Fattening “Yellow” cattle on cassava root pulp, urea and rice straw: completely mixed ration system with cassava foliage as protein supplement compared with feeds not mixed and brewers’ grains as protein source

Phanthavong Vongsamphanh, T R Preston¹, Thansamay Vorlaphim², Dinh Van Dung³ and Nguyen Xuan Ba³

Department of Livestock and Fisheries, Ministry of Agriculture and Forestry PO Box 6644 Vientiane, Lao PDR
vongsamphanh2015@gmail.com
¹ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia
² Livestock Research Center, National Agriculture, Forestry and Rural Development Institute Vientiane, Lao PDR
³ Faculty of Animal Husbandry and Veterinary Medicine, Hue University of Agriculture and Forestry, Hue University, Hue City, Vietnam.

Abstract

The concept of the “Complete Mixed Ration” (CMR)” was evaluated as the basis of the method for incorporating cassava foliage as the protein-fiber source in a fattening system for local Yellow cattle based on ensiled cassava pulp (derived from processing of cassava roots for starch production). Ensiled cassava pulp was mixed with fresh cassava foliage and rice straw in fresh form the day prior to feeding (CMR); or ensiled during three weeks prior to feeding (ECMR). In both cases urea and minerals were added to the mixed rations at the time of feeding. The control system (CTL) was providing the feeds separately, in the same feed trough, with the cassava foliage replaced by brewers’ grains. Local Yellow cattle (n=15; mean live weight 160 kg) were housed in individual pens and fed for 90 days on each of the treatments.

Growth rates were 622 and 608 g/day when the diet of ensiled cassava pulp, supplemented with urea, cassava foliage, brewers’ grains and rice straw, was fed as a completely mixed ration in fresh form (CMR), or after ensiling for 21 days (ECMR). Live weight gains were 30% higher (857 g/day) when almost all the protein was in the form of brewers’ grains, and the ingredients were not mixed (apart from the urea which was dissolved in the cassava pulp at the time of feeding). Feed conversion rates were 8.85 and 9.14 for the CMR and ECMR systems compared with 6.61 for the control. It is suggested that excessively high levels of cyanogenic glucosides in the cassava foliage, which was collected at the end of the dry season from a “bitter” cassava variety at the time of root harvest, may have contributed to the poorer performance of the cattle fed the CMR diets.

Key words: bitter cassava, cyanogenic glucosides, ensiling, fumonisin, HCN, mycotoxins

Introduction

The commercial beef industry and beef value chain in Lao People’s Democratic Republic (Lao PDR) is relatively small and at an early stage of development (MAF 2016). Transforming cattle production from smallholder subsistence to more intensive systems using locally available byproducts from cassava starch factories is a recent development (Phanthavong et al 2014) that has potential widespread application There are five factories processing annually 1.6 million tonnes of cassava roots, of which some 15% remains in the form of cassava pulp. The system built around the cassava pulp as the basal feed resource (Phanthavong et al 2016a) used urea to provide the ammonia needed by rumen micro-organisms, brewers’ grains as the source of bypass protein and rice straw for fiber. On this system the growth rates of local Yellow cattle were close to 800g/day with a conformation after 90 days feeding indicative of quality beef grade (Photo 1).

Photo 1. Local Yellow cattle fattened for 90 days on cassava pulp-urea, brewers’ grains and rice straw

One of the challenges for extending the application of this fattening system has been to identify a local replacement for the brewers’ grains, which was the initial source of the bypass protein that plays a key role in supplementing the microbial protein derived from urea. The foliage from the cassava plant is the obvious first choice in view of the successful use of this protein source to supplement urea in a cattle-fattening system based on molasses-urea (Ffoulkes and Preston 1978).

The first attempts to use cassava foliage to supplement the cassava pulp-urea system were disappointing as feed intakes and growth rates were low (Phanthavong et al 2016b) apparently because the cattle were averse to eating the cassava foliage. It became apparent that the difference between the experiment of Ffoulkes and Preston (1978) in the Dominican Republic and the initial studies in Laos was related to the source of the cassava which was a sweet variety as grown for human consumption in the Dominican Republic (Ffoulkes and Preston 1978) compared with the “bitter” variety, which is used for commercial starch production in Laos. As the names imply, levels of the cyanogenic glucosides, which on digestion in the animal give rise to toxic hydrocyanic acid (HCN), are higher in bitter compared with sweet varieties (Sarkiyayi and Agar 2010; Phuong et al 2012). Important steps forward were: (i) the observation that cattle fed bitter cassava foliage had a “craving” to eat brewers’ grains (Phanthavong 2016, unpublished observations); and (ii) the “craving” was explained by the immediate improvement in growth rate (from 10 to 600 g/day) when 4% of brewers’ grains was fed alongside the bitter cassava foliage accompanying the basal diet of cassava pulp-urea (Binh et al 2017). It was shown that the brewers' grains apparently assisted in the detoxification of the HCN precursors in bitter cassava foliage, as reflected in reduced excretion of thiocyanate in the urine of the cattle fed the bitter cassava foliage (Binh et al 2017).

There are two altenatives for incorporating cassava  foliage in the feeding system: (i) growing cassava as a semi-perennial forage (eg: Preston and Rodriguez 2004; Phengvilaysouk and Wanapat 2008) with repeated harvesting ar 8-12 week intervals (Vivasane et al 2017) and feedng it in the fresh state withut processing (Keopaseuth and Preston (2917); or (ii)  preserving (or feeding directly) cassava leaves, petioles and fine stems collected immediately prior to root harvest (Photos 2-5).  It is estimated that the quantities of foliage available at root harvest are of the order of 1,200 tonnes annually.

Photo 2. The cassava field ready for root havest	Photo 3. Harvesting the foliage	Photo 4. The branch (tender stem, petioles and leaves) to be used as animal feed	Photo 5. Residual stems to be used for planting the next cassava crop

 The following experiment was set up to evaluate the system in which the cassava foliage was collected during the  time of root harvest.

Materials and methods

Location and duration

The experiment was carried out in Natthana Chok Farm, Xaythany District, situated some 30 km from Vientiane Capital, from 14 January to 14 April 2018.

Treatments

The three feeding systems were based on the ingredients described in Tables 1 and 2.

The treatments were:

CTL: The fattening system developed by Phanthavong et al (2016a), based on ad libitum ensiled cassava pulp-urea, fresh brewers’ grains (1% of live weight, DM basis) and rice straw (1 kg/day) (Table 1). The ingredients were given as separate feeds in the trough (without mixing).

CMR: All the diet components (Table 1) were mixed together 18-24h before feeding.

ECMR: The ensiled cassava pulp, cassava foliage, brewers’ grains and rice straw (Table 1) were mixed and ensiled in closed 100 liter plastic drums for 21 days prior to feeding.

For both CMR and ECMR, the urea, rice bran and minerals were added and mixed with the feeds immediately prior to feeding.

Animals

Fifteen female local Yellow cattle with average age 2 years and mean initial weight 160 kg were housed in individual pens. There were five animals on each of the three treatments in a completely randomized design. They were injected intramuscularly with Ivermectin (1ml/50 kg live weight) to control internal and external parasites.

Feeding system

The CMR diet was prepared daily, at about 3 pm, one day before being fed to the cattle. For the ECMR diet the ingredients were mixed and ensiled in closed 100 liter plastic drums for 21 days before feeding (Table 3).

The pH of the mixed feeds (ECMR and CMR) was taken after mixing, after 21 days of ensiling (for ECMR) and immediately after adding the urea and minerals prior to feeding (Table 4).

Midway through the experiment (after 45 days) samples were taken of the three diets prior to feeding and stored frozen prior to analysis for the mycotoxin "Fumonisin".

Measurements

The cattle were weighed before morning feeding at the beginning of the trial and every 14 days. Feeds offered and refused were recorded daily. After 90 days, at the end of the experiment, rumen fluid samples were taken by stomach tube prior to acidification with sulphuric acid for subsequent analysis of volatile fatty acids by gas chromatography (Samuel et al 1997) and ammonia by Kjeldahl digestion (AOAC 1990). DM and crude protein in feeds were analysed using the methods of AOAC (1990). Protein solubility was determined by the method described in Whitelaw et al (1961). Fumonisin levels in feed samples were determined following the method described by Pestkai et al (1994).

Statistical analysis

The data were analyzed as a Complete Randomized Design (CRD) using the general linear model in the ANOVA program of the MINITAB (2000) software. Live weight gains were determined from the linear regression of live weight (Y) on days in the experiment (X).

Results and discussion

Growth rates were decreased by 30% on the completely mixed rations compared with the control diet with feeds given separately (Table 5; Figure 1). Feed intake was similar on the three feeding systems with the result that the DM feed conversion ratio was also poorer on the CMR/ECMR diets. On all three feeding systems the offer level exceeded the intake by a margin of 14-19% but did not differ among feeding systems. Feed offered and not consumed is an economic loss unless the residues are fed to other animals.

Figure 1. Comparative growth rates and DM feed conversion of Yellow cattle fed ensiled cassava pulp-urea, and rice straw supplemented with brewers’ grains (CTL); or a completely mixed ration (CMR) of 46% ensiled cassava pulp, 26% fresh cassava foliage and 4% brewers grains (all on DM basis); or the completely mixed ration ensiled 3 weeks before feeding (ECMR). On all diets, urea and minerals were added immediately before feeding.

Molar proportions of acetate were lower and those of butyrate higher in rumen fluid from cattle fed the CTL diet compared with the completely mixed rations (Table 6). There was a tendency (p=0.10) for the acetate: propionate ratio to be lower in rumen samples from cattle fed the CTL diet.

Discussion

There was a major difference between the CMR and CTL diets in the sources of protein with cassava foliage (26%) and brewers’ grains (4%) in the CMR diets replaced by 30% brewers’ grains in the control diet. This is not thought to be the reason for the differences in performance as in a feeding trial with the same basal diets and breed of animals (but with feeds that were not mixed), there were no differences in live weight gain between treatments in which brewers’ grains were the sole source of protein (ADG 563g/d) compared with only fresh cassava foliage as protein source (ADG 528g/d) (Keopaseuth and Preston 2017). When cassava foliage was the sole source of protein in a cattle-fattening diet based on molasses-urea, there were no benefits from replacing 50% of the cassava foliage with soybean meal (Ffoulkes and Preston 1978).

The proportion of rumen-undegradable (or bypass) protein in brewers’ grains was determined by Promkot and Wanapat (2005) to be 59%, only slightly higher that in cassava hay (53%). These relative values can be compared with the solubility of the protein (Table 2) which was 34 and 30%, respectively for brewers’ grains and cassava foliage. Protein solubility is a good index of rumen protein bypass characteristics (Preston and Leng 1987).

There were only minor differences in the VFA pattern on the three diets (Table 6) and thus were unlikely to affect the energy status of the products of fermentation.

The level of fumonisin detected in the ECMR (0.528 ppm) was considerably less than the 30 ppm considered to be the safe upper limit by the "Animal Nutrition Association of Canada (ANAC)". The data nevertheless suggest that mycotoxin contamination is an issue to be taken into consideration when using complete mixed feeds that are rich in protein and moisture, and ensiled over an extended period prior to feeding.

It is suggested that the poorer performance of cttle fed the CMR and ECMR diets may have been related to the known negative effect of the presence of cyanogenic glucosides in the cassava foliage, which was of a “bitter” variety used exclusively for starch production. The addition of the low level (4%) of brewers’ grains to the CMR diets was based on the findings reported by Binh et al (2017) that this was an effective means of counteracting the potential HCN toxicity associated with bitter cassava varieties. However, the cassava foliage (leaves and petioles), used in the CRM diets, was obtained from cassava plants at the end of their growth cycle immediately prior to, or coinciding with, root harvesting, which is done during the dry season. Dry season conditions lead to soil water stress which is known to result in increased concentrations of HCN precursors in the cassava foliage (Tan 1985).

 The results of the present experiment confirm that local "Yellow" cattle can be fattened on the byproduct pulp from cassava-starch factories using urea as source of rumen ammonia and cassava foliage as the main source of bypass protein, derived by recovering the leaves, petioles and fine stems available at the time of root harvest. These findings complement those of Keopaseuth and Preston (2017) using cassava foliage grown specifically as a forage crop to balance the cassava pulp-urea, but with these feeds offered separately. Growth rates (650g/d) were similar to those obtained in the present experiment with the cassava foliage collected at the time of root harvest and used in the .CMR and ECMR systems. In both these cases, brewers' grains were fed in limited amounts of 1 kg/d fresh basis (equivalent to 4% of the  diet DM basis). Choice of either of these two systems of using cassava foliage will depend on the economic feasibility of collecting and preserving cassava foliage (tender stems, leaves and petioles) harvested immediately prior to the root harvest (Photos 2-5), as opposed to growing cassava foliage as a semi-perennial forage, or the purchase of brewers' grains as protein cource.

The final issue concerns the relevance, from a management perspective, of CMR systems compared with offering the feed ingredients separately. CMR systems undoubtedly have advantages in large scale feedlots where feeder wagons enable major savings in costs compared with hand feeding. But at small and medium scales of operation the CMR system may be more, not less, labor-intensive. The moderate degree of contamination with the fungal fumonisin in the ensiled complete mixed ration indicates that ensiling of a complete mixed feed may not be the way to manage high moisture forage-based feeds under humid tropical conditions. Preparing the  CMR immediately before, or some hours prior to, feeding would appear to be a more appropriate system.

Conclusions

• Growth rates of local Yellow cattle were 622 and 608 g/day when a diet of ensiled cassava pulp, supplemented with urea, cassava foliage (leaves and petioles), brewers’ grains and rice straw, was fed as a completely mixed ration in fresh form or after ensiling for 21 days. Live weight gains were 857 g/day when almost all the protein was in the form of brewers’ grains, and the ingredients were not mixed (apart from the urea which was dissolved in the cassava pulp at the time of feeding).
  
  
• It is suggested that excessively high levels of cyanogenic glucosides in the cassava leaves and petioles, which were collected at the end of the dry season from a “bitter” cassava variety at the time of root harvest, may have contributed to the poorer performance of the cattle fed the CMR diets.

Acknowledgements

This research was done by the senior author as part of the requirements for the PhD degree in Animal Production of Hue University of Agriculture and Forestry, Vietnam. The authors acknowledge support for this research from the MEKARN II project “"Improving Livelihood and Food Security of the people in Lower Mekong Basin through Climate Change Mitigation", financed by Sida. The authors are indebted to Mr. Vakili Vongxay, owner of the Natthanasouck farm where the experiment was carried out, for providing access to cattle, feed resources and infrastructure. The Tropical Feed Resources Research and Development Center (TROFEC) of Khon Kaen University is acknowledged for support in collection of rumen samples and VFA analysis. We thank Dr Bundit Tengjaroenkul, Faculty of Veterinary Medicine, Khon Kaen University for analysis of fumonisin in feed samples.

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Received 30 June 2018; Accepted 11 September 2018; Published 1 October 2018

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