Ecological benefits of brachiaria grasses in integrated crop-livestock production systems in Rwanda.

Abstract

A study was conducted with the broad objective to evaluate ecological benefits of Brachiaria grasses in integrated crop-stall-fed livestock production systems in humid and semi-arid region of Rwanda. The specific objectives of the study were: (1) To identify factors that determine household feed resource supply and willingness to plant improved fodder in humid and semi-arid regions of Rwanda; (2) To determine nutritive values of available feed resources used by smallholder farmers in Rwanda; (3) To determine biomass and nutrient productivity as well as cutting management of promising Brachiaria genotypes for semi-arid ecologies in Rwanda (4) To determine nutritional value of Brachiaria species, on stall-fed replacement dairy heifers with or without concentrate supplements; (5) To examine the biophysical and physiological basis that make Brachiaria grass a more palatable and nutritious forage with impact on lactation in dairy cows relative to Napier grass. A structured questionnaire was administered to 204 households of semi-arid and humid environments and used to determine major livelihood options and characterise integrated crop-livestock production systems. Farming was the major livelihood strategy among households in semi-arid and humid areas. The diversity of livestock species including, dairy cattle among households were more in semi-arid than in humid environments. Milk yield was higher in Jersey than in other dairy cows under smallholder farm prevailing conditions. Logistic regression analysis showed that age, level of education and experience in livestock rearing of household head significantly influenced adoption of planted forages in smallholder farms in both areas. Farmers in semi-arid area were twice more likely to establish improved fodder species in farmland than those from humid areas. Napier grass and a variety of crop residues were the major feed resources in both the rainy and dry seasons in both areas. Feed resource inventorying depicted a wide (n=24) species diversity from both on-farm and off-farm source five of which were unique to semi-arid areas. Chemical composition, ii contents of metabolisable energy (ME), organic matter digestibility (OMD) and neutral detergent fibre digestibility (NDFd) and rumen fermentation characteristics partitioning factor (PF) were highly variable, depicting variability in their efficiencies of utilisation in microbial functions and post-ruminal nutrient supply for maintenance and production. Brachiaria genotype and cutting management study involved an evaluation of five cultivars (cv.) of Brachiaria brizantha, one cultivar of B. humidicola, two cultivars of Brachiaria hybrid and one cultivar of Brachiaria decumbens against Napier grass (Pennisetum purpureum) in an on-farm trial in a completely randomised block design (RCBD) with four replicates. Forage samples were collected at 60, 90 and 120 days after planting (DAP). Samples of each cultivar and age of cutting were analysed for concentration of dry matter (DM), crude protein (CP), organic matter (OM), neutral detergent fibre (NDF), minerals, in vitro apparent degradable dry matter (ivADDM), metabolisable energy (ME) and in vitro gas production (GP) kinetics. The DM, CP, OM, ivADDM and digestible OM increased from 60 to 90 DAP and declined thereafter. The NDF contents increased while CP contents decreased consistently with increase in age. Macro and micro-nutrient concentrations were also higher at 90 DAP. The ME differed (P<0.05) among grasses and between DAP. The GP of grasses cut at 90 DAP was higher than the other two DAP. The highest yield cultivars were Basilisk, Marandú and Piatá. The optimum age of cutting was species specific, but overall cutting at 90 DAP was recommended. In a study on changes in growth performance of crossbred dairy heifers under cut-and-carry feeding system, sixteen crossbred (Ankole × Jersey) heifers (Average body weight 203±35 kg) were randomly allocated to two dietary treatments. Brachiaria hybrid cultivar Mulato II with 2 kg/day of commercial concentrates (MCC) and Napier grass (Pennisetum purpureum) with the same supplement (NCC) were fed to heifers for 12 weeks. Feeds, mineral lick and water were provided ad libitum. Absolute daily dry matter intake (g DM/day) and relative intake (g/kg of metabolic body weight - BW0.75) were higher in heifers fed on MCC than in heifers fed on NCC (P<0.001). Feed conversion ratio was lower (P<0.001) in MCC than NCC diets. Final body weight (FBW) and body weight gain (BWG) did not differ between the two groups of heifers (P>0.05). Average daily weight gain (ADWG), also not differed significantly (P>0.05). To determine biophysical factors affecting quality of Brachiaria sp. and impact on performance in crossbred dairy cattle, a feeding trial was conducted using 40 lactating crossbred (Ankole × Holstein Friesian) in second parity and in 10–15 days in milk in collaboration with 40 farm households. Experimental diets were Brachiaria brizantha (cv. Piatá) and Napier grass (Pennisetum purpureum–used as control) as sole or mixed forage with Desmodium distortum (70:30 w/w fresh basis). Chemical analysis showed that Napier was low in DM, OM, and CP, but higher in NDF and ADF than the test Brachiaria (P<0.001). The composition varied with duration of the experiments (P<0.05) but not across farms (P>0.05). Voluntary intake did not differ across diets (P>0.05) but was consistently higher in Piatá-based than in the Napier-based diets. Average milk production with higher in cows fed on the test Brachiaria-based than in the Napier-based diets (P<0.001). Cows fed grass-legume mixes recorded higher milk than sole grass diets. Digesta flows and degradation rates were also rapid in grass-forage than in sole grass diets (P<0.001). The most promising cultivars identified from this study were cv. Basilisk, cv. Marandú and cv. Piatá, because of its nutritional characteristics as well as nutrient yields which were higher and more comparable with Napier grass than other grass cultivars. The feeding trial with replacement dairy heifer proved that depriving these animals the nutritional advantage associated with selectivity in forages did not compromise the nutritional value cv. Mulato II; hence, this cultivar can effectively be used as quality fodder for cut-andcarry dairy system. Digestive physiology of Piatá-based diet provided a strong, but indicative evidence of the differences in palatability, voluntary intake and impact on lactation between cv. Piatá and Napier grass. These differences might have associated with physical effectiveness of NDF.