Page 55 - The Welfare of Cattle

32 the WeLfare of CattLe

table 5.1 Descriptions of animal type, Body Weight, Manure Production, and recoverable Manure
Body Manure recoverable
Weight Production Manure Manure Manure
kg/day/kg-Body kg/year/500
animal type kg kg/day Weight) kg-Body Weight %
beef (grazing) 634.2 35.1 0.055 10,101 7.8
beef (brood cow) 498.3 27.6 0.055 10,108 80
beef (service bull) 770.1 45.5 0.059 10,783 80
dairy (milking) 588.9 42.1 0.071 13,047 75
hogs and pigs (brood sow) 158.5 4.9 0.031 5,642 75.8
hogs and pigs (market hog) 61.2 4.9 0.080 14,612 75.8
Chicken layers 3.2 0.14 0.044 7,984 92.5
Chicken broilers 3.2 0.18 0.056 10,266 93.3
sheep (ewe) 81.5 2.8 0.034 6,270 33.3
sheep (market lamb) 31.7 1.1 0.035 6,333 33.3
Data source: united states department of agriculture (usda)-natural resources Conservation service (nrCs)
(2016); taylor and ricker (1995).
Note: body weight and daily manure production was extracted from usda-nrCs (2016) and taylor and ricker
(1995), and calculations were made for annual manure estimation.

Today, the animals producing milk, meat, eggs, and important by-products produce more than
a billion tons of animal manure being produced in the USA per year (US EPA, 2013). How manure
is handled on-farm can influence the number and types of microbes found in the manure on-farm
and in the environment.
Table 5.1 shows animal type, body weight, and manure production in various livestock
operations. Confinement operations are able to implement systems to collect and treat manure
while extensive systems allow most of the manure to sit where it was deposited by the animal.
Confinement operations use manure treatment methods such as anaerobic digestion, composting,
and separation of liquid and solid fractions to lower total microbial and pathogen levels prior to
using it as a soil amendment. Extensive systems rely primarily on time, sunlight, and temperature
to reduce microbial levels.
Anaerobic digesters and lagoons used for treatment have a potential to reduce pathogens such as
Escherichia coli and Salmonella. Previous studies showed that 5–6 log reductions of pathogens can
be achieved, when manure is stored in lagoons for about 2–3 months (a 1-log reduction means the
number of bacteria left would be 10% of those that were there before the treatment. A 5-log reduc-
tion would be 10% of 10% of 10% of 10% of 10 of 10%, or a reduction from 100,000 to 1, and a 6-log
reduction would be from 1,000,000 to 1). Similarly, anaerobic digestion experiments showed that
E. coli and Salmonella can be reduced by 5 logs (Pandey et al., 2015; Pandey et al., 2016a). Under
composting environment, when temperature was increased to 55 °C, the E. coli and Salmonella lev-
els were reduced to undetectable levels in less than 5 days (Pandey et al., 2015; Pandey et al., 2016b).
In addition to pathogen inactivation, both anaerobic digestion and composting processes produces
a digestate that is used as soil amendment, and anaerobic digestion produces biogas, a source of
renewable energy (Pandey et al., 2015). In general, animal manure is seen as a valuable commod-
ity, which provides precious recycled nutrients required for improved crop production. This natural
fertilizer reduces the necessity of chemical fertilizers.
Both anaerobic digestion and composting are well-established methods for treating animal
waste and widely used all over the world. The recovery of manure under grazing conditions is rela-
tively low compared to confined systems. For example, approximately 7.8% manure is recovered
from beef operation under grazing conditions, while around 80% manure can be recovered under
confined operations (Table 5.1).