Effect of replacing soybean meal with ground cassava (Manihot esculenta Crantz) foliage in the diet of growing rabbits on feed intake and weight gain

Bui Phan Thu Hang^1,2, Nguyen Van Cuong³ and Vo Lam^1,2

¹ Department of Animal Sciences and Veterinary Medicine, An Giang University
² Vietnam National University Ho Chi Minh City, Vietnam
³ An Giang Agricultural Extension Center
bpthang.agu@gmail.com

Abstract

The current experiment was conducted to determine the effects the soybean meal replacement by cassava foliage meal on growth performance of growing rabbits in Mekong Delta of Vietnam. The thirty male weaned crossbred rabbits (New Zealand White x local female), at 8 weeks of age and with initial live weight of 959 ± 67 g (Mean ± SD) were arranged in a completely randomized design with 5 diets and 6 replications (one rabbit per each experiment unit). The protein content of the soybean meal in the control diet was substituted by 25%, 50%, 75% and 100% by cassava foliage meal. The experiment lasted for 8 weeks.

The results indicated that dry matter, organic matter and crude protein intake was no differences in all dietary treatments. The cassava foliage meal impacted positively on growth performance and feed conversion up to 50% level for replacing soybean meal. Therefore, cassava foliage meal can be an alternate unconventional protein source for replacing soybean meal in growing rabbit diets.

Key words: cassava foliage meal, rabbit, replacement, soybean meal

Introduction

Soybean meal is a high-quality protein feed resource, which is commonly used for livestock feeding (Lopes et al 2017; Lu et al 2019; Alfonso-Avila et al 2022). The cost of soybean meal continues to increase, leading to financial pressure on animal producers. It is necessary to decrease the price of livestock feed especially rabbit, which is a pseudoruminant. Many researches on utilisation unconventional feed resources for substitute soybean meal in animal diet (Kholif et al 2016; Selle et al 2020; Garcia-Santos et al 2021; He et al 2022). Cassava ( Manihot esculenta, Crantz) is a source of high protein plant meal that showed good results as an alternative for conventional protein feeds in animal (Fasae et al 2011; Hue et al 2012; Nguyen et al 2012; Régnier et al 2013; Bui Phan Thu Hang et al 2022; Vo Lam et al 2022).

Cassava is widely cultivated in the tropical and sub-tropical countries. Cassava foliage meal contains high level of crude protein about 21-25% (DM basis) (Ravindran 1993; Promkot and Wanapat 2005; Ampapon et al 2016). True protein is 85% of crude protein (Eggum 1970). Cassava leaves are also good sources of calcium, iron, manganses, zinc and magnesium (Ravindran 1993).

Therefore, the aim of this experiment was to investigate the effect of replacing soybean meal with cassava foliage meal in the diet of growing rabbits on feed intake and growth performance.

Materials and methods

Location and experimental design

The experiment was carried out in a private farm in Thoai Son district, Long Xuyen city, An Giang province. Thirty male weaned crossbred rabbits (New Zealand White x local female), at 8 weeks of age and with initial live weight of 959 ± 67 g (Mean ± SD) were housed in individual cages. The rabbits were fed diets composed of homemade concentrate pellet (CP=18%) , in which soybean meal was substituted with ground cassava foliage at 0, 25, 50, 75, or 100% based as protein of soybean meal (Table 2). Water spinach (Ipomoea aquatica) provided ad libitum. The experiment was a complete randomized design with 6 replications and lasted for 8 weeks.

Feeds, animals and management

Cassava foliage (around 50 cm) with leaves, petioles and stems were collected from sweet cassava plants grown in fields around Long Xuyen city. They were then cut with length 2-3 cm and dried in an oven at 55 ⁰C for 12 hours. All ingredients used in the diets were previously ground fine for making pellet.

The weaned New Zealand crossbred rabbits were vaccinated against Hemorrhagic disease, and de-wormed with Ivermectin. Rabbits were fed homemade pellet in feeders (4% live weight) and water spinach forages were hung in bunches above the feed trough. They were given twice a day, with 50% of the daily supply offered at 08.00h and the remainder at 14.00h. Feeds offered and refusals were recorded daily in the morning to identify the feed intake. Weight gain was recorded every week. The diets were adjusted weekly following their body weights. Fresh water was provided ad libitum.

Chemical analysis

Samples of feeds offered and refused were analysed for DM, CP, CF and ash according to AOAC (2005).

Statistical analysis

The data from the experiment were subjected to analysis of variance using the General Linear Model (GLM) procedure of Minitab Software Release version 17 (2013). Sources of variation were treatments and error. Polynomial equations were fitted to the changes for live weight gain and the conversion using the Excel option in Microsoft software.

Results and discussion

Soybean meal and cassava foliage meal composition

The crude protein in cassava foliage (19.1%) meal was lower than in soybean (46.4%) meal, which led to a gradual reduce in the crude protein content in the trial diets with the higher replacement of cassava foliage meal (CFM). However, cassava foliage meal was higher crude fiber content than in soybean meal (Table 1). The crude protein determined in cassava foliage meal were also lower than those found by Ampapon et al (2016) due to different in stage of maturity, cultivars, climate, soil fertility, sampling process and drying procedure (Lutaladio et al 1984; Ravindran and Ravindran 1988; Bamishaiye et al 2011; Stevens et al 2015; Nobosse et al 2017).

Feed intake, live weight gain and feed conversion

The experimental diets had no effect on nutrients (DM, OM and CP) intake ( p>0.05), which shows that the dietary treatment had the similar palatability (Table 3).

The initial weights for rabbits in different diets were no differences (Table 4). However, the replacing soybean meal with CFM had impact on the final body weight and average daily gain (p<0.01). The 50CFM diets had the highest final body weight and daily weight gain as compared to the control group. The daily weight gain was declined when the rabbits were offered more than 50% substitution level of soybean meal with CFM (Table 4, Figure 1). The results showed that the DM feed conversion rate increased with the higher inclusion of CFM (p=0.02). However, there are no effect on DM feed conversion values as substituting soybean meal with CFM up to 75% (Table 4, Figure 2). These results can be cooperated with the lower crude protein content in the 75CFM and 100 CFM diets and was in agreement with Volek et al (2021).

Figure 1. Curvilinear trend in weight gain (g/rabbit/day) as replacing soybean meal with cassava foliage meal in the diet of growing rabbits	Figure 2. Curvilinear trend in DM feed conversion as replacing soybean meal with casava foliage meal in the diet of growing rabbits

Conclusions

• Nutrients consumption are no differences with soybean meal substitution by cassava foliage meal in the experimental diets.
• Substituting soybean meal with by cassava foliage meal up to 50% level can advantage in production performance of rabbits in terms of final body weight and daily weight gain.
• Cassava foliage meal can be an alternate unconventional protein source for replacing soybean meal in growing rabbit diets.

Acknowledgements

The authors are grateful acknowledge for the infrastructure support for this research from a smallholder rabbit farm in Thoai Son district, Long Xuyen city, An Giang province. We also acknowledge group of DH19CN students for their technical assistance.

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