The cost of
animal products depends primarily upon the efficiency of three basic biological functions: 1) reproduction and
viability, 2) female product output and 3) rate and composition of
growth (Dickerson, 1970, 1976, 1990; Harris, 1970). Total costs can be separated into two major categories: 1) for the
producing and reproducing female population and 2) for growing weaned or
hatched progeny to market age or weight. Product output similarly comes either
1) directly from the females - as milk, wool or eggs, or 2) from market value
of progeny - as meat. Overall efficiency is measured by the ratio of total
costs to product output, in economic equivalents, over a given period of time
for the production-marketing system (E).
Average
costs per female-year include those for replacements, R = (cost of a
replacement female less average return per culled or dead female)/(mean number
of years of herd or flock life), plus those of a breeding female (d) for fixed
labour, housing and other (Id), variable maintenance feed (Fmd)
and variable feed above maintenance for production (Fpd). Costs per
female year for each of N progeny (o) from weaning to market include average daily costs for fixed items (Io),
variable maintenance feed (Fmo) and variable above-maintenance
feed for growth (Fpo), all multiplied by days of postweaning
growth (D), plus fixed costs for marketing,
slaughter, vaccines, etc. (So). Yearly output per breeding female includes
units of direct output (e.g., milk, wool or eggs) multiplied by value/unit (Pd
• Vd) plus the product from N
market progeny of Po weight and Vo value/unit weight.
Thus overall efficiency in terms of cost/unit of output value can be
visualized as:
It is sometimes convenient to express output values in terms of
equivalent value units (e.g., as feeder calf weight from both calves and cull cows
marketed, or as market lamb weight from lambs, cull ewes and wool sold). Input
costs are best expressed in monetary units based on quantities and cost per
unit (e.g., Fmd = units of feed for maintenance × cost/unit, plus Fpd units of feed for
milk or egg production × cost/unit,
and similarly for maintenance = Fmo
and gain = Fpo of market progeny). If replacement females are
produced within the herd, R =
(postweaning to breeding cost-income from a culled female divided by mean
cow herd life).
Input/output
efficiency (E, Formula 1) can be calculated for herds or flocks at equilibrium
age composition over a typical period of time (e.g., year). Thus differences in
timing of costs and income are minimal, and consideration of differences in
discounted costs vs income are not important for comparisons among
breeds for a given role in a production system. However, there can be
real differences among breeding systems in the timing of input costs vs output
income (e.g., straightbred vs terminal sire × maternal F1 crossbred
female) that may justify including the discounting of expense and income to the
same point in time for the systems compared.
The
performance information required for evaluating breed and cross differences in
efficiency include both outputs and inputs. Outputs are much more easily and
frequently measured. However, differences in output alone greatly exaggerate
the real differences in efficiency, because increased output also increases
inputs, especially of feed intake.
Among traits
affecting output, the very important ones for meat animals are those controlling N, the number of progeny marketed
per female maintained. Increasing N directly reduces costs per unit of
meat output for replacements (R) and for breeding female maintenance (Fmd), costs that are
proportionately so much greater for species with low (e.g., cattle) than
with high (e.g., poultry) reproductive rate. Traits controlling N include
fertility, parturition interval, number of young per parturition and viability
of young. Viability may also be affected by the female's maternal ability in
terms of ease of parturition, temperament and especially milk production. Other
measures related to reproduction that can be important in difficult
environments include those for tolerance of heat or cold, resistance to ticks
and diseases, and ability to maintain body condition under sparse or variable
nutrient environments. The other meat output components, of course, are the
weight (Po) and the value per
unit of weight (Vo) for each market animal, the latter indicated by
measures of conformation and especially composition and eating
qualities.
Output from
culled adult females also reduces the net cost for young female replacements (R), which is determined by adult
mortality and culling for infertility or other failures, and the relative unit
value of young vs adult cull female weight. These factors also determine the optimum terminal age and severity of
culling for infertility of breeding females (e.g., Núñez-Dominguez et
al., 1992), which differs greatly among species.
Measures of
output from the female herself also include both quantity (Pd) and
unit value (Vd) of such products as milk, fiber and eggs. A wide
variety of measurements is usually required
to estimate value per unit of adult product output (Vd) (e.g.,
composition of milk, wool character, egg size and quality).Generally, in
species maintained for such specialized direct female output (e.g., dairy
cattle, water buffalo, sheep, goats, egg chickens), the total value of such
direct output may make income from progeny quite secondary. However, the
relative importance of direct and progeny output varies greatly with the
production-marketing system, from specialized meat or milk to dual purpose.
Feed intake is the major measure of input cost required in comparing
breeds and their crosses, but is much more difficult to obtain than measures of
output, especially for breeding females of
ruminant species. Feed intake for female maintenance (Fmd) varies
most with her body size and that for market progeny output 
varies with progeny
number (N), body size maintained (Fmo) and rate of growth (Fpo)
over days in the feeding period (D).
To the extent possible, direct measurement of feed intake is preferable to indirect estimates of feed intake, because it involves fewer assumptions. However, especially for grazing females of ruminant species, it is often necessary to estimate feed intake from experiments with subsamples of each breed or cross, or indirectly from measures of body size and composition plus product volume and composition, using prediction formulas based upon extensive published results of prior research on energy metabolism (e.g., Graham, 1967; Koong et al., 1985).
Direct measurement of feed intake for progeny from weaning (or
hatching) to market, is generally preferable and often feasible, except when
growing performance is measured on pasture. When feed intake cannot be
measured directly on growing market animals, it can be estimated from body
weights over the feeding period. Accuracy of feed intake estimates can be improved by obtaining body composition
and/or calorimetry measures of fasting heat production for subsamples
from each breeding group evaluated (e.g., Baker et al., 1991). Such basic
experiments with subsamples, including indirect or direct calorimetry, permit
detection of possible differences in maintenance requirements and its
association with body size and composition (Olthoff and Dickerson, 1989).
Non-feed costs for such items as labour,
housing, health care, interest on capital tend to be only partially
proportional to feed inputs. Estimates of changes in these costs with
increases in components of performance should
be included in evaluations to avoid upwardly biased evaluation of genetic effects
on production efficiency.
Improvements in such traits as fertility and mortality reduce feed and other
costs more than gains in female egg or milk production or growth rate of market
meat animals.
