Characterization of vegetables and fruits potential as ruminant feed by in vitro gas production technique

C Tobias Marino, B Hector *, P H Mazza Rodrigues**, L M Oliveira Borgatti**, P Marques Meyer***, E J Alves da Silva** and E R Ørskov*

Department of Agriculture, Hilton Campus, Block M, Hilton Place, University of Aberdeen, Aberdeen, AB24 4FA, UK
caroltobias@hotmail.com
* Macaulay Institute, Craigiebuckler, Aberdeen, AB15 8QH, UK
** Department of Animal Nutrition and Production, FMVZ/USP, Av. Duque de Caxias Norte, 225, Postcode: 13630-000, Pirassununga, Brazil
*** Brazilian Institute of Geography and Statistics – IBGE, Pirassununga, Brazil

Abstract

The potential of several vegetables and fruits wastes, that had expired the date of display in supermarkets shelves, were evaluated as a ruminant feed source through the in vitro gas production technique. Samples were analysed for chemical composition, in vitro gas production and energetic value estimative.

In general, feed analysed showed low dry matter (DM) and Neutral detergent fibre (NDF) content. Crude protein (CP) content was higher for vegetables with exception of carrot and turnip, compared to fruits. Total values of in vitro gas production were highest for orange, followed by onion, squash and clementine and lowest for tomato, grape and blackberry. Similarly, estimated values of metabolizable energy were highest for orange, followed by pea, squash, onion, cabbage, cauliflower and turnip.

Some vegetables and fruits have potential as a ruminant feed according to in vitro gas production technique. However, low dry matter content of these feeds can interfere in the viability of their transport and utilization.   

Key words: By-product, feed evaluation, nutritive value, vegetables wastes

Introduction

Despite all scientific technologies that have been developed and implemented over the past few decades, the world is still searching for better ways to feed livestock and humans in terms of finding new potential feed, as well as, accurate methods of improvement and evaluation of their nutritive value.

Presently, there is an increasing concern related to waste disposal. Until now, landfills are one of the main destinations of all sorts of waste worldwide. They produce a considerable quantity of methane (Raven 2008), a type of gas that has powerful effects on climate change, through the decomposition of biodegradable compounds such as food, green wastes and paper. Less high moisture waste sent to landfills would represent a significant reduction in leachate formation (Blakey 1982), which is responsible for ground-water pollution (Read et al 1997) and also it would be a less attractive place for insects vectors reproduction (Khatib et al 1990).

In this chain of food production and destination for human or animal consumption, ruminants play an essential role due to their capacity to digest the fibre fraction of feed by the rumen microorganisms and efficiently convert by-products that would be disposed in the environment into animal products for human consumption (Grasser et al 1995). So, one option would be to include them in livestock diets, if their relation price/percentage of protein or metabolizable energy was competitive to rest of the traditional products (Martínez Teruel et al 1998).

The main objective of the present study was to investigate the potential of vegetables and fruits that have passed the expiry dates on supermarkets shelves as an animal feed. The analyses were performed by evaluating different feed samples through their chemical composition and in vitro gas production technique.

Materials and methods 

Feed samples

Samples of leftover vegetables and fruits were supplied by J’Sainsbury’s Supermarkets (Aberdeen, UK). They were chosen according to the availability of products wasted during the period of study (3 months). The collection was performed during the morning after the withdrawal of products from shelves due to poor quality or expiry of date of display.

Chemical composition

At the laboratory, all feed samples were removed from plastic or paper packages, chopped without peeling or deseeding, dried at 55°C for a minimum of 36 h. Dry matter (DM), organic matter (OM), crude protein (CP) were determined according to AOAC (1990) and neutral detergent fibre (NDF) determination according to Van Soest et al (1991). In order to cluster the different feed samples for statistic comparisons, they were classified as leafy vegetables: cabbage, spinach, leek, celery and lettuce and as other vegetables: broccoli, cauliflower, turnip, pea, mangetout, onion, squash, tomato, carrot, pepper, mushroom and ginger. At last, the feed samples apple, banana, clementine, orange, grape, melon, pear, plum and blackberry were classified as fruits.

In vitro gas production

The procedure was described by Menke and Steingass (1988). One day prior to the run, 200 mg OM of each sample previously dried and milled was placed in duplicate into numbered 100 mL glass gas syringes (Haberle Labortechnik, Germany). The plungers were greased and placed in a water bath at 39°C. The following morning rumen fluid of two male fistulated sheep was collected and transported to the laboratory. Their diet consisted of hay, pelleted grass and straw. The rumen fluid was strained through gauze and mixed with buffer containing sodium ammonia bicarbonate (35 g NaHCO₃ plus 4 g NH₄HCO₃ per litre) in a ratio of 1:2. Carbon dioxide (CO₂) was provided in a stream in the rumen fluid/buffer mixture throughout the mixing and dispensing procedure. With a semi-automatic pump dispenser 30 mL of rumen fluid/buffer mixture was added to each syringe, all the gas expelled, the volume recorded and placed in the water bath. The volume of the contents was measured after 3, 6, 10, 24, 48, 72 and 96 h. The incubations were made in duplicate of samples in three runs.

Data for gas production were fitted to the following exponential equation: p = a + b (1 – e^-ct), where “p” is the in vitro gas production (mL) at time “t”, “a” is the intercept, which ideally reflects the fermentation of the soluble fraction, “b” is the fermentation of the insoluble fraction, “a+b” is the potential gas production and “c” the fractional rate of gas production (h^-t) (Ørskov and McDonald 1979). The same data were also fitted to an alternative model described by p = b (1 – e^-c(t-L)), where “L” represented the lag time (McDonald 1981). The choice between the principal and the alternative model was based on the fact that the parameters “a” or “L” were statistically different from zero. The principal model was only substituted by the alternative model when the parameter “a” was negative and statistically different from zero or the parameter “L” was positive and statistically different from zero. In order to declare the parameters “a” or “L” statistically different from zero, the confidence interval of 95% was used for these parameters, generated by PROC NLIN from SAS (SAS Institute Inc. 2001). The parameters were declared statistically different from zero when the value zero was not contained inside this confidence interval.

The approximate energy value of the feed samples expressed as metabolizable energy (ME, Mcal/kg DM) was calculated by the expression: ME = 1.24 + (0.1457*GP) + (0.0070*CP) + (0.0224*EE), where GP was the gas produced in mL/200 mg DM in 24 h, CP was the crude protein content and EE the ether extract content of each feed sample, according to Menke and Steingass (1988).

Organic matter digestibility (OMD) of feed samples was estimated by the equation proposed by Menke et al. (1979): OMD (%) = 14.88 + 0.889 GP + 0.45 CP + XA, where GP was the gas produced in mL/200 mg DM in 24 h, CP was the crude protein content and XA was the ash content. 

Results and discussion 

Chemical composition of vegetables and fruits     

Chemical composition of the feed samples used in this study is presented in Table 1 and 2 and expressed on DM basis.

Dry matter content ranged from 4.4 to 18.3% with the lowest value represented by celery and the greatest by pea. Organic matter content was generally high and varied from 71.3% (DM basis) for tomato up to 98.1% for apple. The NDF content was greater for ginger (48.9% DM) and tomato (37.1% DM). Crude protein content ranged from 1.0% DM for apple to 41.4% DM for cauliflower.

Compared to other studies (Gupta et al 1993, Hoelting and Walker 1994 Megías et al 2002), there are differences in chemical composition of the feed samples evaluated in this study and the others. This can be partially explained by several factors that can affect chemical composition of feed, such as stage of growth maturity, species or variety, soil types and growth environment (Chumpawadee et al 2007). 

When samples were grouped in three classes (leafy, other vegetables and fruits), dry matter was higher (P=0.0173) in fruits compared with leafy vegetables without difference from these two groups to other vegetables. Crude protein content was higher (P=0.0048) in leafy and other vegetables compared with fruits. Ether extract content was higher in leafy vegetables (P=0.0383) compared with other vegetables without difference from these two groups to fruits (Table 3).

The average high moisture content of these feeds increases transportation costs and also makes them susceptible to rapid spoilage. Further research may determine practical ways to preserve these feedstuffs. Moreover, it is possible to determine if it is economic viable to use this material as animal feed or as fuel, fertilizer or as a carbohydrate source for microbial fermentation processes (Mirzaei-Aghsaghali and Maheri-Sis 2008).

In vitro gas production, metabolizable energy (ME) and organic matter digestibility (OMD) values

The gas production measured from 3 to 96 h for different feed samples (mL/200 mg OM) and adjusted parameters to exponential equations are presented in Table 4 and 5.

The initial gas produced (3 h) was greater for orange (17.2 mL/200 mg OM) followed by pepper (16.8 mL/200 mg OM). The total gas production when fermentation was complete (96 h) varied from the greatest to orange (74.2 mL/200 mg OM) to the lowest for tomato (25.3 mL/200 mg OM). No differences were observed for in vitro gas production values in different times of measurement when samples were classified in three groups (leafy, other vegetables and fruits) (Table 5).

Megías et al (2002) evaluated some by-products such as pepper, melon, orange and lemon peel and observed greater gas production values when compared to this study.

Gas production parameters are presented in Tables 4 and 5. The intercept “a” ranged from -7.00 to 5.46 where the lowest was observed in carrot and the highest in grape. The values for “b”, which represent the fermentation of the insoluble fraction, were similar in most of the feed samples, except for tomato, grape and blackberry. This can be related with high lignin content of these feed samples that was not evaluated in this study. The fast rates of gas production “c” were observed in pepper, squash, orange and carrot. On the other hand, the slowest rates were observed in plum, tomato and grape. Potential gas production “a+b” was higher in orange, onion, squash, turnip, clementine, apple and pea. It implies that these feed had high availability in the rumen when time was not a limiting factor.

Most feed samples analysed adjusted to the equation p = a + b (1 – e^-ct), with exception of cabbage, celery, broccoli, mushroom and plum, showing necessity of a microbial colonization time (lag time) for their fermentation.

When samples were grouped in three classes (leafy, other vegetables and fruits), fraction “a” was higher in other than leafy vegetables without difference from these two groups to fruits (Table 5).

The ME (Mcal/kg DM) followed the same pattern of potential gas production with the greatest values for orange, pea, squash, onion, cabbage, cauliflower and turnip.

Organic matter digestibility ranged from 37.0 to 84.0 % with the lowest values observed for fruits (grape, pear, plum and apple) and the highest values for melon and celery. Similar results were observed for in vivo organic matter digestibility for cauliflower, cabbage and pea (Wadhwa et al 2006) and for in vitro organic matter digestibility of broccoli (Megías et al 2002). When samples were grouped in three classes (leafy, other vegetables and fruits), OMD was higher (P=0.0219) in leafy vegetables group compared with fruits without difference from these two groups to other vegetables.

Some studies pointed out the potential of by-products from vegetables and fruits processing for ruminants (Nunes et al 2007, Borges et al 2008, Mirzaei-Aghsaghali and Maheri-Sis 2008, Pereira et al 2009). Nutritive evaluation of some vegetable wastes (cabbage leaves, cauliflower leaves and pea pods) showed that they could serve as source of nutrients for ruminants (Wadhwa et al 2006). In an in vitro study, dry matter digestibility of pineapple (61.31%) and passion fruit (62.11%) residue from fruit processing was similar to elephant grass (67.30%) and hydrolysed sugarcane bagasse (64.0%) (Lousada Jr. et al 2006). Lousada Jr. et al (2005) showed that pineapple, passion fruit and melon residue from fruit processing had good nutritive value evaluated by feed intake and apparent digestibility. Similar results were obtained by Correia et al (2006) evaluating pineapple by-product on performance and apparent digestibility in growing goats. Ghoreishi et al (2007) observed that ensiled apple pomace substituted the grain source up to 30% in dairy cows diets without negative effect on milk yield and composition. For other species, Trindade Neto et al (2004) showed that fruits pulp residue could replace corn in piglet’s diets without negative effect on performance.

However, further research is still necessary to gather more information on the viability of these feedstuffs inclusion and to quantify animal response in productive and economic aspects.

Conclusion 

• In this preliminary study, the in vitro gas production technique has shown that vegetables and fruits waste from supermarkets such as orange, onion, squash, turnip, clementine, apple and pea can be explored as a ruminant feed.

  
  

• Further studies are recommended in efficient and practical ways at field conditions to preserve this material. Due to their high moisture content, they are susceptible to spoilage within a few days.

Acknowledgements 

The authors are grateful to J’Sainsburys Supermarkets (Aberdeen, UK) for providing all the samples and its staff for their technical support. Also we thank Macaulay Institute (Aberdeen, UK) and staff for all their assistance.

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Received 20 May 2010; Accepted 30 July 2010; Published 1 September 2010

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