Herbage yield and nutritive value of ten varieties of elephant grass, pennisetum purpureum, in Ashanti Region of Ghana

Six experiments were conducted to evaluate the nutritive value of nine hybrid Pennisetum and a local Pennisetum purpureum grown in the Ashanti Region of Ghana. The hybrid varieties were: 15743, 16786, 16791, 16798, 16834, 16835, 16837, 16838 and 16840 obtained from International Livestock Research Institute (ILRI.), Ethiopia. In the first experiment, agronomic characteristics of these varieties were measured at 56 days of regrowth. Parameters measured were plant height, bunch diameter, leafiness, stem diameter, tiller number, herbage yield and persistence. In the second experiment (intake studies), one hundred West African Dwarf Sheep (WADS) weighing between 9kg — 20kg were randomly allocated to ten treatments balancing for weight and sex. Grasses harvested each morning and chopped into short lengths were fed to each animal and feed refusals weighed back the following morning to determine intake. Adaptation period of 14 days was followed by 22 days of data collection for each animal. In the third trial (metabolism studies), eight WADS weighing 12 — 19 kg were used in a change over experiment. Feed intake, faecal output and urine volume was measured to determine apparent digestibility coefficient and nitrogen balance. Ten days adaptation was allowed followed by seven days collection period for each round. Degradability studies were conducted in the fourth experiment. Four rumen-fistulated rams were used in a completely randomised design. Grass samples collected during intake and metabolism studies were used for incubation at 3, 6, 12, 24, 48, 72, 96 and 120 hrs. In the fifth experiment grass samples collected during intake and metabolism studies were used for gas production. About 200 mg of each sample and 30 ml of rumen fluid media mixture was injected into syringes (incubation tubes) and incubated in lots of four in water-bath. Gas produced was recorded at 3, 6, 12, 24, 48, 72, 96 and 120 hrs respectively. Each of the Pennisetum varieties and their fractions were anyalysed for their content of crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL). Urine and faecal nitrogen were also determined Measurements of agronomic characteristics indicated that the DM yield was significantly (P<0.05) higher in variety 16840 had 1948.55kgha1 while variety 15743 had the lowest, 496.06 kg/ha. The bunch diameter was significantly (P<0.05) greater for the local variety than the rest, which ranged from 20.3 to 50.7 cm. Tiller numbers ranged from 12 to 25 and variety 16838 was significantly (P<0.05) higher in tiller number than the local. Varieties 16791 and 16835 were significantly (P<0.05) taller than both the local and variety 16840. The plant height ranged from 57.57 cm for variety 15743 to 189.98 cm for variety, 16791 which were significantly (P<0.05) different. The leaf fractions were significantly (P<0.05) greater in varieties 15743, local, 16837 and 16786 than the rest. There were significant differences with respect to persistence. The local variety ranked highest and was significantly (P<0.05) better than 16840 and the rest. The chemical composition of the grasses showed that the CP levels in the whole plant ranged from a low of 7.7% in variety 16791 to a maximum of 13.2% in variety 15743. The NDF concentrations were between 64.3% for variety 15743 to 73% for variety 16786, while ADF concentrations did not show wide variations. The values ranged from 37.3% to 45.3% for varieties 16798 and local respectively. The ADL concentrations in the whole plant were least in varieties 16838, 15743 and 16837 (0.85, 0.87 and 0.87%) respectively. ADL concentrations in the leaf and stem fractions also varied. The dry matter intake per metabolic body size ranged from 62.78 to 80.41g kg-1 per day. Dry matter intake of varieties 16838 and 16786 were significantly (P<0.05) higher than varieties 16840, local, 16837 and 16798 while variety 16791 was least consumed. The apparent DM digestibilities of the local variety and varieties 15743, 16840 and 16838 (69.53%) were also significantly (P<0.05) higher than the rest. Rumen degradation often varieties using samples from intake studies did not differ significantly (P>0.05) between the varieties at 48 and 72 hours of incubation. Differences, however, existed among the treatments during the rest of the incubation periods. There were no significant (P>0.05) differences between degradation constants for samples used during intake studies. Dry matter loss from 3 hours to 120 hours ranged from 181g kg-1 to 600g kg-1 Rumen dry matter degradation using digestibility samples ranged from 90g kg-1 (3 hrs) to 736g kg-1 (120 hrs) for varieties 16798 and 15743 respectively. Dry matter losses were significantly (P<0.05) affected by incubation time periods, except at 48 and 72 hrs for digestibility and intake samples. Significant (P<0.05) differences were obtained for degradation constants (a, b, (a+b)) for samples used during digestibility studies. In vitro gas produced at 3, 6, 12 and 48 hrs was not significantly (P>0.05) different using samples from digestibility studies. The volume of gas produced did not differ significantly (P>0.05) for each of the incubation periods when samples of intake studies were used. Similar non-significant relationship was’ obtained for samples used during intake studies except for the potential gas production (P<0.05). In the metabolism studies, dry matter in take per metabolic body size was significantly (P<0.05) affected by the type of grass fed to the sheep. Varieties 16837 and 16786 were significantly (P<0.05) higher in dry matter intake than the rest. The least consumed were varieties 16791, 15743 and 16835. The nitrogen intake ranged from 3.89g kg-1 for variety 16835 to 10.57g kg-1 for variety 16837. Faecal nitrogen excreted ranged from 1.79g kg-1 for variety 15743 to 3.14g kg-1 for variety 16837 while urinary-N ranged from 1.18g kg-1 for variety 16791 to 3.34g kg-1 for variety 16786. The nitrogen balance was positive for all the varieties with the lowest from 0.60 for variety 16835 to 5.29 for variety 16837. The relationship between feed intake and apparent digestibility coefficient of dry matter was not significant (r = 0.292). The correlation between feed intake and dry matter degradability from 3 to 120h incubation were not significant (P>0.05) at all incubation hours except at 6h (r= -0.320; P>0.05). However, the correlation between apparent digestibility coefficient of dry matter and dry matter degradability was significant at 96 and I20h (r = 0.371; r = 0.440; P<0.05) but not the rest. At 3h of incubation, significant (P<0.05) relationship was obtained between apparent digestibility coefficient of dry matter and in vitro gas production and not the rest of incubation hours. There was significant correlation between in vitro gas production and dry matter degradation using intake samples at 24h (r = 0.321; P<0.05). Significant relationship (P<0.05) was obtained between yield and other agronomic characteristics measured. Relationship between feed intake and chemical composition were not significant (P>0.05) while apparent digestibility and ADF were related (r = -0.660).

Source: KNUST