Nutritive value of naturally growing Panicum glochiata and Panicum maximum in cool climatic areas of northern Malawi

M M Chiphwanya, F C Chigwa and H D C Msiska¹

Department of Animal Science, Lilongwe University of Agriculture and Natural Resources, Bunda Campus, P.O. Box 219, Lilongwe, Malawi
chiphwanya.maxwell@bunda.luanar.mw
¹ Department of Crop and Soil Sciences, Lilongwe University of Agriculture and Natural Resources, Bunda Campus, P.O. Box 219, Lilongwe, Malawi

Abstract

Panicum glochiata and Panicum maximum growing along streams and hydromorphic areas are the most preferred dry season feeds for feeding dairy cattle in northern Malawi. Forage samples were collected to monitor the nutritive value for potential to supply dairy cow requirements during dry season under the cut-and-carry system of production. Proximate components, gross energy, fibre fractions and in vitro dry matter digestibility were determined using standard laboratory procedures.

The results revealed a decline in crude protein content (82-52g/kg DM) and digestibility (498-383g/kg DM) and an ncrease in ADF (486-555g/kg DM) and NDF (771-882g/kg DM) when harvesting was delayed from June to October. In general, the two grasses accumulated more fibre fractions, dropped in crude protein and digestibility declined sharply. This reduced potential of grasses from barely meeting maintenance requirements to below survival. To complement this traditional practice, it would be advisable to grow improved forages and conserve them as hay so that enough quality feed is available during the lean months. On the other hand, resorting to making hay from natural forages, when they are still potentially nutritious, would also optimize nutrient composition and utilization.

Key words: cut-and-carry system, dry season, hay, in vitro digestibility, natural grass

Introduction

Smallholder dairy production substantially contributes to household food and income security in Malawi by providing consistent daily income (Tebug et al 2012). Smallholder dairy farming in Malawi is characterized by low inputs of a small herd size ranging from 2 to 4 cows. The majority of smallholder dairy farmers confine their dairy cows and practice zero-grazing throughout the year (Banda et al 2012). Zero-grazing requires a steady supply of high quality feeds to sustain milk production. Feed shortage during the dry season has been identified as a critical factor especially in the tropics and sub-tropics (Baur et al 2016). This stems from, among other reasons, high population pressure leading to less land allocated to improved pasture production which can be conserved for dry season. As a result farmers rely on harvesting forages from land not suitable for cultivation which are natural communal grasslands. However, rapid clearance of natural communal grasslands for crop cultivation as well as bushfires during dry season reduces the forage supply. In addition, natural forages precariously tend to be of low feeding value especially in the dry season. This is further compounded by some variation in rainfall pattern (Kasulo et al 2012) that negatively affects pasture production. Some areas in the northern region of Malawi experience cool climate with occasional precipitation during dry season that supports growth of grasses in dry season especially along perennial streams and hydromorphic areas. However these feed resources are not well characterized. This necessitates screening studies to evaluate feeding value of these naturally growing forages utilized by smallholder dairy farmers. This will complement earlier natural forage evaluation studies (Munthali and Dzowela 1985) since the choice of natural forages evaluated could not have been exhaustive. Evaluation of the nutritive value of natural forages is essential to provide a basis for development of adequate diets for dairy cows including the need for supplementation (Dierenfeld et al 2014). The study, therefore, aimed at monitoring the nutritive value of preferred natural grasses for potential to supply dairy cow requirements during dry season under the cut-and-carry system of production. The study intended to reveal nutritional gaps associated with the traditional cut-and-carry system and furnish information that would help farmers adopt strategies to offset potential nutrient gaps from natural forages.

Materials and methods

Study location

The study was conducted in the northern region of Malawi targeting smallholder dairy farmers clustered around Mzuzu city. Mzuzu city lies between latitudes 11^o 27ˈS-11^o 36ˈS and longitudes 34 ^o0ˈE-34^o17ˈE at an elevation of 1253m above sea level (www.mzuzu.climatemps.com). The area has humid subtropical mild summer climate with annual average temperature of 17.7^oC. The total annual precipitation averages 1388.6mm. Most rainfall is experienced between December to April peaking in March (averaging 222mm) with August recording the least averaging 8mm. Soils from primary production fields in the northern region belong to the sandy loams or sand textural class. Sandy clay loams are found in hydromorphic areas. Soil acidity is moderate becoming acidic (pH 4.0) where localized Oxisol soils occur (Snapp 1998). Typical grass species include Hyparrhenia spp., Panicum spp., Themeda spp., Andropogon spp. and Brachiaria spp. In addition, woody shrubs such as Tephrosia aequilata and Humularia descampsii are found (Reynolds 2006).

Study design and sampling natural grasses

Using extension workers and key farmers, two natural grasses preferred by smallholder dairy farmers for feeding dairy cattle were identified in three purposively selected milk bulking centers. The criteria for selection of the centers included activeness, registration to regional body, total membership and commitment of the members. The top two ranked forages were Panicum glochiata and Panicum maximum (hairy form, local ecotype). Forage samples were collected starting from the month of June, July, September to October, 2015. This period is dry season in Malawi when feed resources become critical. A total of 15 hand-grab sub-samples were collected by pacing along a 500 metre transect. The samples were pooled according to grass species and transported to the Animal Nutrition and Feed Technology Laboratory at Bunda campus, Lilongwe University of Agriculture and Natural Resources for further analyses. The sampling was repeated every month for four months.

Nutrient composition analysis of forage samples

All samples were first dried in an oven to constant weight then prepared by grinding using a Wiley Laboratory Mill to pass through a 1 millimeter mesh screen. Analysis for dry matter (DM) was determined by oven drying all samples at 105°C for 5 hours. Ash content was determined by igniting the dry samples in a muffle furnace at 550°C for 6 hours. Analyses for crude protein and ether extract were determined using methods described by AOAC (2002). Methods of van Soest et al (1991) were used to analyze fibre components of the forage samples, neutral detergent fibre (NDF) and acid detergent fibre (ADF), using the ANKOM ²⁰⁰ Fibre Analyzer (ANKOM Technology Corp., Fairport, NY). Gross energy content was determined in an oxygen bomb calorimeter (Parr 6100 Calorimeter, Parr Instrument Company, Moline, Illinois, USA). Finally, in vitro dry matter digestibility (IVDMD) was determined by the ANKOM technology method 3 using the DAISY^II Incubator (ANKOM Technology Corp., Fairport, NY).

Statistical analysis

The data was managed and analyzed in GenStat for Windows 17th Edition (VSN International 2014). Analysis of variance (ANOVA) using the General Linear Model was used as a statistical test in a completely randomized block design. Means were separated using the Pearson’s protected LSD at 95% confidence level.

Results and discussion

Seasonal changes in nutrient composition of natural forages

The results for nutrient composition are presented in Table 1 and illustrate the declining trend in CP content and IVDMD for Panicum glochiata and Panicum maximum as harvesting was delayed from June to October. On the other hand, fibre fractions and ash were increasing with delayed harvesting.

Crude protein content of Panicum glochiata and Panicum maximum significantly decreased at each sampling month from June to October (p<0.05). With delayed harvesting, grasses were progressively drying off. This is consistent with attainment of maturity stage as grasses develop physiologically from vegetative to reproductive phases hence increased stem fraction compared to leaf fraction. Stem elongation leads to accumulation of cell wall fraction which provides strength to the plant and less cell contents hence lowering leaf to stem ratio. Consequently, more mature grass has less cell contents than fibre. In addition, there is leaf shattering with advanced maturity. This is in strong agreement with earlier studies (Agza et al 2013; Ismail et al 2015) which reported a drop in CP content of natural forages with increasing stage of harvesting which was attributed to the decrease in leaf to stem ratio and the dilution of the nitrogen content by the increased structural carbohydrates. Similarly, Kubkomawa et al (2015) reported a remarkable decline in crude nitrogen content of Cenchrus biflorus. This characteristic Sahelian grass had a CP content drop from 160g/kg DM in growing plants during the rainy season to 40g/kg DM in foggage in November and only 26g/kg DM in foggage in April. However, van Soest (1994) reported that for a healthy rumen function ruminants require 75g/kg DM CP. For a lactating dairy cow the requirements rise to between 100 and 180g/kg DM depending on stage of lactation (NRC 2001; Moran 2009). Therefore, CP values recorded in this study hardly met the rumen microbial function requirements, and when lactation needs are factored in, delaying harvesting of the natural grasses only aggravated the protein deficiency problem. The cut and carry system is, therefore, unsustainable to furnish protein needs of a dairy cow.

The concentration of fibre fractions (NDF and ADF) significantly increased, in both grass species, when harvesting was delayed from June to October (p<0.05). This was due to accumulation of structural carbohydrates as the forages mature. Similar observations were reported by Tessema et al (2010) and Agza et al (2013) when natural forages were harvested at an advanced stage of maturity and this was attributed to increased cell wall lignification. However, NDF content in this study (770-880g/kg DM) is out of range (200-800g/kg DM) of forage dry matter weight reported by Wilson (1994), probably related to highly advanced maturity of forages in the present study. McDonald et al (2002) reported that tropical grasses have on average 660g/kg DM NDF content. At the same time, Singh and Oosting (1992) stated that feeds with more than 650g/kg DM NDF content were classified as low quality forages. Natural grasses evaluated fit in this category. This could affect the intake of the forages and limit production and productivity of dairy cows.

Regarding in vitro dry matter digestibility both Panicum glochiata and Panicum maximum significantly declined in digestibility (p<0.05). This drop became pronounced at the tail end in October. The findings are consistent with reports by Tessema et al (2010) and Agza et al (2013) when grass species were harvested at relatively advanced stages of growth. This was attributed to the deposition of lignin in the cell wall with increasing maturity and the increasing proportion of stem which becomes less digestible when compared with the leaf portion.

Trend of crude protein content and digestibility of natural grasses with advancement of dry season

Figures 1 and 2 describe the trend in crude protein content and in vitro dry matter digestibility of the natural grasses with time into the dry season. Crude protein content declined in both forages as season progressed. The trend line in figure 2 support this finding since digestibility is positively correlated to crude protein which represent the easily degradable fraction of the plant. Similar trends were also reported by Dzowela et al (1990).

Figure 1. Trend of crude protein content of natural grasses with time into the dry season

Figure 2. Trend of in vitro digestibility of natural grasses with time into dry season

Overall, when harvesting of the natural grasses was delayed from June to October, it was observed that the quality drastically dropped. When this is related to dairy cattle requirements, the forages are limited to supply needs particularly of lactating cows this becoming pronounced with delayed harvesting. The remedy is for farmers to grow improved forages and make hay to fill the nutrient gap in these critical months.

Conclusion

• The study concluded that harvesting forages from the natural grasslands, a norm under the cut- and-carry system, in most smallholder dairy farms, is not a sustainable practice to provide good quality and highly digestible feed in adequate amounts all year round.
  
  
• To complement this traditional practice, it would be advisable to grow improved forages and conserve them as hay so that enough quality feed is available during the lean months.

Acknowledgements

The Authors are grateful to European consortium under The Agricultural Research for Development, Dimension of the European Research Area (ERA ARD II) for financial support through “Developing and evaluating sustainable integrated farming systems for improvement of smallholder dairy production while optimizing crop production in milk shed areas of Malawi and Zambia (IFS SMADAP)” project. Further gratitude to project partners: Agroscope (Institute for Sustainability Sciences) of Switzerland and Institute for Agricultural and Fisheries Research (ILVO) of Belgium.

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Received 24 April 2017; Accepted 11 May 2017; Published 1 August 2017

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