Abstract
This study was designed to measure the effect of regrowth age of Digitaria decumbens (D. decumbens) on the intake and dynamics of digesta in the rumen of rams. Six Black-belly rams (mean liveweight: 51.6 (s.d. 0.68) kg) fitted with rumen cannulae were fed twice daily a 14-, 28-, 42- and 56-day old fresh D. decumbens successively for 4 experimental periods. The daily dry matter intake decreased curvilineary from 75.2 to 48.5 (s.e. 2.0) g/kg BW 0.75 as the age of the D. decumbens grass increased from 14 to 56 days. Dry matter intake for the first 3 h after the morning meal was 863.6, 598.3, 576.4 and 401.5 (s.e. 55.6) g for the 14-, 28-, 42- and 56-day old grasses respectively. The pool of NDF in the rumen at the end of the 3-h feeding period did not vary significantly among the four diets. Twelve hours after the beginning of the morning meal, the pool of NDF increased with the forage regrowth age. Within the total pool of NDF, the pool of large particles tended to increase with the regrowth age. It was concluded that high intake was associated with fast evacuation ofNDF from the rumen. Moreover, digestion (cellulolysis) rate and degree of particle reduction by rumination are highly correlated, though speed of physical degradation of forage seems to be the driving force behind intake.
Highlights
Fresh forage is often the sole component of the diet of many ruminants in the humid tropics. Minson (1990) and Aumont et al (1995) recognised that voluntary intake is a major factor limiting the nutritional value of tropical forage
Diet composition and intake The composition and intake of D. decumbens are reported in Table 1 and 2
The daily intake decreased curvilineary with regrowth age according to the following equation: DMI = 82.4-1⋅379 days+0.0104 days2 (r2 = 0.82, SE = 5.2, n = 24, p
Summary
Fresh forage is often the sole component of the diet of many ruminants in the humid tropics. Minson (1990) and Aumont et al (1995) recognised that voluntary intake is a major factor limiting the nutritional value of tropical forage. Because of the very high level of fibre and the thickwalled bundle sheath of tropical grasses, Wilson (1994) and Archimède et al (2000) have hypothesized that in intensive systems, in tropical areas, where the forage is irrigated and fertilised, the low rate of reduction in size of large forage particles by chewing is the first limiting factor on intake, even with young forage This experiment was designed (i) to evaluate variations in tropical forage grass intake according to regrowth age, (ii) to study the digestion kinetics of fiber fraction in the rumen of rams, (iii) to study the impact of cellulolysis and physical breakdown of grass particles on intake. To take into account the fast growth of tropical forages, this study has been performed with grass with state of regrowth age within bounds larger than those classically studied
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