Comparison of intake and digestibility of fresh Digitaria decumbens grass fed to sheep,indoors or at pasture,at two different stages of regrowth

The effect of two feeding systems (indoors and at pasture) on intake and digestion of fresh grass was studied at two stages of regrowth (21 and 35 days of regrowth) in two parallel experiments. In Experiment 1, 10 adult Martinik rams weighing, on average, 50.5 (±0.9) kg, including four fitted with rumen cannula, were randomly allocated to two groups according to a 2 × 2 Latin Square design. These rams consumed a 21-day regrowth of Digitaria decumbens grass diet during two successive 28-day periods, indoors (five rams) or at pasture (five tethered rams). In Experiment 2, 10 other Martinik rams weighing, on average, 45.5 (±0.9) kg, including four fitted with rumen cannula, were randomly allocated to two groups according to a 2 × 2 Latin Square design. These rams consumed a 35-day regrowth of D. decumbens grass diet during two successive 28-day periods, either indoors (five rams) or at pasture (five tethered rams). For the indoors groups, in vivo organic matter digestibility (OMD) was measured by total collection of feces. In addition, OMD was estimated indoors and at pasture using the fecal CP (CPf) method (OMD_CPf). Organic matter intake (OMI) was then estimated using OMD_CPf and fecal organic matter output (OMI_CPf). Correlations of 0.49 and 0.77 were found between in vivo OMD and OMD_CPf (P < 0.05) and between OMI and OMI_CPf (P < 0.001), respectively. OMD_CPf was 1.8% (P < 0.05) and 2.7% (P < 0.01) lower indoors than at pasture at 21 and 35 days of regrowth, respectively, whereas OMI_CPf indoors was 1.1 and 1.16 times that registered at pasture at 21 and 35 days of regrowth, respectively. The higher OMD_CPf at pasture was linked to the higher selective behavior of rams at pasture, whereas the differences in OMI_CPf between the two feeding systems were linked to differences in the total bulk density of the grass. These studies show that differences in OMD_CPf and OMI_CPf exist between animals fed indoors and at pasture with the same forage and that these differences may vary according to the stage of regrowth of the grass offered.