Dewey L. Harris

Postnatal Growth and Development

Various aspects of growth are covered in other chapters, but because it is such an important topic, it is discussed more directly here. The characteristic S-shaped growth curve of all biological systems, whether it be an increase in weight gain of a plant or animal or increase in number of yeast cells in a population (Brody 1945) is shown in Fig. 5.1. The term growth, as applied to animal production, is often considered to be synonymous with increase in body weight of the animal from conception to maturity. Brody (1945) has defined growth as “the constructive or assimilatory synthesis of one substance at the expense of another (nutrient) which undergoes dissimilation.” The energetic efficiency of growth as just defined is, therefore, the energy stored in the animal per unit of energy consumed. The pig is especially efficient in growth, in comparison with other farm animals. Detailed discussion of the energetic efficiency of growth in meat-producing animals has been provided by Webster (1980). The complex metabolic and endocrine aspects of tissue and animal growth are exciting areas of animal biology and have been reviewed by Trenkle and Marple (1983>) and in a symposium, Concepts of Animal Growth (American Society of Animal Science, 1988).

The Future of Pork Production

The world pig population continues to increase faster than the human population, which is now about 5.5 billion and expected to reach 7 to 8 billion by the year 2020. One often hears the assertion that because pigs compete directly with humans for some of the available food supplies, the importance of pork in the food supply must decline, both on moral and economic grounds, as the population increases. Science and technology are creating changes—in the pig, as well as in production systems —that may assure continued growth of swine numbers and pork consumption throughout the world in the foreseeable future.

The Pig: Past, Present, and Future

The evolution and domestication of the pig has been described in several books (Towne and Wentworth 1950; Mellen 1952; Briggs 1969; Mason 1969), and the student interested in a detailed account of this fascinating story is referred to them. Recorded domestication appears in Biblical accounts as early as 2000 B.C. Despite some ancient cultural and religious taboos forbidding the consumption of pork, the domestication of the pig as a source of human food has persisted, and the continued increases in numbers of swine throughout the world up to the present time provide evidence of the contribution of the pig to human nutrition through the ages.

Production Systems: Perspective and Components

Some decades ago, “raising pigs” was primarily a subsidiary farm activity that took place in mud lots (Fig. 3.1), with minimal shelter, to utilize garbage and leftover grains to produce meat for the farm family. Pasture production systems (Fig. 3.2) predominated through the 1950s, with more intensive systems starting in the 1960s. From these origins, “pork production” has evolved to be a primary enterprise on many specialized farms to convert processed feedstuffs and breeding stock resources into marketable pork products. This modern production often occurs in insulated, ventilated facilities with automated feed delivery and manure disposal. This requires labor competent to care for the stock and operate the equipment which is supervised by managers (who may be the owners) with considerable expertise. This trend is likely to continue.

Pork as Human Food

Pork, along with other animal products, provides protein of higher nutritive value than that present in most plant proteins and also provides other nutrients not found in adequate amounts in plants. Pork supplies nearly one-half of the meat production from domestic animals in the world and about 40% of the meat (excluding poultry) in the United States. The long-term acceptance of pork as a major food source has been a result of its high nutritive value as well as the variety of processing and cooking methods available for its inclusion in many cultures. Those associated with the swine industry must not lose sight of the fact that the consumer ultimately determines the amount and kind of pork produced. The purpose of this chapter is to characterize pork as to its nutrient composition and other properties that affect its acceptability to humans.

Genetics and Breeding Systems

In Chapter 3, it was stated that the genetic aspects of the production system set both the limits and potential for performance of the system. The breeding stock input into the system introduces potentials for animal performance but these are not usually exceeded (experimental lean growth promotants such as ractopamine and somatotropins do increase lean growth potential above that expressed without their use). In this chapter, we will examine alternative breeding systems to provide that input, tools available to the breeder and producer to improve the potential for that input, and the evolution of genetic improvement tools from the traditional showring-based visual appraisal approach to modern computer-based performance testing and genetic evaluation procedures.

Production Systems: Design and Management

Following the review in Chapters 5 through 9 of the understanding of the biological mechanisms as developed from decades of research concerning swine, we return to the systems view presented in Chapter 3. We will consider the principles of how the modern pork production manager needs to organize the production system. Particular attention will be given to the interactions and interrelationships among the components of the system. These interactions mandate numerous compromises and trade-offs as the manager attempts to ensure that economic efficiency is achieved. That is, for a profitable enterprise, the value of the output products must exceed the costs of the input components by a reasonable amount. Profit is necessary in order for the operation to continue. The task is challenging due to fluctuations in prices paid and received and due to the risks from unplanned occurrences.

Nutrition and Feed Formulation

Feed represents 55–85% of the total cost of commercial swine production, depending mainly on the relative costs of feed, labor, and housing in a particular situation. For this reason, it is highly important that economical as well as nutritionally balanced diets are provided during all phases of the life cycle. The economics of swine feeding are largely dependent on local conditions of feedstuff availability and competition for the same foodstuff for use by either humans or other animals. The pig has a digestive system with limited ability to utilize large quantities of forage so that, like the chicken, it is in direct competition with man for available food supplies. The degree of competition is related to cultural differences in food preferences. For example, wheat and potatoes are not usually fed to swine in the United States as the demand for human consumption holds the price too high, but in many other parts of the world these crops are commonly fed to swine. Similar relationships exist for other crops in other parts of the world.

Reproduction and Lactation

A high reproductive rate is essential in a successful purebred or commercial swine enterprise. A knowledge of the normal anatomy and physiology of the female and male reproductive tract is fundamental to the achievement of a high reproductive rate of swine. In this chapter, the following topics are discussed: anatomy of the female and male reproductive tracts, puberty, the estrous cycle, ovulation, factors affecting ovulation rate and time of estrus, movement and survival of sperm in the female reproductive tract, conception rate, duration of gestation, uterine capacity, parturition, male puberty and sexual behavior, composition of semen, sperm survival and storage, artificial insemination, and potentially important techniques, though presently in limited use, such as embryo transfer, artificial control of the estrous cycle, superovulation, and storage of sperm by freezing. Each of the above subjects is of significance in the total picture of reproduction. Overviews of current knowledge of male and female reproduction in swine are recommended (Dziuk 1977; Dziuk and Bellows 1983; Bazer and First 1983; Amann and Schanbacher 1983; Kirkwood and Aherne 1985; Christenson 1986).