This article is a summary of A review of the dairy industry's role in climate change and air quality and the potential of mitigation through improved efficiency by S.E. Place and F.M. Mitloehner, published in Journal of Dairy Science 93:3407-3416, in 2010.
The dairy industry’s climate change air emissions of concern are the greenhouse gases methane and nitrous oxide. With regard to air quality the major emissions from dairy are particulate matter, volatile organic compounds, and ammonia.
The emissions from these compounds can vary depending on a number of factors such as weather conditions, animal type, management, and nutrition.
To be able to compare emission across the diverse operations of the dairy industry, emissions should be reported per unit of output (e.g per kg of 3,5% fat-corrected milk). Improving the dairy industry’s production efficiency (e.g. improvements in management, nutrition, reproduction and cow comfort) is an effective way to reduce emissions per unit of milk.
This report identifies the main areas of concern for the dairy industry with regard to air quality and climate change, followed by a discussion of the importance of mitigation through production efficiency in minimizing dairy’s environmental impact.
The world population is expected to grow from 6.8 billion persons in 2009 to 9.1 billion in 2050 (United Nations, 2009). With no prospects to significantly increase the amount of arable agricultural land, food production must intensify to ensure an affordable abundant food supply. Therefore, emissions mitigation strategies need to balance environmental concerns with the growing global demand for dairy products, along with financial viability to individual dairy producers.
This report focuses on how improving production efficiency reduces emissions per unit of milk.
Production efficiency can be defined as minimizing the amount of inputs (e.g feed, fossil fuels) and outputs (e.g. ammonia and greenhouse gases) to produce a given quantity of milk. Production efficiency improvements can come from minimizing waste, maximizing a dairy cow’s milk production, and maximizing the proportion of her life spent in peak milk production without sacrificing animal health and well-being.
Cows that produce more milk reduce the proportion of total consumed feedstuffs going toward maintenance energy costs. Also, more milk per cow can decrease the total lactating herd size needed to produce a given quantity of milk. Past improvements demonstrate the ability of production efficiency to decrease the environmental impact per unit of milk. Capper et al. (2009) found that historical advances in genetics, nutrition and management of dairy farms reduced emissions by around 50% compared to 60 years ago.
Before calving heifers are consuming inputs and producing both GHG and air pollutants without contributing to the production of milk.
Recent research has found that increasing and altering the nutrients supplied to milk-fed calves can improve growth rates and feed efficiency. Intensified feeding programs for dairy heifers have been shown to lower age at first calving with no reduction, or even an improvement in first-lactation milk yield.
Decreasing average age at first lactation and increasing first lactation milk yield could improve milk’s life-cycle production efficiency and decrease emissions per kilogram of fat-corrected milk, FCM.
Colostrum administration can also affect GHG and air quality emissions per kg of FCM. Failure of passive transfer of immunity through the colostrum leads to increased mortality and morbidity and decreased growth performance. Administering the proper quantity of high quality colostrum within the first few hours of life has been shown to improve long-term animal health and first-lactation performance.
Herd health challenges affect per-unit-of-milk emissions by increasing mortality and losses of saleable milk and decreasing reproductive performance and milk production efficiency. Therefore opportunities exist for the dairy industry to advance production efficiency by improving herd health to simultaneously enhance milk production, reproductive performance and cow longevity.
Environmental or social stressors can decrease the production efficiency. Improving cow cooling during hot weather and grouping animals to minimize behavioral stress has been the focus of research to improve farm profitability, but these improvements have the potential to decrease emissions per kg of FCM as well. Heat stress has been estimated to cost the dairy industry nearly 1 billion USD per year in decreased milk production, reproductive performance and increased death losses. With regard to social stress, grouping the animals according to size and age and avoid overcrowding can improve DMI, consequently improving milk production.
Mastitis: Decreasing the clinical and sub-clinical mastitis rate reduces the GWP (global warming potential) of milk because of increased input-use efficiency, decreased losses of milk production, and a decreased amount of waste milk.
Lameness or injury is a critical herd-health concern, responsible for approximately 20% of mortalities and 16% of selective culling in mature US dairy cows. In addition to decreased survivability, lameness causes decreased milk production and poorer reproductive performance in affected cows. Improved facilities, management, nutrition, and genetics all have the potential to decrease the incidence of lameness and decrease emissions per kilogram of FCM.
Nutrition and feed production
The nutrition of dairy cattle greatly determines the emissions produced directly by the ruminant animal and its waste. Diet composition can alter rumen fermentation to reduce the amount of methane and ammonia produced.
A careful increase of concentrate can led to a decrease in methane emissions, but too much concentrate in the diet can decrease the rumen pH and lead to acidosis. Furthermore, very high concentrate diets diminishes the principal benefit of dairy cows, their ability to convert cellulose, indigestible to humans, into high-quality proteins for human consumption.
Substantial reductions in methane emissions can be achieved without feeding high levels of concentrate by altering nutritional factors like microbial-altering feed additives, dietary lipids, and forage processing and quality.
Forage quality and management can affect both air quality and GHG emissions per kg of FCM. Fermented feeds are a major source of VOC, volatile organic compounds, and require substantial fossil fuel inputs during their production. Therefore, minimizing loss of dry matter throughout the production, storage, and feeding of these feedstuffs will decrease the air quality and climate change impact of each kg of feed. Higher quality forages, produced by ideal crop production, harvesting, and preservation practices, maximize DMI and milk production.
Also forages with higher digestibility and higher rates of passage out of the rumen have the potential to reduce methane emissions for each unit of feed consumed.
Precision feeding, that closely matches the nutrients needed by the dairy cow for maintenance, growth, lactation, and lactation to the supplied dietary nutrients can minimize the environmental impact of the cow’s excreta. Precision feeding requires nutritional models with sufficient accuracy and a level of management that can reduce the feeding system’s variation. By constantly monitoring the dry matter and the nutrient composition of feedstuffs, dairy producers can avoid expensive over-feeding and minimize nutrient excretion that can lead to emissions.
Closely monitoring and ensuring the correct nutrition of individual groups of animals can minimize the risk of other nutritionally influenced diseases and conditions, such as ketosis, lameness, and prolonged anestrous.
Overall, managing feed and feeding programs to minimize waste while maximizing milk production can improve farm profitability and decrease the life-cycle emissions per kg of FCM.
Reproductive performance greatly affects emissions per kg of FCM. Dairy cows that have extended calving intervals because of conception failure spend more time out of peak milk when feed conversion into milk is most efficient. The total productive lifetime of many dairy cows is determined by reproductive performance because reproductive problems is responsible for 26,3% of selective culls in the US.
Restoring reproductive performance in combination with increased milk yield would further reduce emissions per kg FCM.
Reproductive success is influenced by nutrition, genetics, health disorders during transition, management, and the environment.
Sexed semen is a reproductive technology that has the potential to both help and hurt the dairy industry on air quality and climate change per kg FCM. If used selectively, sexed semen can increase the rate of genetic gain in dairy cattle, allowing advantageous traits to become ubiquitous in the entire dairy cattle population. On average, heifer calves tend to be smaller than bull calves, and cause fewer dystocias, and allow for earlier breeding of heifers, fewer mortalities and health problems. However if all animals are bred with sexed semen (or even all heifers), the replacement population for the US dairy herd will increase in size. To keep the population of dairy cattle at a level that does not create an oversupply of milk, the lactating cow cull rate must increase. This can be advantageous, because poor performing animals and those with a poor genetic merit would likely be culled, but in the context of environmental impact per kg of FCM by shortening the total productive lifetime of dairy cows. Furthermore, a larger replacement herd size means more nonproductive emissions for each kg of FCM produced.