The two-fold impact of animal manure management is caused by the emissions of volatile organic compounds (ammonia, methane and nitrous oxide) into the air and the release of nitrogen into the soil.

In the case of barn animals these environmental aspects concern two different moments of manure management: the collection and storage phase and the final manure disposal phase. However since in the case of pasture-fed cattle it is impossible to collect the manure, the impact depends on the extent to which it is spread across the meadows which is almost impossible to control.

Collection and storage of manure in barns

The first aspect to consider concerns farm management methods, which in the case of deep straw bedding or other absorbent material may result in manure (cattle) or chicken manure (poultry), and slurry manure when livestock is housed on slatted flooring (cows or pigs).

As it is almost solid, cattle and poultry manure are more easily managed than slurry manure. Therefore, it is preferable, since there are various alternatives for the subsequent stages of storage and disposal. Moreover, manure is produced by herds housed on deep straw bedding, which is better for animal welfare.

After collection, manure is stored to ensure that it is treated in the most appropriate times, places and ways possible. There are several types of storage systems, but an important aspect is coverage: especially as slurry manure can be kept in either open or closed tanks that generate very different impacts from an environmental viewpoint. Uncovered tanks release larger amounts of volatile organic compounds that are generated by spontaneous fermentation phenomena, which further lead to the emission of methane gas, CO2 and other substances.

As in the case of enteric fermentation, by following the indications in the IPCC50 Guidelines it is possible to estimate the emissions of the three main substances generated during storage: methane, carbon dioxide and ammonia. There are three possible approaches among which the tabular approach and the experimental approach; the intermediate scenario, Tier 2, is the one used for calculating environmental impact since it is quite accurate when used with known data.

It is possible to make elaborations that enable us to understand the different impacts of the various modes of storage. However, the formulas are more complex than those used for enteric emissions; please refer to the IPCC documents for further details.

The emissions depend on the quantity and type of manure, and especially on how and where it is stored (the geographical area) as climate exerts a strong influence on the biological degradation processes responsible for the emissions.

In order to improve sustainability, the livestock sector should invest in more rational manure management systems and wherever possible opt for solid manure and therefore deep litter farming systems.

In fact, by observing the data in the environmental product declaration published by COOP Italy we can see that nearly half of the manure produced by beef cattle derives from deep litter farming systems.

The Sustainable Meat Project