Comparative study of forage utilization between donkey and sheep.

Three forages - a mixture of good alfalfa and cooksfoot (50/50) hay (FLD), poor natural pasture hay (FP) and molassed wheat straw (PB), the contents of which were, respectively (DM%), 17.1, 9.2, 3.1 (CP) - 33.0, 34.1, 40.5 (CW) and 51.4, 66.5, 76.6 (NDF) - were given ad libitum, after being chopped, to six sheep and three adult donkeys weighing, respectively, 80 +/- 6 and 280 +/- 30 kg.LW. The intake and digestibility of the three forages were determined in vivo over three successive periods, each of which included 3 weeks of adaptation to the forages, followed by 10 and 6 days of measures, respectively, on the sheep and donkeys. Dry matter voluntary intake (DMI) decreased with the cell-wall contents of the forages in both species but to a greater measure in the sheep. With FLD, the DMI/kgW(0.75) were, respectively 62.8 and 85.2 g/day in the sheep and donkeys. Concerning FP and PB, the sheep ingested, respectively, 21 and 53% less as compared with the quantity noted with FLD. In the case of the donkeys, these decreases were only 4 and 30% for FP and PB, respectively. However, the DMI/kg.LW showed no significant difference between the two species when FLD was distributed. In both species, organic matter digestibility (OMD) varied inversely to the cell-wall content of the forage. With FLD (good hay) there was no significant difference in digestibility between the two species: 60.1 compared to 61.2%, respectively, for sheep and donkeys. FP and PB (poor roughages), on the other hand, showed significant differences (P < 0.001) between the two species of 4 to 6 points in favour of sheep; however, the important decreased of intake observed in sheep compels us to relativize these differences. In fact, digested energy expressed in digestible organic matter (IDOM) per kg of metabolic weight (W.(0.75)) was significantly higher in donkeys (P < 0001), which was even more evident as the forage was of poor quality. With FP and PB, donkeys ingested, respectively 14.7 and 10.4 g of DOM/kg.W-0.75 per day more than sheep. These observations show that the value of poor quality forages by donkeys to cover their requirements is more efficient than that for sheep.