The influence of animal feed composition on greenhouse gas emissions from pig manure – A case study on three farms from Lusaka, Chongwe and Choma districts of Zambia

M Kaoma, F D Yamba* and C Mumba**

Department of Agricultural Engineering, School of Engineering, University of Zambia, Box 32379, Lusaka, Zambia.
* Department of Mechanical Engineering, School of Engineering, University of Zambia, Box 32379, Lusaka, Zambia.
** Department of Disease Control, School of Veterinary Medicine, University of Zambia, Box 32379, Lusaka, Zambia.
cmumba@unza.zm   ;   sulemumba@yahoo.com

Abstract

The primary objective of this study was to assess the influence of animal feed composition on greenhouse gas emissions from pig manure on three farms through the use of the Intergovernmental Panel on Climate Change (IPCC) methodology, which measures the digestibility, gross energy and ash content of feed to determine volatile solids content in manure. The farms in this study were purposively sampled based on good farm management and record keeping systems. The data that formed this study was collected over a period of three months (one month on each farm).

The digestibility (DE) values in feed for farms in Lusaka, Chongwe and Choma districts were 48.7%, 55.1% and 50.3% for growing pigs, while those for adults pigs were 63.6%, 69.1% and 66.0%. The gross energy (GE) values in feed for these farms were 22.68MJ/day, 23.23MJ/day and 16.92MJ/day in growing pigs, while that for adult pigs were 37.8MJ/day, 38.72MJ/day and 28.2MJ/day, respectively. The Ash content values in both feed and manure for growing and adult pigs for these farms were 8.14%, 9.37% and 9.64%. The volatile solids (VS) values in manure for the these farms were 0.58 kg dm/day, 0.51 kg dm/day and 0.41 kg dm/day in growing pigs, while that for adult pigs were 0.69, 0.59 and 0.47 kg dm/day, respectively.  These results seem to suggest that feeds with low digestibility, low ash content and high energy contents excrete high amounts of volatile solids which is a function of methane (CH4) emissions from pig manure. One approach for reducing CH4 emissions from pig manure can be by increasing the digestibility of feed by modifying feed using feed additives or supplements. This would result in larger portion of energy in the pig feed being directed towards creation of useful products (pork), rather than CH4 emissions from manure.

Keywords: Greenhouse gas, methane, feed composition, pig manure

Introduction

Pig production in Zambia is estimated to rapidly grow at 8% per annum (Dirk 2010). This is mainly attributed to higher disposable income and increase in human population. Pig production profitability is commonly enhanced by minimizing feed costs and using low-cost feed ingredients that provide the essential nutrients and energy. However, rations are often formulated to exceed nutrient requirements as a safety factor so as not to limit animal performance. This practice can be costly for producers because excess nutrients are not utilized by the pigs, but excreted in manure. This increase in nutrient excretion can increase methane (CH₄) emissions, a key greenhouse gas contributor for agriculture (Carter et al 2012).

CH₄ emissions from pig manure are related to the amount of volatile solids (VS) content in the manure (Werner 1989). CH₄ production from the manure occurs when the VS contained in the manure decomposes in the absence of oxygen. This occurs mostly when manure is managed in liquid form such as in lagoons, holding tanks or slurry pits (Verge et al 2008). Volatile solids are the undigested organic portion of feed contained in manure and it is estimated from feed intake rates and characteristics. The amounts of VS excreted depend on the digestibility (DE %), gross energy (GE) and ash content (ASH%) in feed and is measured using the Intergovernmental Panel on Climate Change (IPCC) methodology for estimating VS using feed data (Dong et al 2006).

The primary objective of this study was to assess the relationship between feed composition and VS excreted in manure which is a function of CH₄ emissions from manure. This study was driven by the lack of research based information on the influence that feed composition has on the CH₄ emissions from manure. It therefore provides the much needed information on reduction of CH₄ emissions from pig manure through improved feed nutrition.

Materials and methods

A cross sectional study design employing quantitative data collection techniques was employed in this study. The study sites included three farms from Lusaka, Chongwe and Choma districts which were conveniently selected.  

Sampling technique and data collection

This study employed the use of purposive sampling technique. Patton (1990) claims that the logic and power of purposive sampling lies in selecting information rich cases for an in-depth study. Information rich cases are those from which one can learn a great deal about issues of central importance to the research. In this study information rich cases were those farms that had good farm management and record keeping systems. Data on feed composition and feed intake rates were collected through the use of direct observation techniques. The feed composition and intake rates were determined by observing the feed compounding processes (mixing of feed ingredients to make animal feed) and the daily amount of feed given to the pigs over a period of one month on each farm. 

Data analysis

The data collected was entered and analysed using excel spreadsheets in Microsoft 2010 software and EvaPig software (version 1.3.0.4).

Determination of volatile solids in manure

The quantity of volatile solids excreted in the manure produced from the study farms was determined for each class of pigs (growing and adult pigs) through the use of equation 1 as recommended by the IPCC:

VS = GE x (1kg.dm / 18.45) x (1-DE% /100) x (1-ASH% /100)...........Eqation 1

Where:
VS = volatile solids excretion in manure (kg dm/animal/day);
GE = gross energy intake of feed in MJ/day;
DE% = the digestibility of the feed in percent;
ASH% = ash content of the feed in percent.
18.45 = is the conversion factor for dietary GE per kg of dry matter (MJ/kg).

Determination of gross energy (GE) in mega joules per day (MJ/day), digestibility (DE %) and ash content (ASH %) for growing and adult pigs

From the feed composition, GE, DE% and ASH % for growing and adult pigs were determined using EvaPig software (version 1.3.0.4). EvaPig is a calculator of energy, amino acid and phosphorus values of ingredients and diets for growing and adult pigs. It includes a database of chemical composition and nutritive values for about 100 reference ingredients, mostly derived from INRA-AFZ tables (Noblet et al 2003). The GE in mega joules per day (MJ/day) was obtained by multiplying feed intake rate by GE in mega joules per kg, obtained from EvaPig calculator.

Results

Feed composition

Table 1 indicates the feed composition from farms No. 1, 2 and 3. 

Feed intake, Gross energy (GE), digestibility (DE %) and ash content (ASH %) in feed

The results for feed intake rate, GE, DE and Ash content in feed for growing and adult pigs from farms No. 1, 2 and 3 were as indicated in Table 2.

Volatile solids (VS) in pig manure from the three farms

The volatile solids (VS) values in pig manure from farm No.1, 2 and 3 were as indicated in Table 3.

Discussion

These results demonstrate that, the feed from farm No. 1 contained the lowest DE % (48.7% in growing pigs and 63.6% in adult pigs), but with the highest amounts of VS in manure (0.58 Kg dm/day in growing pigs and 0.69Kg dm/day in adult pigs). These results therefore suggest that, the lower the DE% of the feed, the higher the VS excretions in the manure. This is because digestibility determines the amount of nutrients in feed that is utilised by the animal (Dammgen et al 2011).

The manure from farm No. 3 in Choma district contained the lowest VS values. This is probably due to the fact that it had the lowest feed intake rate and highest ash content (ASH%). These findings seem to suggest that lower feed intake rate and higher ASH% in feed, results in lower VS excretion rates. ASH % in feed affects VS excretion rates in manure because ash being the inorganic residue in manure reduces the amount of the organic portion of undigested feed in manure from which VS is formed (Suzanne 2010). These findings also indicate that a slight decrease in feed digestibility has a substantial effect (increase) on the VS excretion rates and subsequently on CH₄ emission rates. 

Conclusions

• These results demonstrate that feeds with low digestibility, high energy contents and low ASH% result in high VS excretion rates in the manure.

  
  

• Volatile solids (VS) are a function of CH₄ emissions from manure. Therefore from feed composition the amounts of CH₄ from animal manure can be estimated.

  
  

• One approach for reducing CH₄ emissions from pig manure can be by increasing the digestibility of feed by modifying feed using feed additives or supplements. This will result in larger portion of energy in the pig feed being directed towards creation of useful products (pork), rather than formation of CH₄ emissions from manure.

Acknowledgements

We are grateful to the University of Zambia, Water and Sanitation Association of Zambia and Southern BioPower for financial and logistical support towards this research work. 

References

Carter S, Sutton A and Stenglen R M 2012 Diet and feed management to mitigate airborne emissions. Air Quality Education in Animal Agriculture, pp 10.

Dammgen U, Amon B, Glydenkaerne S, Hutchings N J, Klausing H K, Haenel D H and Rosemann C 2011 Reassessment of the calculation procedure for the volatile solids excretion rates of cattle and pig in the Austrian, Danish and German agricultural emission inventories. Agriculture and Forestry Research. 2 (61), 115-126.

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Noblet J, Bontems V and Tran G 2003 Estimation of energy value of feeds for pigs. Infra production animals. 16 (3), 197-210.

Patton M 1990 Qualitative evaluation and research methods. Newbury Park: Sage publications, pp 244.

Suzanne S N 2010 Food analysis. Fourth edition. New York: Springer, pp 550

Verge X P C, Dyer J A, Desjardins R L and Worth D 2008 Greenhouse gas emissions from the Canadian pork industry. Livestock Science. 121 (2009), 92–101.

Werner U, Stohr U and Hees N 1989 Biogas plants in animal husbandry: A Practical Guide Friedr. Vieweg & Sohn., pp 153.

Received 5 June 2012; Accepted 11 June 2012; Published 1 July 2012

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