Promising tropical grasses and legumes as feed resources in Central Tanzania II. In sacco rumen degradation characteristics of four grasses and legumes

An in vitro gas production experiment was completed to determine effects of four tropical browse legumes (i.e., Acacia cornigera, AC; Albizia lebbekoides, AL; Enterolobium cyclocarpum, EC; Leucaena leucocephala, LL) at 0.15 or 0.30 of total substrate on microbial fermentation of the tropical grass Pennisetum purpureum CT-115 (PP). Two incubation runs with four bottles per treatment were completed, using two bottles for gas production measurements up to 96 h and two bottles for microbial purine bases (PB) concentration analysis after 24 h. Inclusion of AC, EC and LL linearly increased (P<0.05) gas production from PP alone at an initial stage of fermentation (5 h) because of their higher fermentation rate versus PP. However, whereas the linear increase in gas production was maintained at mid fermentation (i.e., 24 h) with AC, there was no effect with LL and a linear reduction in gas volume at 24 and 96 h with EC, possibly because of its saponin content. Gas production with AL was linearly reduced at 24 and 96 h (P<0.01). There were no differences in microbial concentrations, either estimated from a partitioning factor or PB analysis, but PB concentration in the solid residue increased three-fold when LL were included. Differences among legume species in chemical composition, and in the nature of their secondary compounds, are responsible for the fermentation pattern of mixed substrates.

Degradation characteristics of crude protein (CP) and metabolisable protein (MP) of feeds for early-weaned, growing and finishing beef bulls were evaluated in three experiments. Feeds in experiment 1 were fresh elephant grass (FEG) and molasses supplemented with sweet potato vines (SPV) in diet 1, supplemental (GCM) compounded from gliricidia, cottonseed cake (CSC), maize bran and NaCl in diet 2 and a commercial concentrate (CC) in diet 3. Feeds in experiment 2 were basal maize stover mixed with molasses (MSM) and FEG supplemented with SPV in diet 1, GCM in diet 2 and CC in diet 3. In experiment 3, MSM and FEG were supplemented with compounded supplemental protein feeds with varying levels of gliricidia inclusion. Supplemental (GM) containing gliricidia, maize bran and NaCl were used in diet 1, GCM in diet 2 and supplemental (CM) containing CSC, maize bran and NaCl in diet 3. Degradabilities of experimental feeds were measured at 0, 6, 12, 24, 48, 72, 96, and 120 h by the nylon bag technique using two rumen fistulated steers (300±10 kg). Effective CP degradabilities of FEG in the three experiments varied (P<0.05) with the supplements. In experiment 1, effective CP degradabilities of the supplements varied (P<0.05) from 668.3 g kg⁻¹ CP in CC to 722.1 g kg⁻¹ CP in SPV and 743.7 g kg⁻¹ CP in GCM. Effective rumen degradable protein (ERDP), digestible udegradable protein (DUP) and MP varied (P<0.05) among the supplements. In experiment 2, effective CP degradabilities of the supplements did not vary but ERDP varied (P<0.05) from 83.7 g kg⁻¹ CP in SPV to 116.6 g kg⁻¹ CP in GCM and 123.8 g kg⁻¹ CP in CC and MP followed similar trends. In experiment 3, effective CP degradabilities of the supplements decreased (P<0.05) with increasing gliricidia inclusion. ERDP increased (P<0.05) with lower gliricidia while DUP varied (P<0.05) from 18.2 g kg⁻¹ CP in CM to 23.6 g kg⁻¹ CP in GCM and 36.6 g kg⁻¹ CP in GM. These data have shown that the majority of locally available feeds evaluated in this study are not similar in CP degradation characteristics and MP but compounded GCM is more suitable in providing degradable and undegradable protein for beef bulls in Uganda.

An experiment was conducted to study the effect of increasing feeding level on digestibility and voluntary intake of four high yielding grasses cut at 6 and 10 weeks. The grasses were fed to Blackhead Persian rams (mean age = 72 weeks; mean weight = 30 kg) at levels of 600, 900, 1200, 1500 and 1800 g of hay per day in a split plot design. The grasses were Cenchrus ciliaris cv. Biloela (CCB), C. ciliaris cv. Gayndah (CCG), Panicum coloratum cv. Bambatsi (PCB) and Chloris gayana cv. Mpwapwa (CGM). In vivo organic matter (OM) digestibility was on average 60%. Among the species compared, CCB and PCB had lower OM digestibility, by 3 units, than CCG and CGM (P < 0.05), but CGM had lower intakes (P < 0.05) than the other species by approximately 20%. Samples taken at 10 weeks regrowth had higher neutral detergent fibre (NDF) and lignin contents and lower protein contents and in vitro organic matter digestibility compared to the 6-week cuts. Intake of OM, but not of NDF was also lower (P < 0.05) for the 10-week cut. The sheep consumed the grasses selectively in favour of the more nutritious parts when offered excess feed. With higher feeding levels, OM digestibility, but not NDF digestibility, was significantly improved (P < 0.05). Voluntary intakes of all species and stages were also improved by increasing feeding levels (P < 0.05). The lowest levels of feeding, allowing maximum intakes of the hays, varied between species and stages of maturity. These feeding levels ranged from 900–1500 g of hay per day with refusals between 15.3–50.8% for PCB (6 weeks) and CGM (10 weeks), respectively. From calculations of optimal feeding levels to attain maximum daily nutrient uptake by producing sheep, we recommend early harvesting and feeding of the grasses at levels allowing refusals of at least 30%.