Comparative analysis of the nutritional value and in vitro digestibility of different varieties of Napier grass within the smallholder dairy farming system in Kenya

Introduction

Smallholder farmers dominate the Kenyan dairy industry and rely on forage-based diets for their milk-producing cattle (Paudyal, 2024) [1] . The major fodder crop is Napier grass (Pennisetum purpureum) or elephant grass due to its high biomass yield and suitability to many agroecological zones (Staal et al., 2008) [2] . More recently, China's Pakchong Napier and Thailand's Juncao Napier Grass varieties have been introduced, along with the locally bred Kakamega 1 (KK1) variety, which exhibits higher biomass yields. These new varieties aim to improve the cost-effective feeding system for dairy cattle and alleviate auxiliary dependency on costly meals that cut into farmer profits. Dairy development policy has focused on alleviating low yields and poor-quality feeds among smallholder dairy farmers (Lukuyu et al., 2012). The need for these interventions comes at a time of increasing land resource pressures and the need for climate-smart agriculture as a strategy to mitigate climate change impacts (Kariuki et al., 2021) [3] . Enhanced biomass production per unit area achieved with improved Napier grass varieties can mitigate the land dairy production systems allocate for fodder crops and enhance efficiency (Goopy et al., 2020) [4] . In addition, the nutritional values of these new varieties may significantly improve the productivity of smallholder dairy farmers. It has been documented that the use of quality forages has a positive effect on the reduction of enteric methane emissions while improving milk production (Appuhamy et al., 2016) [5] . This dual advantage is in harmony with socio-economic and ecological protection objectives for the Kenyan dairy industry and other developing countries (Ndung'u et al., 2019) [6] . Also, very little is known about the newly released Napier grass varieties in terms of their relative nutritional value and degradation under Kenyan conditions. The goal of this research was to determine the nutritional values and In-vitro degradation of the three varieties to improve the nutritional and production decision-making process for smallholder dairy farmers.

Materials and methods

Grass cultivation and sampling

Under the same agronomic conditions within smallholder representative dairy farms in the highlands of Kenya, Pakchong Napier, Juncao Napier, and Kakamega 1 Napier grass varieties were grown and evaluated. The cultivation sites were chosen to capture the typical agroecological setup of the region with an altitude of 1500-2100 meters above sea level and an annual rainfall of 1000-1500 mm. The grasses were planted in randomized complete block design plots, each measuring 5m x 5m, with three replications per variety. Standard agronomic practices, including soil preparation, fertilization, and weed control, were followed. Nitrogen fertilizer was applied at 100 kg N/ha in split applications, with phosphorus and potassium applied based on soil test recommendations done recently by a reputable laboratory. Irrigation was provided as needed to ensure consistent growth across all plots. The grasses were allowed to establish for three months before the first harvest. Subsequent harvests were conducted at eightweek intervals to simulate typical smallholder management practices. Samples were collected at the same maturity stage, approximately 60 days after the previous harvest, when the grass height reached 1-1.5 meters. Sampling was done using a quadrat method, with three 1m 2 quadrats randomly placed within each plot. The grass was cut 15 cm above the ground to simulate grazing and promote regrowth. The harvested samples were immediately weighed for fresh biomass yield determination. Sub-samples of approximately 500g were then taken from each quadrat, chopped into 2-3 cm lengths, and thoroughly mixed. These sub-samples were dried in a forced-air oven at 65 °C for 72 hours to determine dry matter content. The dried samples were ground to pass through a 1 mm sieve using a hammer mill and stored in airtight containers for subsequent laboratory analyses.

Laboratory analysis: proximate and fiber assay of samples

The chemical composition of the grass samples, including dry matter (DM), crude protein (CP), crude fiber (CF), ether extract (EE), Metabolizable energy (ME), and ash content, was determined using standard methods (AOAC, 2005) [7] . The CP was calculated as Kjeldahl Nitrogen (N x 6.25). The fiber was analyzed according to the procedure described by Van Soest et al. (1994). Macro-elementspotassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), and micro-elements-copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe) were analyzed using an atomic absorption spectrophotometer (AAS). Samples were prepared by wet digestion using 1:1 nitric acid and 1:4 HCL for 30 minutes for ion dissociation.

Statistical analysis

Data collected on proximate and fiber analysis were subjected to analysis of variance (ANOVA) in a completely randomized design (CRD) using the general linear model procedure of statistical analysis system (SAS 2002) version 9.0. Significant means were separated using Tukey's HSD (Tukey's Honestly Significant Difference Test) at 5% significance.

The model used for statistical analysis was: Y_ij=μ+τi +εij where: Y_ij= is the j th observation of the i th treatment µ= is the population mean τi= is the effect of treatment εij= random error term

In vitro gas production

The milled samples of Pakchong Napier, Juncao Napier, and Kakamega 1 Napier grasses, weighing 200 mg DM of each, were placed in 100 ml glass syringes in triplicate. The fermentative activity of the mixed microbial population was determined using the gas production technique described by Menke and Steingass (1988). The rumen fluid and buffer medium were mixed in a ratio of 1:2 (v/v). Then, 30 ml of the buffer-rumen fluid mixture was passed into triplicate syringes holding samples and incubated in a thermostatically controlled water bath at 39 °C for 0-96 hours. The samples and blank (rumen fluid + buffer) were run in triplicate. Then, the volume of gas produced was determined at 0, 3, 6, 9, 12, 18, 36, 48, 72, and 96 hours by reading the calibration of the piston. The gas produced was the total increase in volume minus the mean blank value from the recorded gas production of all samples to give the net gas production. The calculated values of gas production were fitted into the model of Ørskov and McDonald (1979) [8] to determine the degradability of the feed:

Y=the volume of gas produced with time (t) a=initial gas production b=gas produced during incubation c= gas production rate constant (fraction /hour), and a+b represents the potential extent of gas production.

Results

Proximate composition

Mineral profile

Feeding and utilization

Table 3 shows a detailed breakdown of the supplementation levels and the type of supplementation needed for the three Napier grass varieties when used as a basal diet, with focus on Crude Protein (CP),

Metabolizable Energy (ME), and Minerals in small holder dairy production systems. [8] , showed the differences more clearly. Pakchong Napier also had the highest potential extent of gas production with 9.36, followed by Kakamega 1 Napier 6.64 and Juncao Napier 5.64. The greater value of these gas production and kinetic parameters for Pakchong Napier suggests it to be more digestible than Juncao and Kakamega 1 Napier. These results suggest that Pakchong Napier has a greater potential for rumen and nutrient degradability in relation to the livestock's needs.

In-vitro fermentation characteristics

Discussion

The superior nutritional value of Pakchong Napier over Juncao Napier and Kakamega 1 Napier is indicated by its higher crude protein and metabolizable energy contents, alongside lower fiber values. These results are in agreement with previous research focused on livestock nutritional needs, especially the uptake and performance benefits from feeding high-protein to low fiber diets (Jacovetti et al., 2023) [9] . Pakchong Napier appears to have a better potential in enhancing dairy cattle feed efficiency because of the higher fermentation characteristics it supports. The 17.7% crude protein value of Pakchong Napier is remarkable since it surpasses the 15% CP minimum value prescribed for lactating cows (NRC, 2001). This value in protein may lessen the financial deficits involved with protein supplementation in smallholder dairy systems, elevating cost efficiency and milk yield instead (Mutimura et al., 2018) [10] . Pakchong Napier's lower NDF and ADF also suggest improved digestibility, which is important in support of high dry matter intake in the dairy cows (Oba et al., 1999) [11] . The intermediate fermentation characteristics and crude protein content of 15.3% makes Juncao Napier an option for smallholder dairy farmers. It appears as though it could serve as effective forage, stating nutrition in regions where Pakchong Napier would not adapt well. However, with the lower protein value of 9.9% crude protein and Kakamega 1 Napier's slower fermentation rate, it may be necessary to supplement the diet with higher protein feeds to fulfill the daily nutritional needs. The analysis of the mineral composition revealed differences for the three samples being tested. Lactating cows could benefit greatly from lower mineral supplementation due to the higher concentration of calcium and phosphorus in Juncao Napier (Goff, 2018) [12] . His work regarding iron was supported by Spears et al. (2019) [13] , where the higher iron content in Kakamega 1 Napier further adds to his statement regarding these areas being beneficial in locations stricken with iron deficiency. The study on gas production in vitro also assisted in determining the fermentation kinetics of the three varieties of Napier grass. The improved cumulative gas production alongside the rate of fermentation in Pakchong Napier suggests an elevation in the completeness and rate of degradation within the rumen; therefore, increasing the nutrition and milk production of the animal. This supports the findings of Meale et al. (2012) [14] , demonstrating the correlation between Invitro gas production and the In-vivo digestibility of ruminants. The effective fermentation attributes of Pakchong Napier may affect methane production as well. Although not directly assessed in this research, faster fermentation rates are often associated with reduced methane yield per unit of feed intake (Jayanegara et al., 2017) [15] . This might help reduce greenhouse gas emissions associated with the dairy industry, which is a major issue in the context of climate change (Hristov et al., 2013) [16] . It is crucial to highlight that the in-vitro approach offers specific, valuable insights, but they may not fully represent the complex dynamics of the rumen environment. Passage rate, chewing time, and other dietary components may have an impact on digestibility and nutrient utilization in vivo (Huhtanen et al., 2006) [17] . Hence, while these results are promising, additional in-vivo research and feeding experiments are necessary to confirm the expectations of the superior performance obtained from Pakchong Napier as well as Juncao Napier on the actual farm conditions.

Conclusion and Recommendations

This research sheds new light on the nutritional values and the fermentation properties of Pakchong Napier, Juncao Napier, and Kakamega 1 Napier grasses for the smallholder dairy production systems in Kenya. The findings clearly show that Pakchong Napier has the highest nutritional quality and in vitro fermentation characteristics of all three Napier grasses, with a crude protein content of 17.7% and relatively lower fiber fractions than the other two Napier grasses. These qualities indicate that Pakchong Napier can substantially enhance the productivity of milk output and dairy farming in smallholder systems. Juncao Napier also shows promise as a high-quality, intermediate to the other two Napier grasses, and good mineral content, which makes this variety suitable in regions where Pakchong Napier may not thrive. Although the nutritional quality of Kakamega 1 Napier grass is relatively low, its adaptability to a wide range of agrological zones gives this grass a potential place in certain production systems, although needing protein supplementation. These findings highlight the potential of improved Napier grass varieties, particularly Pakchong Napier, to significantly enhance the productivity and sustainability of smallholder dairy systems in Kenya. Based on these findings, we recommend:

1. Implementing feeding trials to assess animal performance fed on the three varieties of Napier grasses on milk yield, milk composition, meat quality, and animal health in dairy cattle under typical smallholder management conditions in different agro-ecological zones.

2. Conducting on-farm trials to evaluate the field performance of Pakchong and Juncao varieties under different agroecological conditions, including their biomass yield, persistence, and resistance to pests and diseases.

3. Evaluating the long-term sustainability of these improved varieties, including their impact on soil health, water use efficiency, and greenhouse gas emissions from dairy cattle production systems.

4. Economic analyses should be conducted to quantify the potential benefits of adopting these improved varieties.

5. Investigating the ensiling characteristics of these Napier grass varieties to improve year-round feed availability for smallholder farmers.

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