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 an environmental assessment.
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 changes.
Birds and mammals are warm-blooded (endotherms or homotherms),
possessing a thermoregulatory system that maintains a stable body
temperature and uniform internal environment (homeostasis)
by convertin food energy into heat. All metabolic processes generate
substantial heat and much of this is retained within the body
of homotherms 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 (ectotherms 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 conrol by moving from sun to shade but bodyand
environmental temperature are approximately equal so they can
only be fully active within a rather narrow range. Although keeping
warm is energetically expensive for homotherms, 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, homotherms remain productive
even when poikilotherms are dormant.
Maintenance of body temperature in homotherms. With the exception of those used in aquaculture, almost all domesticated species are homotherms 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.
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.
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.
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:
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 may increase
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 photoperiods, 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 seasonality
with mating 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 egg laying.
