Growth rate of male Bali cattle (Bos javanicus) fed leucaena and rice straw diets with increasing levels of cassava

Introduction

The beef production industry of West Nusa Tenggara province in Indonesia, is constrained by the availability of high-quality feeds. Consequently, there have been a series of initiatives to promote the planting and use of leucaena (Leucaena leucocephala) for cattle fattening, resulting in its ongoing and widespread establishment (Dahlanuddin et al. 2019). Due to its practical integration and potential for enhancing profits, the majority of farmers currently feed leucaena as the primary or sole component of cattle diets, especially in the wet season (Panjaitan et al. 2014). This practice has been shown to be associated with substantial improvements in average daily gain (ADG), from an average of 0.2 kg/day on grass-based diets to 0.4–0.6 kg/day on leucaena-based diets (Dahlanuddin et al. 2019). Leucaena has high crude protein (CP) content ranging from 15–40% of dry matter (DM) (Dalzell et al. 1998). However, when fed to ruminants in large amounts, excess nitrogen is excreted into the environment. The inclusion of a fermentable energy source to the ration would mitigate this (Harper et al. 2019) and would also extend the use of leucaena available to a smallholder farmer, or allow for a greater stocking rate on a holding.

Cassava (Manihot utilissima) is extensively cultivated throughout Indonesia, with its root tuber primarily utilised for human consumption. The root tuber of cassava is rich in starch content, with a percentage as high as 73.8% (Retnaningrum et al. 2021) and has an ME value of 12.2 MJ/kg DM (Feedipedia 2016). Fresh cassava (leaf, stem and tuber peels) contains hydrogen cyanide (HCN), which can be reduced through processing methods such as sun-drying and ensiling (Rahmi et al. 2008) and still maintain nutritional quality for ruminant diets (Okpako et al. 2008). Therefore cassava has the potential for incorporation into animal rations, provided that it is carefully formulated to meet nutritional requirements, minimise HCN levels and ensure profitability. The current local price fluctuates and when prices are low, it may be economically viable to utilise this resource for cattle fattening. Farmers could also plant their own cassava in their nonirrigated lands or between leucaena rows.

This study aimed to determine the ratio of leucaena to cassava that results in the best cattle growth rate and most efficient feed conversion for gain ratio; and the most cost-effective combinations between leucaena and cassava to fatten Bali bulls.

Materials and methods

This experiment was conducted over a 12-week period (February–May 2018) and included a two-week adaptation period prior to data collection. The experiment was conducted in accordance with the University of Queensland Animal Ethic Committee Approval number SAFS/517/17/INDONESIA.

Growing Bali (Bos javanicus) bulls (n = 30) with an initial liveweight (LW) of 164 ± 1.8 kg (mean ± s.e.) and aged ~18 months were purchased from the local livestock market and transported to the University of Mataram Teaching Farm (8°31′48″S, 116°11′41″E). These bulls were allocated to one of five experimental treatments (Table 1) in a randomised complete block design. The dietary treatments were 20% rice straw + 80% leucaena hay + mineral mix (A), 20% rice straw + 65% leucaena hay + 15% cassava meal and urea + mineral mix (B), 20% rice straw + 50% leucaena hay + 30% cassava meal and urea + mineral mix (C), 20% rice straw + 35% leucaena hay + 45% cassava meal and urea + mineral mix (D), 20% rice straw + 20% leucaena hay + 60% cassava meal and urea + mineral mix (E) and 20% rice straw + 5% leucaena hay + 75% cassava meal and urea + mineral mix (F). Urea was included in the cassava meal at a 2% level in terms of DM. The mineral mix composition was 50% Ca, 25% P, 0.35% Mn, 0.2% I, 0.10% K, 0.15% Cu, 23.05% NaCl, 0.80% Fe, 0.20% Zn and 0.15% Mg and included at a level of 1% of the total diet in DM terms. The nutrient compositions of feed ingredients and the diets are presented in Table 1.

Bulls were held in individual stalls and had access to experimental diets and water provided ad libitum. The stalls were located in an open-sided covered shed ~1.5 × 2 m in size. The stalls are designed to restrict movement of urine and faeces, inhibit an animal’s access to their neighbour’s food and water but allow animals to see each other.

The cassava utilised in this study was sourced from East Java, then subsequently dried and chopped into chips. The drying of the cassava aimed to preserve the feeding ingredient but also reduce HCN levels to a safe feeding level. Rice straw was sourced from the surrounding area of the University of Mataram teaching farm and was chopped to 2–5 cm lengths and sun dried on a tarpaulin floor for 2–3 days. The dried leucaena, sourced from West Sumbawa, consisted of leaves and edible twigs. Rice straw and leucaena hay were confirmed to have a moisture content of a maximum of 15% before storage in a dry place. The leucaena and cassava chips were ground to 2 mm diameter using a hammer mill (Dongfeng FFC45) to enable homogenous mixing to avoid selection by animals. Ground cassava meal was sprayed with urea (at a 2% DM basis) to ensure an adequate supply of rumen degradable N and enable rumen ammonia to be above the minimum requirement level of 50 mg NH₃-N/L for the rumen microbes (Satter and Slyter 1974).

Animals were fed twice daily at approximately the same time each morning (08:00 hours) and afternoon (16:00 hours). Previous day’s residues were collected each morning and the feed offered was approximately the previous day’s intake plus an additional 10% with at least a minimum of 500 g of residues. Every 2 weeks, intake was accurately determined daily over seven consecutive days. The rice straw was offered at a fixed amount of ~0.5% DM of the LW (or about 20% of the diet). Samples of feed and feed residues were taken every day and bulked over the week-long measurement period. At the conclusion of each measurement period, duplicate subsamples of feed and feed residues were oven dried to a constant weight at 65°C. Water intake was also measured every 2 weeks together with feed intake measurement.

Live weight was measured over 12 weeks by weighing the bulls weekly before morning feeding using a calibrated electronic cattle scale (Asttech FD-01 load bar). The average daily gain (ADG) (kg/head.day) of bulls was calculated from the LW at 12 weeks minus initial LW, dividing by time period (12 weeks). In Week 8, a total collection of faeces over seven consecutive days was conducted to determine feed digestibility. Rumen fluid samples were collected in Week 10 at ~3 h after feeding, using a stomach tube equipped with a metal filter to determine rumen ammonia levels (Chaney and Marbach 1962) and volatile fatty acid (VFA) concentrations (Filípek and Dvořák 2009). Feed gain ratio (FGR) was the ratio between the feed intake to ADG (expressed as kg feed DM/kg ADG). Income over feed cost (IOFC) was measured in Indonesian Rupiah (Rp) and obtained from the ADG x value of the ADG (Rp/kg) minus the average daily feed costs of DM intake (Rp/day) as previously reported by Priyanti et al. (2012) and Cowley et al. (2020).

Experimental data were analysed using the general linear model (GLM) procedure of IBM SPSS version 20 at a significance level of 5%. The statistical model used was the analysis of variance (ANOVA): Y_ij = μ + α_i + β_j + ɛ_ij where y_ij represents the observed value of each individual, μ denotes the overall mean, α_i represents the treatment effect, β_j are the block effects (replicates) and ɛ_ij denotes the residual error (variation among replicates for each treatment). The optimum level of cassava was determined using the regression of the second-rank polynomial (Goedhart and Thissen 2009), which was generated using Microsoft Excel version 2019.

Results

Intake, digestibility and rumen parameter results are summarised in Table 2. Average daily gain differed between diets, with a numerical highest value of 0.68 kg/day for Diet D (45% cassava inclusion). The ADG increased quadratically with increasing levels of cassava (Fig. 1). At a 60% cassava level, ADG was lower than the control and further addition of cassava (75%) caused a loss in LW (Table 2). Based on the quadratic equation in Fig. 1 (y = −0.0003x² + 0.0177x + 0.4264; R² = 0.9106), the optimum ADG was achieved at 29.5% cassava inclusion in the diet. Feeding at a level higher than 45% cassava reduced ADG due to reduced feed intake.

Fig. 1.

Average daily gain (ADG, kg/day) response of Bali bulls to level of inclusion (% of diet) of cassava meal with leucaena. Error bars represent standard error.

Although there was an increasing trend for feed intake (expressed as DMI, organic matter intake (OMI), and digestible DM and OM intakes (DDMI and DOMI respectively) (Table 2), to increase with the addition of cassava to a level of 45% (treatment D), values between Treatments A to D were not significantly different. At a higher than 45% cassava inclusion level (treatment E) DMI and OMI were significantly lower than Treatment D (Table 2). When the cassava was supplied at a 75% inclusion level, feed intake (expressed as DMI, OMI, and DDMI and DOMI) was significantly lower than the control (treatment A). Dry matter intake was reduced to16.3 g DM/kg LW in Treatment D.

Intake changes with increasing levels of cassava is further described in Fig. 2. A quadratic equation described the relationship between DOMI and the level of cassava inclusion in the diet as y = −0.0035x² + 0.261x + 10.866 (R² = 0.773), from which an optimum level of DOMI was achieved at the cassava inclusion level of 37%. Feeding high levels of cassava (45% or more) reduced feed intake. Feed digestibility progressively increased with the inclusion of cassava in the diets (Treatments A to E). At the highest cassava inclusion level (Treatment F) the digestibility declined (Table 2).

Fig. 2.

Digestible organic matter intake (DOMI; g/kg LW) of male Bali cattle fed increasing levels of cassava meal in the leucaena based diet. Error bars represent standard error.

The total water intake, provided by consumed drinking water and also taking into account moisture in feeds, remained at constant levels for Treatments A to D. Total water intake then declined to 13.9 kg/day in Treatment E and 7.9 kg/day in Treatment F, which was associated with the reduced feed intake (Table 2). The water to feed intake ratios did not differ significantly with Treatment (Table 2).

The feed for gain (kg DM/kg ADG) was not significantly different between Treatments A to E, however Treatment F could not be calculated due to the LW loss associated with the high cassava-based diets (Table 3). The IOFC declined at 60% cassava inclusion and became negative when the cassava was included at 75% of the diet (Table 3, Fig. 3).

Fig. 3.

Daily income over feed cost (IOFC; Rp 000/head.day) in male Bali cattle fed leucaena-based diets. Error bars represent standard error.

Urea supplementation was provided to ensure rumen ammonia levels were above 50 mg NH₃-NN/L (Satter and Slyter 1974) so as to meet the rumen degradable N requirements of microbes. This was achieved with the rumen ammonia levels ranging from 78.7–105.7 mg N/L (Table 2) and did not significantly differ between diets. The rumen pH ranged from 6.2–6.5 and did not differ significantly between diets (Table 2). The VFA concentration ranged between 52.5 and 77.7 mmol/L for Treatments A, B, C, D and F but was significantly higher in Treatment E (104.8 mmol/L). There were no significant differences in molar % of individual VFA.

Discussion

This research aimed to provide a better understanding of the required level of cassava when feeding a leucaena-based diet that would provide the highest ADG cost-effectively. It is also essential to understand the upper limits of cassava in the diet when devising rations for fattening cattle.

The formulation of cassava meal with leucaena in this animal pen trial saw high ADG in Bali cattle, achieving 0.68 kg/day in Treatment D (45% cassava meal and 35% leucaena hay). The quadratic response curve indicated that the maximum was reached at 29.5% cassava inclusion. The highest ADG was similar to that achieved with the feeding of leucaena ad libitum with 10 g maize grain DM/kg LW.day (Dahlanuddin et al. 2018) but lower than the highest Bali cattle ADG (0.85/kg.day) reported by Mastika (2003) by feeding a complete diet. Similar findings for the optimal cassava level of around 40% cassava product inclusion for maximum ADG were reported in a number of controlled feeding experiments for cassava meal (Ba et al. 2008; Retnaningrum et al. 2021), cassava bagasse (onggok) (Cowley et al. 2021) or cassava peel silage (Kusmartono et al. 2022).

Feeding high amounts of cassava (more than 45% of the diet) did not increase the ADG beyond 0.68 kg/day, with a quadratic response of ADG to the level of inclusion of cassava meal into a leucaena-based diet. Similar quadratic responses were found in other studies using different forms of cassava and different protein sources (Cowley et al. 2021; Retnaningrum et al. 2021; Kusmartono et al. 2022). The ADG sharply declined when cassava meal was included at 60% of the total diet, with animals losing weight at 75% cassava meal inclusion level.). Cowley et al. (2021) similarly found low and negative ADG values in Madura bulls at 70% inclusion of cassava bagasse. Madura are Bos indicus x javanicus cattle and also indigenous to Indonesia.

The productivity of the animal in this experiment was driven by the reduced intake of the cassava at high levels of inclusion. The pattern of ADG was therefore similar to the quadratic response in intake with level of inclusion of cassava meal. The feed intake was 24.2 g/kg LW without cassava, increasing to a peak of 26.5 g/kg LW, but significantly declined to 16.3 g/kg LW at the highest inclusion of cassava which resulted in significant LW loss. There was a similar quadratic response of DOMI to level of cassava inclusion as with ADG (Fig. 2), with DOMI maximised at around 37% inclusion of cassava. A high inclusion of cassava did not markedly reduce DOMI below that of the 80% leucaena diet, so the negative ADG was probably explained by the lower CP intake.

It is not clearly understood why DMI and the associated ADG declined at high levels of cassava inclusion, as similar quantities of soluble carbohydrate can be found in lot fed rations. The cassava meals have a high level of digestible starch of above 69% (Retnaningrum et al. 2021; Fanelli et al. 2023) which has the potential to cause acidosis. To avoid slug feeding and minimise metabolic disorders related to high starch intake, feeding was carefully managed and provided twice daily with roughage (rice straw) presented before the cassava meals. There was no discernible reduction in rumen pH which was maintained within the normal range at times of measurement. Cowley et al. (2021) suggested that an inadequate supply of crude protein may have depressed intake. To ensure rumen degradable N met the requirement of rumen microbes for this high energy supplement in the current experiment, urea was added to the cassava concentrate at a 2% level on a DM basis. Due to the addition of urea and the high levels of protein in leucaena, the rumen ammonia levels for all animals were within the normal range of 50–250 mg N/L (Preston and Leng 1987) with no significant differences between treatments. The dry matter and organic matter digestibility values (DMD and OMD respectively) increased significantly with the inclusion level of cassava meal to a high of 72% DMD in Diet E (60% cassava inclusion). These higher DMD levels with higher levels of cassava inclusion simply reflect the high digestibility of the cassava with its high starch level. The highest (75%) level of cassava inclusion (Treatment F) saw a significant reduction in digestibility (DMD and OMD), possibly caused by rumen dysfunction such as sub-acute acidosis. That could not be determined in the current study, as the single pH monitoring only determines long-term low rumen pH. Sampling the rumen and testing the pH multiple times throughout the day would provide more information on diurnal pH variation with cassava inclusion. The digestibility values in this Treatment F were still higher than the control and low inclusion level treatments; however the lower feed intake associated with Treatment F may have increased the retention time and thus increased digestibility.

The rumen VFA levels of Treatments B, C, D and F were lower (ranging from 52.5–69.2 mmol/L) than the expected normal range (70–120 mmol/L). Treatment E was associated with significantly higher VFA levels (104 mmol/L) compared to other treatments and also had the highest digestibility values. The rumen VFA concentrations were lower than those reported by Retnaningrum et al. (2021) and Hidayat et al. (2023), who provided similar cassava-containing rations. The concentration of VFA does vary widely according to the diet, intake and time that has elapsed since the animal’s last meal (McDonald et al. 1988). In this study, there seems little relationship between intake and rumen VFA concentration; however digestibilities (except for Treatment E) were generally lower than those reported by Retnaningrum et al. (2021). The relative proportions of acetate and propionate were not significantly different between treatments in this experiment, however the butyric proportion was significantly higher when cassava was incorporated in the diet at levels of 30% or higher.

Overall water intake is a function of the water content in the food and that which is imbibed from the water provided. As such, the high water intake of bulls by drinking from buckets in this experiment was a function of the low moisture of the diets. The water intake was high for Treatments A to D, however in the high cassava Treatments (E and F) water intake was significantly reduced, which corresponded to lower DM intake. The water to feed intake ratios were in the range reported by Marsetyo et al. (2012), who fed a variety of diets to Bali cattle. Feeding a ration containing dry ingredients requires additional assurance of adequate water available to the fattening bulls in these feeding systems. Dahlanuddin et al. (2014) advised that at least 20 L/day should be available for Bali bulls.

Generally, the feed cost represents 70% of the costs producing beef and as such, feed for gain and IOFC are important parameters in the assessment of dietary treatments. The feed for gain ratio quantifies the use of feed for LW gain and therefore can also be used as a tool for forward planning of quantities of feed required for a fattening period. In this trial, feed for gain values ranged from 7.68–9.93 kg DM/kg ADG for Treatments A to E and were not significantly different between these treatments. These values are similar to feed for gain ratio ranges of other similar studies fed concentrates in the diet such as in Bali cattle (9.32–11.54) (Hidayat et al. 2023), Ongole crossbred cattle (9.21) (Lestari et al. 2011) and crossbred Limousin bulls (5.44–19.32) (Retnaningrum et al. 2021).

The feed for gain ratio can also be used in the assessment of IOFC. The IOFC is a gross margin concept and can be used to monitor the profitability of diets. The addition of cassava to up to 45% of the diet provides a more favourable IOFC (14.77 to 24.5 Rp000/head.day), even though prices of the diet treatments were higher. As such, in these Bali bull fattening systems, increased smallholder investment into an improved ration leading to higher ADG, has the potential to increase income. The development of a simple least-cost ration system has been shown to be useful in improving IOFC in these village-based systems (Poppi et al. 2021). A least-cost ration system enables a producer to make changes to a ration formulation with fluctuating prices of potential ingredients. For examples, when cassava prices fall there is opportunity to value add and direct this product for use in cattle fattening rations for increased profits. As well as the tuber, cassava byproducts in the form of leaf and peel can also be utilised but, as they all have different nutrient contents, they will need to be formulated into the diets. In addition, inclusion of cassava will enable a limited area of leucaena to carry more bulls, which is an important consideration for overall smallholder profitability. It is important that rations should not be formulated to contain over 60% of cassava in the diet as this reduced IOFC.

In more extensive systems such as the West Nusa Tenggara region in Indonesia, cassava can be planted alongside the alley of the leucaena and this should result in a more profitable and sustainable system. This is a good research opportunity to explore because farmers in the dry areas own more land, which will enable them to plant cassava. Cassava suits the soil type where leucaena is commonly planted, so an alley cropping of cassava and leucaena can be a solution to provide both high protein and high starch feeds for cattle. The use of cassava in cattle feeding can be opportunistic when cassava tuber prices for human consumption are low.

Conclusions

Cassava meal can be successfully and profitably incorporated into the leucaena-based rations of Bali bulls for fattening. Cassava meals increase ADG (to 0.68 kg/day) compared to leucaena only rations, which have a ADG of ~0.4 kg/day. The use of cassava would also increase the ability to use leucaena throughout the year and, if planted in interrow areas, could increase the carrying capacity of a plot of land, potentially leading to greater overall income for smallholders.

The optimum level of inclusion of cassava was 29.5% (based on the quadratic response curve) but there was little difference in ADG up to 45% inclusion. Feeding a high level of cassava meal (more than 45% of diet) as the source of energy to a high protein diet based on leucaena, reduced feed intake, ADG and profitability of Bali bulls. The income over feed cost was best when Diet D (35% leucaena + 45% cassava) was fed. Although cassava is not readily available in the feeding systems of the West Nusa Tenggara region of Indonesia, there is potential to integrate cassava with leucaena in an alley cropping arrangement, which would improve local supply chain issues, promote high ADG of Bali bulls and increase profitability for local farmers.