can potentially increase the efficiency of their operation by choosing forage varieties, grains or byproducts, based on the digestibility of the feedstuffs available for consumption by the animals.