Dog breeds are specific varieties of dogs that have been intentionally created by humans for particular roles like herding, hunting, and protection. Among all mammals, dogs display the most variety, with more than 360 breeds recognized worldwide. These breeds possess unique physical characteristics such as size, skull structure, tail type, coat texture, body form, and color. Despite this variability, all dogs belong to a single species. In terms of behavior, dogs exhibit a range of qualities, from instinctive behaviors like guarding and herding to personality traits such as sociability, bravery, or even aggression. The vast majority of dog breeds we know today were developed relatively recently, in the last couple of centuries, starting from a limited number of individuals. Their incredible adaptability and our ability to breed them for specific traits have made dogs the most widespread carnivorous species across the globe. Each dog breed reproduces individuals with consistent physical attributes, behaviors, and temperaments, thanks to many years of selective breeding. Kennel clubs and breed registries acknowledge these breeds and issue detailed standards that describe the ideal characteristics of each breed. Terms related to dog breeds vary, covering pure breeds, crossbreeds, mixed breeds, and naturally evolved breeds. Before these breeds were standardized, dogs were identified by their distinct roles and characteristics, with a variety of terminologies used to describe them. However, as society evolved, particularly by the end of the Victorian era, there was a shift from valuing utility to valuing physical appearance. Breeders began to focus on defining and enhancing particular features in their dogs, with the rise of dog shows playing a significant role in shaping the concept of dog breeds as we understand it today. These competitions often highlighted the best specimens within a breed, as defined by their adherence to the breed standard.

Livestock refers to domesticated animals that are bred for a variety of purposes including labor and the production of consumable goods like meat, eggs, milk, and wool. The definition can vary depending on context; sometimes it refers only to animals farmed for food, or more specifically to ruminants such as cattle, sheep, and goats. In some regions, such as the United States, horses are also considered livestock. The U.S. Department of Agriculture (USDA) categorizes meats such as pork, veal, beef, and lamb under livestock, labeling them all as red meat, whereas poultry and fish are not categorized this way. The process of breeding and managing livestock is known as animal husbandry. This practice has been integral to agricultural development throughout human civilizations, evolving greatly over time. While still holding significant economic and cultural importance, the methods of livestock farming have greatly shifted towards intensive animal farming. While this has increased output, it has also raised concerns for animal welfare, environmental sustainability, and public health due to its contribution to greenhouse gas emissions, particularly from cattle, dairy, and sheep farming. The term "livestock" itself emerged in the mid-17th century from the combination of the words "live" and "stock." Historically, "cattle" and "livestock" were sometimes used interchangeably. Today, "cattle" usually means domesticated bovines, while "livestock" encompasses a broader range of animals. Legislation in the United States often defines livestock in specific ways to determine eligibility for agricultural programs; for instance, one act from 1999 legally defines livestock as only including cattle, sheep, and swine for certain reporting requirements.

The practices of animal agriculture across the globe differ greatly, yet they all share a common thread of impacting the environment in many ways. This is particularly true for meat production, which can result in pollution, the release of greenhouse gases, loss of biodiversity, disease propagation, and the extensive use of land, water, and food resources. There are various methods to obtain meat, ranging from organic and free-range farming to more intensive livestock production, as well as subsistence agriculture. The wider livestock sector also encompasses the production of wool, eggs, dairy, the use of animals for plowing, and aquaculture. Among the environmental challenges posed by animal agriculture, greenhouse gas emissions are a significant concern. Ruminant animals like cows and sheep produce methane—a potent greenhouse gas—through the digestive process known as enteric fermentation. Additionally, methane and nitrous oxide released from manure management contribute to the agriculture sector's role in greenhouse gas emissions. To address climate change effectively, especially in the face of an anticipated global population increase by 2.3 billion individuals by 2050, it is crucial to reduce meat consumption substantially. The consumption and production of meat are linked to human demographic trends and economics. As human populations grow and individual incomes or gross domestic product (GDP) rise, meat consumption tends to increase. This raises concerns about the escalating environmental impacts unless there's a shift in current consumption patterns. Predictions suggest that by 2050, global meat consumption might double from the levels in 2000 due to the growing population and higher meat intake per person, particularly in regions undergoing economic development.