Tackling the future challenges of Organic Animal Husbandry - vTI

! Agriculture and Forestry Research, Special Issue No 362 (Braunschweig, 2012) ISSN 0376-0723
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animal’s rations. Seasonal milking is reflected in the performance and age structure of the herd.
Both organic farms maintain herd health through grazing and high-quality forage based feeds.
Scenario 3 represents a hypothetical farm designed and managed to minimize methane emissions
per unit of milk production. Crossbred cattle are raised annually and are heavily reliant on high quality
forages, but not to the degree present on the two pasture-based farms (Scenarios 1 and 2). Grain
accounts for 14% to 19% of DMI, and concentrates add another 3% to 4%. The greater reliance on
energy-dense feedstuffs supports a higher level of unadjusted milk production – 29.5 kg per day
over lactations averaging 320.4 days. Solid manure is collected and composted, prior to field application,
a management method that minimizes manure-methane emissions.
Scenario 4 captures the performance of a typical, high-production, conventional dairy farm with
Holstein cows, a manure lagoon, and a nutrition program based on feeding a Total Mixed Ration
(TMR) and corn silage year-round. Unadjusted average daily milk production is 34 kg per cow over
lactations lasting 413 days on average. The hormone rbST is administered to sustain relatively high
levels of milk production over extended lactations. Use of rbST is correlated with greater frequency
of embryonic losses and spontaneous abortions, more frequent re-breeding, and higher involuntary
cull and death rates than on the lower-production, pasture-based farms. Conventional dairy’s annual
culling rates run between 30 and 35% and are primarily involuntary (Knapp, 2010).
Pasture-based systems lead to higher quality milk. The study compares Energy Corrected Milk
(ECM) as well as unadjusted milk production. ECM is a measure that adjusts milk production by
accounting for the nutritional quality, based on variable levels of fat and protein in milk. By taking
into account the nutritional value of milk, ECM offers a more objective way to compare the quality
of different production systems, especially when comparing farms milking different breeds of
cattle.
Enteric methane emissions from dairy cattle are projected based on milk production, DMI, forage
amount in the diet, and measures of energy intake. The energy intake method recommended in the
EPA’s most recent national inventory of GHG emissions from agriculture (U.S. EPA, 2007).
Results and Conclusions
Table 2 shows that the organic farms used in the study have lower enteric, manure and total methane
than conventional confinement systems. While the unadjusted emissions per unadjusted kg of
milk are only about 4 g per 100 kg apart between Scenarios 1 and 4, there is over a half a kg per
100 kg difference when using ECM. The results suggest that CH4 emissions can be reduced by
selecting breeds that have greater forage conversion efficiencies, and produce higher quality milk.
While average daily production per cow will be markedly lower, so too will feed inputs and the
wastes generated per cow. More research is needed to improve rumen performance, forage quality
and nutrient balance needed to reduce enteric CH4 emissions.
The model suggests replacing liquid manure systems with grazing and manure composting can cut
manure methane as much as 10-fold. Farms that graze and manage dry manure most of the year can
cut total methane per unit of milk production at least in half. Manure deposited directly on fields by
cows essentially eliminates manure-methane losses. While some pasture-based organic dairies cut
manure methane emissions by 90% compared to emissions with an anaerobic lagoon system, the
average organic dairy likely reduces manure-methane emissions by around 50%.
Management practices to reduce stress, improve cow comfort, and permit natural behavior can result
in better animal health and greater longevity. Reducing the involuntary cull, death and downer
rates has the potential to cut the number of replacement cows needed by about one-half, from 50%
or more, to around 25%. Each replacement animal will emit methane for two years prior first freshening.
Greater longevity reduces CH4 emissions over the life of the animal.
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