A recent study conducted by Michigan State University provides insight into the greenhouse gas emissions (GHGs) emitted in various U.S. sheep production systems, offering information for livestock producers aiming to reduce their environmental impact.
According to the study, there is considerable interest in reducing GHGs. In the U.S., agriculture accounts for 11% of all GHG emissions. Ruminant livestock emits methane (CH4) via enteric fermentation, contributing about 25% of U.S. CH4 emissions. With approximately 5 million sheep compared to 94 million cattle in the U.S., sheep represent roughly 1% of the cattle industry’s size by mass, a significantly smaller agricultural footprint than countries with large sheep industries like New Zealand and Australia, where sheep contribute 12% and 2% of their GHGs, respectively.
The analysis by Erin B. Recktenwald and Richard A. Ehrhardt and published in Agricultural Systems in May focused on the diversity of production methods within the industry and the differences in carcass sizes due to consumer demand.
Methodology
The research focused on four primary sheep production systems in the U.S., each characterized by varying levels of management intensity and productivity:
• Intensive production: High productivity with animals kept indoors for most of their lives.
• Intensive grazing: High productivity managed on pastures with moderate-to-intensive grazing practices.
• Extensive grazing: Moderate productivity with less intensive pasture management.
• Range: Low productivity grazing on native pastures with minimal input.
These categories were chosen to represent the wide range of sheep farming practices across different regions, taking into account factors like land value, infrastructure, farm size and market focus. The study also included data from feedlots, which finish lambs from range operations as they receive lambs weighing approximately 40-50 kilograms and finish them to heavier weights.
The researchers employed a cradle-to-farm gate life cycle analysis to estimate the GHG emissions from these diverse production systems. Data was collected from 17 sheep operations and four feedlots. The researchers looked at records on reproductive performance, mortality rates and the number of animals sold. These records helped estimate dry matter intake, energy requirements and GHG emissions for each production category.
Key findings
The study revealed substantial variations in GHG emissions among the different production systems. Notably, the more intensive systems, which involve higher inputs and productivity levels, demonstrated lower emissions intensity per unit of lamb live weight. Specifically, emissions ranged from 12.8-20.1 kg of carbon dioxide equivalents (CO2e) per kilogram of lamb live weight, or 10.5-13.3 kg of CO2e per kilogram of sheep live weight.
CH4 from digestion was the main source of GHG in all categories, but its proportion decreased from 79% in the least intensive systems to 46% in the most intensive systems. Breeding ewes were responsible for over 60% of total methane emissions across all categories.
Adding a feedlot stage for lambs in range operations reduced emissions intensity by 25%, resulting in 15.1 kg of CO2e per kilogram of lamb live weight, compared to emissions at the range farm gate.
The study found that the number of lambs weaned per ewe each year was the biggest factor in emissions variation on lamb live weight basis (37%), followed by the ewe replacement rate (27%). On a sheep live weight basis, the age at first breeding accounted for 56% of the variation in emissions.
Mitigation strategies
The study suggests several areas to mitigate GHG emissions in sheep operations, focusing on productivity improvements, feed additives, genetic selection and nutritional management.
One area is improving ewe productivity by increasing the number of lambs weaned per ewe per year. Higher ewe productivity means fewer ewes are needed to produce the same amount of lamb, thereby reducing overall emissions.
Genetic selection also plays a crucial role in reducing emissions. Genetic selection programs have demonstrated that it is possible to breed sheep that emit approximately 20% less methane. Lowering the age at first breeding can reduce emissions before lamb production, but it requires proper nutrition and genetics to ensure successful conception and reproductive outcomes. This strategy is suitable and feasible for more intensive production systems, but it may not be practical for range operations due to resource limitations.
Nutritional management is another important aspect of reducing emissions. Strategic nutritional management, especially around breeding and lambing times, can improve ewe productivity and thus reduce emissions. Providing high-quality feed during critical periods can support larger litter sizes and better lamb growth rates, further enhancing productivity and reducing the overall carbon footprint of sheep operations. The study suggests the use of feed additives such as 3-NOP and seaweed to assist in reducing enteric methane production.
By adopting these strategies, farmers can contribute to mitigating climate change while maintaining efficient and productive sheep farming operations. The study highlights the importance of targeted interventions in high-impact areas, such as ewe productivity, to achieve significant reductions in GHG emissions. — Charles Wallace, WLJ contributing editor
