**1. Introduction**

Intensive animal farming [1, 2] or livestock farming is an intensive agriculture type that is destined to increase animal production by providing them all necessities and a favorable environment while reducing the rearing cost [3]. The environment provided to the animals here includes nutrition, shelter, water, optimum temperature and humidity, and veterinary management. It is also known as factory farming [4].

The term Factory farming means "any globally adopted farming system where flock of animals are kept under one roof in a confined setting, that is, a cage or stall" [5]. According to the United States Department of Agriculture (USDA), "a farm with 1000 cattle or 125,000 chickens is referred as factory farming system" [6]. However, according to the European Union (EU), "farm carrying 40,000 chickens is referred to as factory farm or macro-farm" [7]. The products of the animal farming industry

are milk, meat, egg, and other animal products which are readily available for human consumption and are much-liked food amongst people across the globe. Feeding the entire world is the sustainable development challenge in the coming few years. Meat plays a major role in this. The demand for meat has increased rapidly over the past 50 years and it has tripled now [8]. According to the estimates of Food and Agriculture Organization of the United Nations (FAO), approximately 68.1 billion animals were slaughtered in 2012 for meat [9]. However, this figure increased to 80 billion in 2018. Poultry meat is the most popular meat worldwide [8].

Based on the above estimates, every individual on Earth is provided with an average of 42.9 kg of meat. In developed nations, average 76.2 kg of meat is consumed by individuals and, on the contrary, in developing nations, 33.4 kg of meat is consumed by individual on average basis [10]. Asia (42.1%) is the largest producer of livestock followed by America (31.4%), Europe (19.0%) [11], and Africa (5.5%). Besides meat, animals also provided us with milk (5.7 billion tons) and eggs (72 million tons) [11]. Chicken laid 1.25 billion eggs; other poultry laid about 87 million eggs. Much of the animals' products discussed above came from those animals who were raised by someone else on our behalf and amongst them, the majority were reared using intensive animal farming [11]. Factory, intensive, industrial animal farming, and concentrated animal feeding operation (CAFO) all are used for a modern form of intensively rearing of fowl, fish for their various edible products, including their meat (i.e., flesh and fat) and other forms of animal protein (i.e., dairy and eggs). Intensive farming can also be defined as an economic pursuit involving domestic animals for human uses such as obtaining honey, fur, leather, wool, and fertilizer. The sole purpose of this type of farming is to ensure maximum production with maximum profit [12]. According to Archambeaud [13], intensive farming is a farming type where agricultural machinery is employed for achieving higher productivity, that is, the excessive usage of pesticides, fertilizer, or disease or weed-resistant chemicals. This high productivity yield also renders a negative impact on the environment and biodiversity [13] which will be discussed later in this chapter.
