Feed intake, relative preference index, rumen digestion kinetics, nutrient digestibility and live weight change of goats fed selected browse plants

M I Okoruwa

Department of Animal Science, Ambrose Alli University, PMB 14, Ekpoma, Edo – State, Nigeria
okosmich@gmail.com

Abstract

A study was conducted to investigate acceptability, rumen fermentation, digestibility and growth of goats fed selected browse plant supplements. Twenty four growing West African dwarf male goats with mean body weight of 9.00 ± 0.72kg and aged between 9 and 10 months old were used for the study. The diets comprised solely guinea grass and its mixtures with selected browse plants. The experimental diets were; GG₁ (100% guinea grass that served as the control grouped), GS₂ (40% guinea grass and 60% Gliricidia sepium), AO₃ (40% guinea grass and 60% Albina odoratissima) and PA₄ (40% guinea grass and 60% Prosopis africana). The diets were tested for acceptability using the experimental goats to determine mean daily intake, relative preference index and preference ranking. Thereafter, goats were randomly assigned to the four dietary treatments in a completely randomized design with six goats per treatment for rumen, growth and digestibility studies. Results obtained showed that mean daily intake, relative preference index and preference ranking were ranked the same as follows in descending order; PA₄ < GS₂ < AO₃ < GG₁ respectively. Rumen pH, daily feed intake and feed conversion ratio were highest in diet GG₁ while digestibility of crude fibre was highest in diet GS₂ than other diets. Diet PA₄ was highest in rumen ammonia nitrogen, volatile fatty acids, final body weight, total with daily weight gains and digestibility of dry matter, crude protein with nitrogen free extract. Difference did not occur in initial body weight with digestibility of ether extract and ash in goats. It can be concluded that the combination of 40% guinea grass with 60% Prosopis africana and 40% guinea grass with 60% Gliricidia sepium have the potentials to enhance acceptability, rumen fermentation, digestibility and growth of goats.

Keywords: browse plants, acceptability, performance, rumen

Introduction

The inability of livestock farmers to feed their animals adequately throughout the year is a major concern in meeting the future demands of animal protein intake in the tropics. Thus, feeding has been identified as a key factor to the survival and profitability of ruminant livestock in Nigeria (Okoruwa et al 2018). Though grasses are abundant in the tropics, they may not fulfill the nutritional requirement of ruminants particularly during the dry season due to their inherent low nutrient content. In response to this challenge, the usual practice has been to supplement natural pasture with concentrate mixture, but these supplements are often not fed due to their unavailability and escalating cost of their feed ingredients resulting from competition between livestock and man. Thus, one of the cheaper alternatives of enhancing utilization of low quality grasses is by supplementation with high nutritive browse plants. Studies (Oyedele et al 2016; Asaolu et al 2012) have showed that browse plants with high nutritive values can be used as cheap protein supplements which can improve voluntary intake, digestibility and general performance of goats fed low quality feeds.

Gliricidia sepium , Albizia odoratissima and Prosopis africana are such leguminous browse species that can play valuable role in providing supplemented feeds to goats. Ogunbosoye et al (2015) opined that utilization of leguminous browse plants can be potential strategy for increasing the quality and availability of feeds for resource – limited ruminant livestock farmers during the dry season. A researcher (Ogunbosoye and Babayemi 2012) also observed that the foliages of browse plants are medicinal and reservoir of valuable nutrients that are not found in grasses which can be critically important most especially during the off-season. However, most of these browse plants are limited by their low acceptability, high content of toxic compounds and other aromatic compounds which are frequently present in their leaves. Hence, browse plant leaves that may be relished by ruminants require further evaluation to determine their nutritive values. However, possible strategies between combination of pasture and browse plants on preference and nutrient utilization of goats are yet to be exploited for improving their productivity. Thus, this study was therefore designed to assess acceptability, rumen digesta kinetics, digestibility and live weight change of goats fed selected browse plant supplements.

Materials and methods

Experimental site

The study was conducted at the Small Ruminant Unit of the Ambrose Alli University Teaching and Research Farm, Ekpoma in Nigeria, from September to December, 2017.

Experimental diets and animals

Guinea grass was obtained in the pasture land within the Teaching and Research Farm. Gliricidia sepium, Albizia odorotissima and Prosopis africana leaves were cut fresh daily from their naturally growing plants within the University premises and its environs. There were four (4) experimental diets that comprised solely guinea grass and its combination with browse plants. The components of the experimental diets were: GG₁ (100% guinea grass that served as the control group), GS₂ (40% guinea grass + 60% Gliricidia sepium), AO₃ (40% guinea grass + 60% Albizia odoratissima) and PA₄ (40% guinea grass + 60% Proposil africana).

In a completely randomized design, twenty four weaned West African dwarf male goats, aged between 9 and 10 months old with initial mean body weight of 9.00 ± 0.72kg were used for the experiment. The goats were adapted for a period of two weeks to observe their health status.

Preference Study

Following adaptation period, a relative preference study was conducted in a cafeteria feeding approach as described by Larbi et al (1993) using the treatment diets. Goats were confined in separate individual pens of 1.5 x 2.5m. Each pen was provided with a water trough and hanged wooden feed trough at 30cm height designed in a way that each was partitioned into four compartments to accommodate each of the four diets. Approximately 1.00kg each of the diet was weighed and hanged in each of the partitioned wooden feeding trough measuring 50 x 20cm that were strategically placed in the pens daily. The feeding time was between 8:00am and 5:00pm daily for a period of two weeks after the 14days adaptation period. Thus, computed daily intake of the individual diet was used to calculate daily relative preference index (RPI) for each of the test diet offered, in accordance with Larbi et al (1993). This was derived by dividing the daily consumption values by that of the highest consumption values and multiplied by100. Based on these calculations, diets were ranked with the highest consumption value (> 60%) as being the most acceptable, followed by medium (35 – 55%) and low acceptable (< 25%) as reported by Lambart et al (1989) and Obour et al (2015).

Growth and rumen studies

After preference study, animals were randomly allotted to the four treatment diets of six animals per treatment with each treatment replicated thrice of two animals per replicate. The animals were moved into individual pens in an 84day growth study. The diets were offered at 4% of their body weight in dry matter basis twice daily at about 8:00am and 4:00pm. The animals were having free access to water daily throughout the experiment. They were weighed individually at the commencement of the study and subsequently on weekly basis before feeding to determine change in bodyweight.

Rumen study was also preceded by preference study. Rumen liquor samples were taken five hours post feeding directly by means of a vacuum pump with plastic tube thrust into the rumen compartment once weekly from the animals throughout the study. Immediately after collection, pH was measured with Schott CG 840 – pH meter. The samples were then immediately freed of coarse particles by filtration through cheese cloth and centrifuged at 2500g for 20minutes under refrigeration. Rumen ammonia nitrogen was determined using 5ml of the rumen filtrate that was diluted with 45ml of de-ionized water and then 0.5ml of 10ml/L NaOH added. The gas released was measured immediately using gas sensitive electrode. A standard solution was used for the calibration curve for an ammonia electrode. Volatile fatty acids concentration was determined in duplicate using 5ml of the rumen filtrate that was vacuumed distillated. Thereafter, gas chromatography analysis was made, using HP 5880A series gas-chromatograph with hp7671A automatic sampler.

Digestibility Study

Metabolic trial was conducted at the end of the growth and rumen studies to determine the apparent nutrient digestibility. Three goats per treatment were randomly selected and housed separately in individual metabolic cage designed for a complete separation of faeces and urine. The goats were acclimatized for 7days before 7days collection period of feeds and faecal samples. At the end of collection period for each goat, they were separately bulked; mixed properly and about 10% of the sub-samples were pooled and stored in airtight container until they were required for analysis. Thus, apparent nutrient digestibility of the diets was calculated.

Chemical and statistical analyses

Guinea grass, Albizia odoratissima and Prosopis africana, treatment diets and faecal samples were dried in a forced – draught oven at 60⁰C for 48hours, milled and sub-sampled for proximate analysis as described by the procedures of AOAC (1990). Anti-nutritional factors were also determined as outlined in previous publication (Mega 1983; Brunner 1984; AOAC 1990). Rumen ammonia nitrogen and volatile fatty acids concentration were carried out according to the method reported by Cammann (1979) and Zijlstra et al (1977) respectively.

Data generated from the study were subjected to descriptive statistics and analysis of variance (ANOVA) using the general linear modeling procedure (SAS 1985). Significant treatment means were separated using Duncan’s multiple range test (Duncan 1955)

Results

In all the plant species examined, Prosopis africana had highest contents of dry matter, crude fibre and ether extract, while Albizia odoratissima was higher in crude protein than Gliricidia sepium and Prosopis africana (Table1). However, tannin, phytate and oxalate recorded higher contents in Albizia odoratissima than other browse plants (figure 1).

Data on proximate composition of experimental diets are presented in Table 2 (on % DM basis except for dry matter which is on air-day basis). There were no marked differences in dry matter, ether extract and ash between diets analyzed. However, GG₁ had a relatively low crude protein and nitrogen free extract as compared with GS₂, AO₃ and PA₄. Crude fibre was low in GS₂, AO₃ and PA₄ with a remarkable difference from GG₁.

Figure 1. Anti-nutritional factors (%DM) of browse plant species

There were differences in free choice intake in response to diets (Table 3). Mean daily dry matter intake (g) was highest in PA₄ and lowest in GG_1. There were apparent differences in relative preference index (RPI %). It was observed that goats avidly consumed PA₄ immediately the diet was offered than GS₂ and AO₃ and GG₁. However, preference ranking for PA ₄ and GS₂ were grouped into high (>60%), followed by AO₃ (33 – 55%) and before GG₁ (<25%). However, the preference study was in ascending order in this pattern; GG₁ < AO₃ < GS₂ < PA₄ (figure 2).

Figure 2. Mean daily intake and relatilative preference index (RPI) of the treatment diets in ascending order

Results on rumen digesta kinetics and growth parameters are indicated in Table 4. The effect of browse plants on rumen digesta kinetics varied with diets. In the case of rumen pH, it was higher for GG₁ and AO ₃ compared with PA₄ and GS₂. On the other hand, rumen ammonia nitrogen and volatile fatty acids in PA₄ and GS₂ were superior to those in AO₃ and GG₁. Moreover, their trends of ascending order are showed in figure 3.

Data in the present study show that GS₂ and PA₄ resulted in lower intake of diets as compared with AO₃ and GG _1.This lower intake did not significantly affect their weight gains and feed conversion ratios. In line with the data recorded for final body weight, total and daily weight gains and feed efficiency in this study.

Figure 3. Rumen ammonia (NH3) and volatile fatty acids (VFA) of goats in ascending order

Data on apparent nutrient digestibility (%DM) is presented in Table 5. The influence of diets affected dry matter; crude protein and nitrogen free extract digestibility, values recorded in GG₁, GS₂ and AO₃ were lower than the one in PA_4. However, digestibility of crude fiber recorded highest in GS₂ compared with PA₄, AO₃ and GG₁.

Discussion

In general, the proximate composition and anti-nutritional factors data for the three browse plant species in the current experiment fell within the range of values earlier reported by Ogunbosoye et al (2015) and Asaolu et al (2012) respectively. Crude protein values for diets exceeded the ranges of 11.00 to 13.00% crude protein known to be capable of supplying adequate protein for maintenance and moderate growth in goats, with the exception of the protein in control diet which was lower than the reported values of NRC (1981). Variations in nutrient components for diets in this study could be attributed to differences in lignin and proportion of minerals with oil contents that were supplied by the plant species in the diets. Other factors contributing to the differences could be harvesting season and time because leaves develop their structure and morphology according to their age and management. These observations were in accordance with the previous finding of Kouch et al (2003).

Cafeteria technique has been classified as one of the critical means for access acceptability of feeds in ruminants; hence free choice intake of feeds by goats were reported as a predicament in feeding and performance of small ruminants in the tropics (Deng et al 2017). The higher dry matter intake and RPI of goats offered GS₂ and PA₄ were attributed to less toxic factors and high acceptability which influenced the intake of diets positively than GG₁ and AO₃. Previous study (Obour et al 2015) have showed that increase or decrease in dry matter intake and preference could be as a result of voluntary intake, toxin content, nutritional needs of the animals and past experience with the feeds. On the other hand, the lower values observed in GG₁ and AO₃ could probably due to their astringen property and high lignin content in the feeds that deprive the goats of eating. Other factors that could link to this lower acceptability were smell, taste and texture of the diets. This was in accordance with the findings of Larbi et al (1993) who reported that senses enable goats to discriminate among feeds and provide pleasant or unpleasant feelings associated with feeding. Thus, preference ranking of this ascending order GG₁ < AO₃ < GS₂ < PA₄ explained the relative preference index of the diets.

Tannins can react and form complexes by H – bonding with carbohydrates and proteins, but at neutral pH form stronger bonds with proteins. Osakwe and Drochner (2004) noted that complexes with tannin concentration can be deaminated by rumen micro-organism in pH range of 6.5 to 7.0. The lower pH of PA₄ and GS₂ could indicate higher rumen fermentation compared with higher pH of GG₁ and AO₃ that would suggest inhibition of fermentation. The superior rumen ammonia nitrogen concentration of PA₄ and GS₂ indicate a positive effect of supplementation with Gliricidia sepium and Prosopis africana than the reduction in AO₃ and GG ₁ that could be attributed to the inhibitory effects of tannins and lignin on degradability of protein by rumen microbes. However, concentration of ammonia nitrogen in rumen fluid for this study were higher than the values reported in other study with sheep fed Hordeum jabatum hay supplemented with Leaucaena leucocephala (Osakwe and Drochner 2004). The inferior volatile fatty acids concentration of diets AO₃ and GG ₁ compared with diets PA₄ and GS₂ would suggest an inhibitory effect of tannins and fibre components on digestibility of cell wall carbohydrates by rumen microbes. This observation is in consistent with the report of Reed et al (1990). The order of rumen fermentation profile of this study is showed in figure 3. However, study diets resulted in positive weight change, but higher changes were observed on diets supplemented with Prosopis africana and Gliricidia sepium than Albizia odoratissima and guinea grass sole diet. Growth rate obtained in this study were much higher than the reported (Asaolu et al 2012) range of 14.88 to 21.43g/day for goats that were fed dried leaves of moringa, gliricidia and leucaena as supplements to a basal diet of cassava peel. The observation could be due to differences in basal components of the diets, voluntary intakes, efficiency of feed utilization and the physiological state of the animals. Notwithstanding, goats on PA₄ and GS₂ were more efficient in converting feed to weight gain than those on GG₁ and AO₃ as indicated by their lower feed conversion ratio (Table 4).

It was apparent in the present study that dietary supplementation of Prosopis africana and Gliricidia sepium resulted in higher digestibility of dry matter than that of Albizia odoratissima and control diet. Differences in the nature of browse plants and conditions of the experiment could be responsible for the divergent results. This finding was in line with Okoruwa et al (2018) who asserted that there are better efficient utilization of feed and production outcomes of some browse and forage mixtures than in solely browse or forage. The lower digestibility of crude fibre and nitrogen free extract of diets supplemented with Albizia odoratissima and solely grass diet could indicate an inhibition of digestive enzymes activity by tannins and fibre that reduced cell wall carbohydrates, hence they were not relatively well degraded in the rumen. The low and similar values obtained in digestibility of ether extract and ash in this study could be attributed to the interactions between ingredient components of diets which adversely affected microbial activity in the rumen. This inference was also supported by the fact in the study of Okoruwa et al (2018) that lower values obtain in digestibility of diets result from its components.

Conclusions

• Results presented in this study showed that combination of guinea grass with these selected browse plants supplements were found beneficial in goat production.
  
  
• The high nutrient content and relatively low content of anti-nutritional factors of these selected browse plants have placed them among useful fodder trees for livestock feeding during the periods of scarcity and severe feed shortages.
  
  
• Mixtures of 40% guinea grass with 60% Prosopis africana (PA₄) and 40% guinea grass with 60% Gliricidia sepium (GS₂) were found to be best in terms of preference, rumen fermentation, digestibility and growth of goats.

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Received 21 February 2019; Accepted 14 March 2019; Published 1 April 2019

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