Gordon King, Animal Science, University of Guelph
Primitive societies first domesticated animals as a convenient means of meeting immediate needs for food clothing and transport. Subsequently, for many thousands of years, livestock remained only one component of a regionally self-sufficient and basically sustainable method to satisfy human demands. Even within our own province, subsistence agriculture persisted until near the end of the nineteenth century. The pattern of family operated mixed farms, loosely organized into self-contained rural communities and providing food for a number of small but growing urban centers, predominated until after the first world war. Subsequently, mechanization and technological innovation produced substantial challenge, transition, change, consolidation and uncertainty. Many surviving farms throughout the more developed countries are now highly specialized, labor efficient, capital intensive and management demanding components of an integrated agri-food industry producing for both a regional and global market. Successful operation of a modern farm demands sound planning and astute decision making throughout all stages of the production sequence. Managers must be competent at problem recognition and solution, using their own abilities or calling on outside "expert" assistance whenever necessary. Unfortunately, many people in the livestock industry posses little understanding of how the system works or appreciate how animals interact with environments. Thus, they compound problems rather than contribute to solutions.
Livestock cannot be separated from their environment and should never be considered in isolation from that environment. Periodic environmental assessments are necessary to determine if the system is making the best use of resources is an ecologically friendly manner while satisfying the needs of the farming family and general society. The accompanying figure illustrates the potential options arising from ignoring environmental factors or from performing an holistic environmental assessment. Unfortunately, personal or political motives and preferences often dictate that something other than the most advantageous option is continued or initiated.
Higher animals posses complex organ systems that respond to appropriate
stimuli and work in concert to perform their essential body functions. Signals
received from the surroundings by the sensory organs may produce a local reflex
action or are processed in the central nervous system. Mild signals produce no
responses but stronger stimuli initiate physiological or behavioral
Adaptation and acclimatization. Animals respond to physical, chemical, climatic and biological stimuli from their surroundings. This external environment, representing all non-genetic factors that influence responses, interacts with the animal's genotype to determine performance. The situation is even more complex in livestock production since human intervention can influence both genotype and the external environment. Under these conditions productivity is dependent on a genetic x environment x management interaction.
All species respond to changing natural environments through altering
phenotype and physiology. Wild animals experience continuously changing
conditions so their survival often depends on the ability to adjust or adapt to
new circumstances. If a particular species finds that existence in a certain
region is threatened through food shortage, inclement weather, excess predators
or other causes it can, if mobile, simply move to a more favorable area and
survive without change in genotype or phenotype. Alternately, new
genotypes arise routinely through the random recombination of genes that occurs
in each passage from one generation to another or, in even rarer instances,
through mutation. If an altered genotype results in a phenotypic change renders
an organism more suited to a particular environment, those possessing the trait
should have a better chance of leaving offspring for the next generation. In
this way characteristics that are beneficial in coping with environmental
change can be introduced and multiplied within populations.
Adaptation by genetic modification is a comparatively lengthy process extending over many generations and is often essential for the long term survival of wild species. Through natural selection a species develops a range of genotypes representing somewhat diverse morphological and physiological phenotypes that allow continued reproduction and survival in the usual environment. Thus, the species is in harmony with the current environment but also possesses the genetic diversity necessary for adaptation to changing conditions. Modern, high producing livestock, however, have been scientifically bred to maximize a few specific phenotypic traits and posses a much narrower genetic base than their wild ancestors. Although they can still adjust as individuals to many short duration changes in their normal environment, human intervention must protect them from extremes.
All living organisms coexist within an environment composed of all the
biotic and abiotic factors surrounding them. These exterior conditions change
continuously so the inhabitants receive, and must often react to, a multitude
of signals transmitted from the environment. This profusion of messages
originating from and defining the conditions relating to the physical,
chemical, thermal and biological sources located in both the near and distant
surroundings, are stimuli. The animal's sensory organs perceives the various
stimuli and forwards them to the central and autonomic nervous systems for
processing. Stimuli of very low amplitude (intensity) are recognized and
classified but subsequently ignored by the regulatory systems, producing no
detectable response. Any stronger stimulus must be processed further, usually
initiating an appropriate response.
Any environmental change that stimulates physiological, metabolic or behavioral adjustments in body functions may be considered a stress. Animals adjust to most stresses by slightly altering physiological functions so internal environment remains within the normal range and routine activities, including reproduction, are not impaired. This process of temporary adjustment is referred to as acclimatization. Bodily changes involved with acclimatization are usually slight and reversible. Once the stress is removed and the original environment restored, the previous functional status returns. Coping with stress may occasionally demand substantial alterations to body function or characteristics. If functional adjustments are not sufficient to maintain homeostasis, the internal environment is disrupted so that essential activities cannot continue in their previously normal ranges. Unnatural or prolonged stress may become distress. Under such conditions individuals or even entire species might suffer severe or even irreversible changes in function, leading to reproductive failure, illness, death and perhaps extinction. Others may acclimatize to the new conditions and survive but often at reduced levels of productivity, while a few might adapt successfully. One of the main challenges in design and operation of any total confinement livestock unit is managing stress so that it does not progress to distress.
Response to Ambient Temperature
Birds and mammals are warm-blooded (endotherms or homeotherms), possessing a thermoregulatory system that maintains a stable body temperature and uniform internal environment (homeostasis) by converting food energy into heat. All metabolic processes generate substantial heat and much of this is retained within the body of homeotherms by insulating layers of fat, feathers or fur. In contrast to the relatively small number of warm-blooded endotherms, there are many, many cold-blooded species (exothermic or poikilotherms) possessing no specialized heat conserving mechanisms. In these species surface areas are usually quite large relative to the volume of heat generating tissue so that metabolic heat dissipates to the surroundings almost as rapidly as it is produced. Poikilotherms exercise minimal control by moving from sun to shade but body and environmental temperature are approximately equal so they can only be fully active within a rather narrow range. Although keeping warm is energetically expensive for homeotherms, especially if they are small, the ability to maintain a stable body temperature allows them to be active over a wide range and in most climates. Thus, as long as ample food is available, homeotherms remain productive even when poikilotherms are dormant.
Maintenance of body temperature in homeotherms. With the exception of those used in aquaculture, almost all domesticated species are homeotherms who must, to remain healthy and productive, regulate their body temperature within a very narrow range. Thus, heat production must equal heat loss or the animal needs to activate a heat generating or dissipating mechanism and expend energy for this. The Thermoneutral Zone is a relatively narrow environmental temperature range in which heat production offsets heat loss completely, without activation of any conservation or removal mechanisms.
The approximate thermal-comfort zones are (°C): mature cattle - 20 to
25; sheep, fleeced - 5 to 24; sheep, shorn 7 to 29; adult pigs 10 to 24;
piglets, newborn 35 to 39; horses -10 to 24.
Confinement of Livestock
Livestock are confined for the convenience of the owners. Good confinement facilities provide conditions that satisfy all biological necessities for individual animals or groups. Whenever practical, operators try to maintain animals just slightly above the lower critical temperature they are comfortable, consume feed readily and produce just enough metabolic heat to maintain the appropriate core body temperature. Some of the requirements for acceptable confinement units are:
Confinement housing has some advantages and somedisadvantages.
Feeding - must provide ample amounts of balanced diet
must have ample feeder space so all can eat without excessive competition
Social - difficult to establish dominance in larger groups
Footing - unless properly formed or bedded, foot and leg problems
uncomfortable animals will not grow efficiently
Aerosols - dust and gasses may affect animals and attendants
Temperature - confinement is moving a bunch of furnaces indoors
- over half of the feed consumed leaves the building as heat or manure
- must be engineered to maintain comfort zone conditions most of the time
- sudden or severe temperature fluctuations most severe for very young or diseased animals
Lighting - controlled lighting is essential to regulate reproductive
activities in poultry
- may also be important in cattle and pigs
- need sufficient intensity so attendants can see to work
Plants respond to changing photoperiod, with some species stimulated to
shift from vegetative growth to flowering by decreasing day length while others
require the opposite condition. Photoperiodism is also a major factor
regulation sexual activity in animals. Both sexes in most wild animals
demonstrate pronounced seasonal patterns. Mating is programmed to occur at a
particular time of the year so that if successful, resulting offspring will be
born during the season when conditions for survival should be optimal. Strains
of domesticated animals have been selected for prolonged breeding seasons over
many generations so dairy cattle, pigs and several poultry species may
reproduce throughout the year. Temperate sheep and goats species are still
short day breeders, only mating in the fall as photoperiod declines so young
will be born the next spring when natural grazing should be improving. Mares,
in contrast, are long day breeders, stimulated to become sexually active as
days lengthen in late spring or early summer with foals born during the
following spring. Under total confinement conditions, artificial lighting
cycles can be used to induce out of season matings and parturitions in seasonal
species. Most intensive poultry units control photoperiod to regulate onset of
The optimum facility for confinement of domesticated animals should provide ample space so that stock remain clean and healthy while maintaining them in the lower range of their comfort zone. At such temperatures, the animals would be comfortable, produce just enough metabolic heat to remain stable without using any energy for dissipation and, provided that adequate amounts of a balanced and palatable diet are provided, feed intake and productivity should be maximized. Practical considerations prevent such luxury on a continuing basis but good units provide near ideal environments most of the time.
Obtain additional information on animal environments from the following links.
Dairy Cows - from the University of Alberta
Pigs - from the National Pork Producers Council