Substitution of soya bean meal with Neem (Azadirachta indica) leaf meal as a protein source in the diet of sheep: Effect on voluntary feed intake, digestibility and growth

Adjorlolo L K¹, Obese F Y² and Abdul-Kareem S²

¹ Livestock and Poultry Research Centre, School of Agriculture, University of Ghana
lkadjorlolo@ug.edu.gh
² Department of Animal Science, School of Agriculture, University of Ghana

Abstract

This study determined the effect of replacing soya bean meal (SBM) with Neem leaf meal (NLM) in supplements for sheep on a basal diet of rice straw. The influence of graded levels of NLM inclusion in the supplement on acceptability by sheep was first assessed. On the basis of results of the palatability trial, the supplements were reformulated to limit inclusion of NLM to 40% for the rest of the study. Twenty male Djallonke sheep were randomly assigned to four dietary treatments with five replicates in a completely randomised design experiment. Animals on the control treatment were supplemented with a concentrate containing SBM as the main protein source with no NLM (T1 = 0%NLM). The other treatments had SBM replaced with NLM up to 20% (T2 = 20%NLM), 30% (T3 = 30%NLM) or 40% (T4 = 40%NLM). All animals were offered rice straw ad libitum. After an adjustment of 14 days, feed intake was measured for 12 weeks. Digestibility was measured in vivo during the final two weeks of the feeding trial. Animals were weighed every two weeks during the feeding trial. Compared to the control treatment, dry matter and crude protein intakes were higher (p<0.05) for the 20%NLM and 30% NLM but lower (p< 0.05) for the 40%NLM treatment. Dietary treatment did not affect (p> 0.5) dry matter digestibility but influenced (p< 0.01) NDF digestibility. Average daily gains of sheep were similar across treatments. It was concluded that NLM can replace soya bean meal as a protein source in supplements for sheep fed low quality fodder.

Key words: Djallonké sheep, dry season, nim leaves, rice straw, ruminants, supplement

Introduction

In most parts of the tropics, livestock are fed mainly on low quality fodder including crop residues, especially during the dry season when fresh forage for grazing becomes scarce. These low quality forage materials are often highly lignified and deficient in protein and minerals (IAEA 2006). Draught tolerant tree foliage, which remains available, well into the dry season, provides a relatively low cost option for improving the nutrition of ruminants in low input production systems. By supplying nutrients critical to the survival and proliferation of ruminal microorganisms, tree foliage supplementation improves the utilisation of low quality fodder and enhances animal performance in the dry season.

The Neem tree (Azadirachta indica) is a highly drought-tolerant plant (Gowda and Sastry 2000). During the dry season, the Neem tree is one of the few tree species in the Coastal Savannah of Ghana that remain green. It is one of the commonest naturally growing trees in the savannah areas of Ghana. Neem leaves have high levels of crude protein (between 9 and 20%) and low neutral detergent fiber (Adjorlolo 2016; Fasae et al 2018; El-Zaiat et al 2022) compared with other non-leguminous tree leaves. However, the use of Neem leaves as fodder has not received much attention in West Africa despite its reported palatability to sheep and goats in some Asian countries (Chandrawathani et al 2006; Seresinhe and Marapana 2011). The Neem variety in West Africa, although sometimes selected by grazing ruminants is rarely used as fodder by farmers, probably due to its bitter principles. However, studies on toxicity of Neem leaves showed no toxic effects when fed to goats (Bais et al 2002; Amin et al 2008). Some studies have included Neem leaves in ruminant feed at low levels (4% to 6%) and have reported stimulatory effects on feed utilisation and animal growth (El-Zaiat et al 2022; Taethaisong et al 2023). This study was designed to determine the acceptability threshold of supplements containing graded levels of Neem leaf meal (NLM) and the supplementation effects on Djallonké sheep fed a low quality basal diet.

Materials and methods

Location of Study

The study was conducted at the Livestock and Poultry Research Centre (LIPREC) of the College of Basic and Applied Sciences, University of Ghana. The area lies within the Coastal Savannah zone of Ghana, on latitude 05040’N and longitude 00074 16’W. Rainfall in the Coastal Savannah is bimodal and generally lower than most parts of Ghana, with annual rainfall of between 128 and 1709 mm. The major rainy season spans between April and July and the minor rainy season occurs from September to November.

Feed Preparation

Neem leaves were harvested from trees that grew wildly in the study area. They were shade-dried for about five days, after which the leaves were separated from the twigs. The leaves were ground in a hammer mill with a 1mm screen into a meal. The NLM was mixed with conventional feed ingredients at 0 (control), 200, 400 and 600 g/kg (Table 1) to form the supplements for the acceptability trial. Based on the results of the acceptability trial, the formulations of the supplements were adjusted as in Table 2 for the subsequent trials.

The supplements were formulated to have similar crude protein concentrations.

Acceptability Study

Four male Djallonké sheep weighing about 16.6 ± 1.50 kg were used for this trial. Each animal was penned individually in a well- ventilated shed with free access to fresh water. Each sheep was offered the four supplements (Table 1) in a cafeteria style at 08:00 hours daily and allowed to select for two hours, after which rice straw was offered ad libitum.After 14 days of adjustment to the trial conditions, supplement intakes were recorded for another 14 days.

Feed intake and growth study

Twenty growing Djallonké sheep (12 males and 8 females) with an average initial body weight of 14.6 ± 1.50 kg were penned individually in a well-ventilated shed measuring 1.94m by 1.46m with a concrete floor. The sheep were allotted to four dietary treatments of five animals each. Each treatment had three male and two female sheep. They were offered a basal diet of rice straw ad libitum and given supplements containing NLM (g/kg) at 0 (control; T1), 200 (T2), 300 (T3), or 400 (T4) (Table 2). A daily supplement allowance of 1.3% of each animal’s body weight (approximately 25% of voluntary intake) was offered as single meal at 08:00 hour and rice straw was then offered ad libitum. The sheep had free access to water. Orts of rice straw were weighed each morning before feeding to ascertain daily feed consumption. After an adjustment period of 14 days feed intake was measured daily and animal weights recorded fortnightly for 12 weeks.

Feed intake was calculated as weight of feed offered minus weight of feed left-over.

Average daily gain (ADG) was calculated as:

Feed conversion ratio (FCR) was calculated as:

Digestibility Study

During the final two weeks of the growth trial, total faecal collection was done using faecal bags fitted on each sheep and faeces collected daily for seven days. The faecal samples were bulked for each animal, sampled and oven dried at 60^oC to constant weight for dry matter (DM) determination. The dried faeces were ground for chemical analysis.

Digestibility (%) was calculated as:

Chemical analysis

Feed and faecal samples were ground using a laboratory mill through a 1 mm sieve for chemical analysis. Crude protein and ash were determined using the method of AOAC (1995). Neutral detergent fiber (NDF), acid detergent fiber (ADF) and components of fiber were determined using the method of Van Soest et al (1991).

Statistical analysis

Data from the acceptability, feed intake and growth trial were analysed using the General linear model procedure of SPSS statistical software, Version 20 (IBM SPSS 2011). The least significant difference (LSD) procedure was used to separate significant means.

Results and discussion

Chemical composition of feeds

The chemical composition of Neem leaf meal and the supplements are presented in Table 3 and 4 respectively. The Crude protein concentration of 18.1% in Neem leaves used in the current study is high but falls within the range of 9% to 20.9% reported in the literature (Ogbuewu et al 2011; El-Zaiat et al 2022). The NDF and ADF content for Neem leaves were 49.7% and 30.6% respectively and within the ranges of 27.40 to 55.23% for NDF and 18.87 to 46.30% for ADF in leaves of 15 tropical fodder trees studied by Kumar and Sharma (2003). These suggest the suitability of Neem leaves as a protein source for ruminants on poor quality feed.

Acceptability of supplements

Acceptability of supplements decreased with increasing levels of NLM as shown in differences in preference (p< 0.05) of the supplements by sheep (Table 5). The sheep showed a clear preference for 0%NLM supplements with the 60%NLM being the least preferred. The decrease in acceptability was probably because of the bitter taste of Neem leaves. This was in spite of the reported palatability of Neem leaves to small ruminants (Chandrawathani et al 2006; Seresinhe and Marapana, 2011). The bitter taste of Neem leaves, which is attributed to the presence of triterpenoids, especially azadirachtin (Nanang et al 1997) may be tolerated by ruminants after a period of feeding as ruminants are known to detoxify secondary compounds in plants in an allelochemical type of reaction in their system (Lu 1988). This may explain why Neem leaves are reported to be palatable to ruminants in areas where it is a normal part of their diet. Also, there may be varietal difference in palatability of Neem leaves as is the case for nutrient concentrations.

Effect of NLM-based supplements on voluntary feed intake by sheep

With increasing level of NLM in the supplements, dry matter intake increased (p< 0.05) up to 30%NLM. However, with 40%NLM supplement, intake decreased below the control (Table 6). Crude protein intake followed a similar pattern.

The higher dry matter intakes of sheep on 20% and 30% NLM supplements compared to the control could be due to stimulatory effects of NLM on rumen function leading to increased clearance rate and higher voluntary intake. This is contrary to the report by Paengkoum (2010) that inclusion of 12% Neem leaves in the diet of goats had no effect on feed intake. The depression in dry matter intake in sheep on 40% NLM supplement suggests a possible anti-nutritional effect at higher levels of intake of Neem leaves. Although some anti-nutritional factors have been reported in Neem leaves (Adjorlolo et al 2016) their effects on feed intake is still not clear. The higher crude protein intakes in 20% and 30% NLM treatments may be due the increased dry matter intakes which offset the decline in crude protein concentration of the supplements with NLM inclusion.

Digestibility of nutrients by Djallonké sheep

The digestibility of dry matter and its components in sheep supplemented with NLM are shown in Table 7. Dry matter digestibility was not affected (p> 0.05) by the level NLM in the supplement. The crude protein digestibility for the control and the 20%NLM supplement were similar (p>0.05) but higher (p< 0.05) than for 30% and 40% NLM treatments. Digestibility of NDF was higher (p< 0.05) with 20% and 30% NLM supplement than the control but at 40% NLM, NDF digestibility was similar to that of the control.

The observed improvement in NDF digestibility resulting from 20% and 30% inclusion in the supplements suggests an improvement in the activities of fiber degrading microorganisms in the rumen. According to Kharwar et al (2020), Neem leaves contain over 200 bioactive compounds, some of which act synergistically to improve digestion and liver function (Tufail et al 2025). Some of these compounds such as azadirachtin have anti-nutritional properties and may have limited the intake of the 40% NLM supplement. This may explain the observed lower dry crude protein intake (Table 6) and lower NDF digestibility.

Improvement in proliferation of cellulolytic microbes in the rumen usually manifests in improved cell wall degradation in the rumen. The improvement in NDF digestibility with 20%NLM and 30%NLM supplements could be attributed to the NLM having improved the rumen cellulolytic activity better than soya bean meal. However, in a study by Patra et al (2002) there was no difference in NDF digestibility observed when 50% of soy bean meal was replaced with a leaf mixture of Leucaena leucocephala, Morus albaand Azadirachta indica as supplement in sheep on wheat straw as basal diet.

Weight gain and feed conversion efficiency

Dietary treatments did not affect (p> 0.05) average daily weight gains. Also feed conversion efficiency (FCE) was not affected (p> 0.05) by dietary treatments (Table 8).

Similarity in average daily weight gains in sheep across treatments suggests that overall, partial or complete replacement of soya bean meal with NLM in dietary supplements for sheep did not lead to decline in the quality of nutrition of the sheep. It appears the improvements in dry matter and crude protein intakes were offset by declines in crude protein digestibility. The weight gains in this study are higher than the values of 17.8 to 23.7g/d reported for the same breed of sheep fed rice straw supplemented with stylozanthes (Attoh-Kotoku 2011). Feed conversion efficiency was also not influenced by dietary treatments but the values in the present study are superior to what was reported by Attoh-Kotoku (2011) for the same breed of sheep under similar climatic conditions.

Conclusion

Neem leaf meal can partially or totally replace soya bean meal as a protein source in supplements for sheep fed low quality fodder. However, due to its low palatability, NLM inclusion may not exceed 30% of the supplement.

Conflict of interest

The authors have no conflict of interest whatsoever to declare as this work is the result of a purely academic research.

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