Effect of maturity stages of Fig (Ficus sur) fruits on chemical composition, in vitro digestibility and in sacco dry matter degradability

Diriba Diba, Yoseph Mekasha^{1, 3}, Mengistu Urge¹ and Adugna Tolera²

Wollega University, College of Agriculture and Natural Resources, Department of Animal Sciences;
P.O.Box 395, Nekemte, Ethiopia
diriba.diba@yahoo.com   ;   dnazerawi2010@gmail.com
¹ Haramaya University, School of Animal and Range Sciences
P.O.Box 138, Dire Dawa, Ethiopia
² Hawassa University, College of Agriculture, School of Animal and Range Sciences
P.O.Box 05, Hawassa, Ethiopia; Hawassa;
³ International Livestock Research Institute,
P.O.Box 5689, Addis Ababa, Ethiopia

Abstract

The present study was conducted to investigate the effect of fruits maturity stages at harvest on chemical composition, in vitro digestibility and in sacco degradability of Ficus sur fruits (FSF). The treatments involved different maturity stages of Ficus sur fruits . Color, moisture content, and texture were used to distinguish among the fruit maturity stages. Fruits at early, mid, and late stages of maturity were collected from five trees and analyzed.

The proximate composition of the fruits varied only slightly (0 to 3%) with the progress in maturity of the fruits. The exception was the DM content which increased from 45 to 87% with increasing maturity. The condensed tannins were low (<2%) for all the stages of maturity.  In vitro and in sacco measurements indicated that the fruits at all stages of maturity were theoretically only slightly inferior to cereal grains as sources of digestible energy. However, the high washing loss in the in sacco study (38 to 42%) indicates that much of the digestible carbohydrate was in the form of soluble sugars which, depending on the levels used in the diet, could compromise the realizable net energy value of the diet. As in cereal grains, the crude protein content was relatively low (7.07 to 7.33% in DM).

Key words: condensed tannins, net energy value, sugars

Introduction

Inadequate year round feed supply, both in terms of quantity and quality, is the major constraint that threatens livestock production in the tropics. In Ethiopia, the major source of livestock feed is derived from unimproved natural pasture and crop residues. These feed resources contain high fiber and low digestibility (Seyoum et al 2007; Yoseph et al 2002), which does not support optimum livestock production (Adugna 2012, 2007). Besides, the availability of tropical feed resources follows seasonal dynamics of rainfall whereby there is severe feed shortage during the dry spell.  Consequently, the supply of protein and soluble carbohydrates, which are important for the proliferation of rumen micro-organisms from these feed resources, is marginal. Supplementation of low quality feeds with other feed resources which contain better nutrients is an alternative strategy to improve the utilization of low quality feeds and thereby enhance livestock production. Although commercial concentrates are available, they are limited to urban/peri-urban areas and costly for smallholders. Since cereal grains are commonly used as human food it is not only costly but also affects the economic benefits of feeding to animals (Chala et al 2004). It is, therefore, important to search for alternative and cheap non-conventional feed resources that augment the deficiency of low quality feed resources in the tropics.

Ficus sur fruit (FSF) is among the non-conventional feed resources available in tropical areas. It is commonly grown in different parts of Ethiopia and elsewhere in tropics, and widely consumed by all species and classes of livestock. In spite of this, the nutritional value of these feed resources as livestock feed has not yet been evaluated. Characterization and documentation of the available feed resources is part of the national effort underway to update feed resources database of the country (Yoseph et al 2002). Chemical analysis (Cherney 2000) in vitro digestibility method of evaluation (Tilley and Terry 1963) and in sacco DM degradability studies (Niwińska 2009; Ørskov 2000; Ørskov et al 1980) are among the most commonly used methods in feed quality evaluation. The objective of this study was, therefore, to investigate the effects of maturity stages of FSF at harvest on chemical composition, in sacco degradability and in vitro digestibility.

Materials and Methods

Study areas 

 Feed samples were collected from rural areas of Horro district (located at 09º 38’N latitude and 37º 04’E longitude), western Ethiopia while chemical analysis was conducted at Animal Nutrition Laboratory of Haramaya University (located at 9º 26’N latitude and 42º 3’E longitude), eastern Ethiopia. In sacco DM degradability and in vitro DM digestibility were undertaken at Holeta Agricultural Research Center (located at 09°N; 38'E), central Ethiopia.

Treatments and experimental design

Treatments were composed of three stages of maturity of FSF (early, mid and late) and each treatment was replicated 5 times. Since fruits harvested at different stages of maturity were randomly taken from different trees, a completely randomized design (CRD) was used to analyze the data. The color, moisture content, and texture of the fruits were used to distinguish among the fruit maturity stages. Accordingly, orange red, and yellowish red colors with turgid (moisture-full) fruits were categorized as early maturity while brown and slightly brown color types with moderate moisture content and texture were grouped under mid maturity classes, and pale brown and nearly straw colored with least moisture content and rough texture were taken as late maturity stage (Photo 1).

Photo 1. Ficus sur fruits at early, mid and late maturity stages, from left to right, as identified by skin color

Sampling and sample preparation

The ripening process for most Ficus sur fruits is variable. However, it is common that Ficus sur fruits usually ripen from December to April and it takes, on average, about three weeks for the early stage to reach the late stage. Thus, fruits from the three stages (early, mid and late) were collected at the same time from different trees. Before collection, the different maturity classes of the trees were carefully identified based on the characteristics described above. Fruit samples were collected manually by a person having experience in climbing trees from each Ficus sur tree replications and kept separately in a properly labeled clean polyethylene plastic bags.. The fruit samples were immediately taken to the nearby Animal Nutrition laboratory (Wolega University, College of Agriculture, Shambu campus), and dried at 65^oC to constant weight in forced draft oven. The partially dried samples were divided into 2 equal parts. One of the half was ground to pass through 1mm sieve size in Wiley mill for chemical assay and in vitro DM digestibility. The other half was ground to pass through 2mm sieve size for in sacco DM degradability. For chemical analysis all the three fruits maturity stages collected from five trees were separately analyzed.  For in vitro DM digestibility and in sacco DM degradability samples from the five trees were pooled per each maturity stages and analyzed in triplicates at Haramaya University. 

Chemical analyses 

The analysis for each sample was done in duplicate. The DM and ash contents of the feed samples were determined following AOAC (1995). The NDF, ADF, and ADL were determined based on the method described by Van Soest and Robertson (1985). Hemicelluloses and cellulose were calculated as NDF-ADF and ADF-(ADL+ADI ash), respectively. The N content of the samples was determined by the micro-Kjeldahl method and CP was calculated as N X 6.25. The condensed tannins were determined by vanillin-HCl method of Price et al (1978).

In vitro DM digestibility

The in vitro DM digestibility was determined according to Tilley and Terry (1963) two stage technique for in vitro digestion of forage crops, as modified by Van Soest and Robertson (1985) where a second stage (rumen liquor-pepsin digestion) was substituted by neutral detergent extraction to simulate true digestibility.

In Sacco DM degradability

Feed samples were incubated in three rumen fistulated steers (Boran X Holstein Frisian). Before incubation, the experimental animals were fed with concentrate and roughage at maintenance level. Nylon bags of about 41µm pore size were used to incubate the feed samples. About 6g of ground FSF samples of the three maturity stages were sequentially incubated for 4, 8, 16, 24, 48, and 72 hours in the rumen in duplicate. A control sample was prepared in a similar way and kept for determination of 0 hour incubation. At the end of the respective incubation period, all the samples were carefully removed at the same time and rinsed in cold water to remove the adhered mats and reduce continuous action of microbes in the bag. The samples were repeatedly washed until the wash water is clear and put in oven at 65^oC to obtain partial DM of the residue. To determine the contents of water-soluble fraction, two sample bags of each treatment type were soaked in warm tap water (~39^oC) for 24 hours and then passed through the same washing and drying procedures as the incubated treatment bags. Duplicate bags of each sample were similarly dried for determination of DM content of the samples for calculation of DM disappearance.

Statistical analysis

Data on chemical composition, in sacco DM degradability characteristics, and in vitro DM digestibility of Ficus sur fruits were analyzed using the General Linear Model Procedure of SAS (2008). The model used for the analysis was:

Y_ijk = µ + τ_i+ε_(ij)k; where,

µ= overall mean

τ= the i^th (i=1-3) treatment (fruits stages of maturity);

ε_(ij)k= the error term

Mean separation was made using the Tukey honestly significant difference. The degradation curve was plotted using Excel spreadsheet.

The Neway Excel program (Chen 1997) was used for the computation of the in sacco degradability parameters, which were fitted to the exponential equation:
p = a + b (1- e^ct) (Ørskov and McDonald 1979),
where p is DM degradation (%) at time t. Since the washing loss (A) was higher than the estimated rapidly soluble fraction (a), the lag time was estimated by fitting the model p = A for t<to, p=a + b(1-ect) for t>t_o and the degradation characteristics of the forage mixtures were defined as A=washing loss (rapidly soluble fraction); B = (a+b)-A, which is the insoluble but fermentable part; c = the fractional rate constant at which B will be degraded and the lag time (t) =1/cloge[b/(a+b-A)] (Ørskov and Ryle 1990). The effective DM degradability of the forage species was calculated at rumen outflow rate of 0.02 and 0.05 h^-1.

Results and Discussion

Chemical composition

As expected, the DM content of FSF increased as the stage of maturity advanced from early to late stage (Table 1). Harvesting the fruit for conservation at early stage might not be feasible particularly in humid environment where excess moisture cannot be removed quickly through air drying, which results in loss of nutrients mainly through putrefaction. Moreover, the bulky volume of FSF harvested at early stage needs wider space for curing and it will be too laborious compared to harvesting at mid and late stages. Harvesting the fruits at late stage of maturity is also important for easy curing and grinding to use as energy concentrate. The ash constituent of FSF was highest for the late stage of maturity followed by the mid and early stages.  The ADF composition of FSF decreased with progress in maturity stages indicating that more digestible nutrients concentration of the fruits could be achieved at late stages of ripening. The ADL also followed the same trend as that of ADF.

There was no difference in total condensed tannins (CT) among the different maturity stages. Nevertheless, its composition consistently decreased in magnitude with progress in maturity stages. The present finding is in agreement with Gunduz et al (2013) who worked on cherry fruits involving four stages of maturity, Lima et al (2005) on acerola fruits, and Burda et al (1990) on apple fruits. In this study FSF samples drawn from all trees contained less than 2% CT, which is lower than the threshold (8-10%) considered limiting to nutrient utilization (Waghorn et al 1990).  Njidda and Ikhimioya (2012) noted CTs at 3-4% of diet DM may result in nutritional advantages with respect to increased bypass protein availability and bloat suppression in cattle.

In vitro DM digestibility

There were only minor differences in in vitro digestibility with progress in maturity (Table 2), the values being only slightly less than those recorded for cereal grains and higher than for cereal grain byproducts (RU et al 2002; Josefa et al 2002; Seyoum et al 2007; Salabi et al 2010).

In Sacco DM degradability

Washing loss, the insoluble but rumen fermentable fraction and effective degradability increased with advance in the maturity stage (Table 3).  The overall high levels for washing loss, which increased with maturity (38 to 42%), indicates that much of the digestible carbohydrate was in the form of soluble sugars (Tahir et al 2012) which, depending on the levels used in the diet, could compromise the realizable net energy value of the diet (Preston and Leng 1987). The dry matter (DM) degradability of the fruits increased slightly until 48 hours of incubation (Figure 1) for all stages of maturity.

Figure 1: In Sacco degradability of Ficus sur fruits at different maturity stages

Conclusion

• There were only minor changes in composition and apparent digestibility of Ficus sur fruits with increasing maturity.

  
  

• All the analyses indicated that the fruits were apparently only slightly inferior to cereal grans as sources of digestible energy. As in cereal grains, the crude protein content was relatively low (7.07 to 7.33% in DM).

  
  

• The high washing loss in the in sacco study (38 to 42%) indicates that much of the digestible carbohydrate was in the form of soluble sugars which, depending on the levels used, could compromise the realizable net energy value of the diet.

Acknowledgement

The authors are thankful to Holeta Agricultural Research Center, Animal Nutrition research section for allowing use of laboratory for the In Sacco DM degradability and in vitro DM digestibility experiments. We appreciate the help from Mr Kasahun W/Gebrel for storing the fruits until transported to the study areas. We are indebted to Swedish International Development Agency (SIDA) for financing this experiment and Haramaya University for chemical analysis and overall facilitation.

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Received 28 August 2014; Accepted 20 September 2014; Published 3 October 2014

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