Comparison of rumen liquor from fistulated and slaughtered cattle in determination of in vitro digestibility of ruminant feeds

Charles Mpemba, Germana H Laswai¹ and Abiliza E Kimambo¹

Tanzania Livestock Research Institute (TALIRI), PO BOX 1425 Mtwara.
charlesmpemba@gmail.com
¹ Sokoine University of Agriculture (SUA), Department of Animal, Aquaculture and Range Sciences (DAARS), PO BOX 3004 Morogoro.

Abstract

The study was conducted to compare the rumen liquor from fistulated and slaughtered cattle in determination of in vitro digestibility of the feeds. The in vitro dry matter digestibility (INVDMD) and organic matter digestibility (INVOMD) of the 4 diets were determined by two stage technique of Tilley and Terry (1963). The in vitro technique followed 2 x 4 factorial arrangements in which the 4 diets were incubated in 2 different sources of rumen liquor; that is rumen liquor collected from fistulated and from slaughtered cattle. The rumen liquor from both sources was assessed for pH and concentrations of ammonia nitrogen (NH₃ -N) and total volatile fatty acids (VFAs). The pH value (6.59±0.06) of the rumen liquor from fistulated cattle was not different (P > 0.05) from that of slaughtered cattle (6.53±0.06). Rumen liquor from slaughtered cattle contained higher (P < 0.05) concentration of rumen NH₃ -N (122.74 ± 1.71 versus 111.34 ± 1.71 mg/l) and total VFAs (151.84 ± 7.75 versus 124.04 ± 7.75 mmoles/l) than that from fistulated cattle. The INVDMD (42.6%) and INVOMD (38.8%) obtained using rumen liquor from slaughtered cattle were significantly (P < 0.05) higher than those obtained using rumen liquor from fistulated cattle (INVDMD = 40.0% and INVOMD = 36.2%). From this study it is concluded that, rumen liquor from slaughtered cattle may be used for estimating in vitro digestibility of ruminant feedstuffs.

Keywords: fermentation characteristics, feedstuffs, inoculum

Introduction

Digestibility of the feed is an important measure of the nutritive value of the feed as it provides the amount of nutrients absorbed by the animal. The digestibility is determined accurately by in vivo technique. However, this technique is normally expensive, tedious and time consuming. Due to this numerous attempts have been made to develop simple techniques of determining digestibility of animal feedstuffs. The two stage in vitro technique of Tilley and Terry (1963) is one of such techniques, whereby digestibility of the food is determined by reproducing in the laboratory the reactions that take place in the alimentary tract of the animal (McDonald et al 2010). The technique relies on the rumen liquor which is normally obtained from fistulated ruminants. This practice has challenges due to moral and ethical issues related to animal welfare and management costs of maintaining these animals.

Numerous attempts have been made to search for other sources of rumen liquor. The use of slaughtered cattle as source of rumen liquor for the estimation of the in vitro digestibility of feeds has been proposed by various authors (Borba et al 2001; Mohamed and Chaudhry 2012; Chaudhry 2008; Mutimura et al 2013). The quality of rumen liquor is mostly affected by the diet of the donor animal (Mould et al., 2005). However, the information on the diet of slaughtered cattle and how it can affect the quality of rumen liquor and hence the in vitro digestibility values is lacking. Therefore the objective of this study was to compare rumen liquor from fistulated and slaughtered cattle used as inoculum in in vitro two stage techniques for estimating digestibility of ruminant feeds

Materials and methods

The experiment was conducted in the animal nutrition laboratory of the Department of Animal, Aquaculture and Range Sciences (DAARS) at Sokoine University of Agriculture (SUA) Morogoro Tanzania. The diets were made from Cenchrus ciliaris hay and different levels of concentrates. The formulated concentrate mixture contained 58.5% hominy meal, 39% cotton seed cake, 1.95% mineral mix and 0.5% salt. This concentrate mixture substituted hay at 0, 10, 20 and 30 percent to make diets 1, 2, 3 and 4, respectively (Table 1). Feed samples were ground to pass through a 1 mm sieve; labeled and stored in airtight containers for DM and ash determination.

The rumen content was obtained from the 4 fistulated steers and 4 slaughtered cattle concurrently. Both the solid and liquid contents were collected. Rumen content from fistulated cattle was collected before the morning feeding, and was taken through the fistulae of the steers by hand and poured into a large warmed thermos. Rumen content from the slaughtered cattle was collected from 4 animals which were selected randomly from the herd of cattle brought for slaughter in Morogoro abattoir. Immediately, after slaughter and evisceration, the rumen was opened and the contents were taken from its central part. Both the solid and the liquid contents were collected into large warmed thermos flasks until full leaving no headspaces. The firmly sealed flasks were immediately taken to the laboratory within 1 h from the time of sampling.

At the laboratory, the rumen contents from each animal were measured for pH using a portable pH meter. Then the rumen contents was divided into 2 parts, one part was put into 2 plastic bottles, each containing 250 mL, for determining the rumen NH₃-N and total VFA. Twelve mL of concentrated (6 mol/L) H₂SO₄ was added to the rumen contents to be used for determination of NH₃-N to stabilize the nitrogen. The bottles containing rumen liquor were stored in a deep freezer at -20 °C. The other part of rumen content from each animal was thoroughly mixed separately and thereafter filtered into warm flasks using double layer of cheese cloth while being fluxed with CO₂ gas. The flasks were put in a water bath maintained at 39 °C and bubbled with CO ₂ gas for 5 min to maintain an anaerobic environment.

The in vitro dry matter digestibility (INVDMD) and in vitro organic matter digestibility (INVOMD) of the diets were determined according to the procedure of Tilley and Terry (1963).

Chemical analysis

Dry matter (DM), ash, crude protein (CP), Crude Fiber (CF) and Ether Extract (EE) of the diets were determined according to proximate analysis of the Weende method (A.O.A.C., 2000). The Neutral Detergent Fiber (NDF) and Acid Detergent Fiber (ADF) were determined according to procedures described by Van Soest et al (1991). Samples of rumen liquor were analyzed for concentration of rumen ammonia nitrogen (Rumen NH3-N) and total VFA as described by Abdulrazak and Fujihara (1999).

Data analysis

The data on INVDMD, INVOMD, rumen pH, concentrations of NH₃-N and total VFA were analyzed using the general linear model (GLM) procedure of SAS program (SAS 2003) according to the model:

Y_ij = µ + A_i + E_i

where; Y_ij = value of the j^th INVDMD, INVOMD, rumen pH, NH3-N and total VFA concentrations of rumen liquor from i^th liquor source,

m = the mean effect,

A_i = the effect i^th liquor source,

E_ij = the random error.

Results

Chemical composition of diets

The chemical composition of the diets used in the study from the different institutions is shown in Table 2.

Fermentation characteristics of rumen liquor

Least square means for the rumen pH and concentrations of NH₃-N and total VFAs are shown in Table 3. There was no significant difference (P > 0.05) in the pH of rumen liquor from fistulated and slaughtered cattle. Rumen liquor from slaughtered cattle had significantly higher (P < 0.05) concentrations of NH₃-N and total VFAs than that from fistulated cattle.

Average values for in vitro digestibility of the diets

Table 4 shows the mean values for INVDMD and INVOMD of the diets obtained by in vitro technique of Tilley and Terry (1963), utilising rumen liquor from fistulated and slaughtered cattle. Diet 4 had significantly higher (P < 0.05) values for INVDMD and INVOMD than other diets followed by diets 3 and 2, and least for Diet 1.

Table 5 shows the mean values of INVDMD and INVOMD obtained by in vitro Tilley and Terry (1963) techniques using rumen liquor from fistulated and slaughtered cattle. The values for INVDMD and INVOMD obtained using rumen liquor from slaughtered cattle was significantly (P < 0.05) higher than those obtained using rumen liquor from fistulated cattle.

Discussion

Chemical composition of the feeds

Substitution of hay with concentrate in the diets improved the CP contents of the diets while decreasing the fiber contents of the diets. The chemical composition of the diets used in the present study differed from one another and this was intended to bring variability on the digestibility values. The values of CP in Diets 2 – 4 were higher as compared to Diet 1 because the CP content in the concentrate used to formulate the different diets was higher than that in hay, hence increased the CP values of the diets. It is widely known that supplementation of hay with concentrate increases the nutritive values of the forages (Ramírez et al 2007).

Fermentation characteristics of rumen liquor

The observed pH values for rumen liquor collected from fistulated and slaughter cattle were within the range considered to be optimum for functioning of rumen microbes (McDonald et al 2010; Ndlovu 1992 and Van Soest 1994). The values of pH were within the normal range due to high feed intake and the type of feed which may increase chewing activity and saliva production that act as buffer for pH (Mekasha et al 2003). Since the experiment was carried during the dry season, it is possibly the slaughter cattle were feeding on dry forages, trees and shrubs which stimulate rumination and high saliva production. The fistulated cattle were fed hay and concentrate, which could have increased the rate of salivation and hence buffered the pH.

The observed higher concentration of NH₃-N and total VFA in the rumen liquor from slaughtered cattle than fistulated cattle could be an indication of larger and more active microbial population in slaughter cattle rumen liquor (Tejido et al 2002). However, high rumen NH₃ -N concentration has been attributed to inability of rumen microbes to effectively utilize ammonia for microbial growth in the dead animal and could lead to decreased intensity of fermentation, their concentration in the rumen liquor from slaughtered cattle were within the range reported earlier to be optimum for microbial growth and activity (Chaudhry 2008).

In vitro digestibility values

The INVDMD and INVOMD of the diets increased with increased crude protein level. Diet 1 which had no concentrate and having low CP content had lowest value while Diet 4 had highest value. This is in agreement with other studies that has been done and found that addition of the concentrates to the feed increased the digestibility of the diets (Dung et al 2014). This is due mainly to stimulation of rumen microbial growth by high protein diets, which in turn degrades more diets compared to low protein or non-supplemented diets (Chaudhry 2008).

The observed higher values of INVDMD and INVOMD obtained using rumen liquor from slaughtered cattle than from fistulated cattle, showed that there may be large and active microbial population in the rumen liquor from slaughtered cattle as evidenced by the higher concentrations of total VFA and NH₃-N in the rumen liquor from slaughtered cattle than that from fistulated cattle. The results obtained are consistent with those reported by Borba and Ribeiro (1996) that used the two stage technique to make comparison between rumen liquor from fistulated sheep, slaughtered cattle and sheep faeces suspension. The authors suggested the use of rumen liquor from slaughtered cattle as a valid alternative to the traditional method of using rumen liquor from fistulated ruminants. This finding supports previous work done using rumen liquor from slaughtered cattle for in vitro digestibility determination (Borba et al 2001; Denek et al 2006; Parand and Taghizadeh 2010).

Conclusion

• Rumen liquor from slaughtered cattle could be used as inoculum for estimating the in vitro digestibility of ruminant feeds.
  
  
• This will reduce the need for fistulated cattle hence reduce the cost of management of animals and responding to issues of animal welfare.

Acknowledgement

This study was supported by the Association for Strengthening Agricultural Research in Eastern and Central Africa (ASARECA).

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Received 8 October 2017; Accepted 1 December 2017; Published 1 January 2018

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