WHAT IS A BULL TEST?
Michael
J. Baker
Beef Cattle Extension Specialist
Cornell University
The
purpose of a Central Testing Program is to: 1) compare individual
performance of potential herd sires, 2) provide an opportunity
for seedstock producers to market individual bulls, 3) provide
a source of bulls for commercial and seedstock herds and 4)
provide an educational opportunity for sellers and buyers alike.
The
performance of animals grown on different farms should not be
compared due to differences in environment, feeding and management.
A Central Test removes the effect of these variables and allows
the comparison of performance of bulls from different farms.
The main trait measured in a central test is weight gain over
112 days. While much more information is provided which is valuable
in sire selection, the central test itself only "tests" or evaluates
gain for the 112-day period that the bulls are being fed.
Not
all bulls that complete the test will be sold. Of the 72 bulls
consigned, no more than 40 will sell. Bulls will not be allowed
to sell if they fail the following two exams:
Reproductive
soundness. Each bull will undergo an internal and external
exam, including a semen test, to evaluate his potential to breed
females. A passing score indicates that from a reproductive
standpoint, he is determined structurally fit to breed. Libido,
which is his desire to find and service females in heat, will
not be determined.
Structural
soundness. A herd sire is expected to travel a lot of ground
to fulfill his duties in a short breeding season. Therefore
bulls will be evaluated for defects in feet and leg structure
that may inhibit their ability to service cows. As this evaluation
can be subjective in nature, leaving it open to criticism, it
will be completed by the sale management with no direct ties
to the consignors or the NYBPA.
Those
that pass the above tests will be ranked by an index which takes
into consideration average daily gain (ADG), weight per day
of age (WDA), ultrasound measured backfat (BF) and ultrasound
measured ribeye area (REA). These factors will be weighted to
represent the relative importance to the commercial industry:
ADG, WDA and REA will make up 90% of the index, the remaining
10% to be placed on BF. Bulls that rank 95 or better will be
eligible for sale.
SELECTING
A POTENTIAL HERD SIRE
Primary
Selection Criteria:
To
evaluate the data provided by a central bull test place emphasis
on these traits in the following order: 1) On Test ADG, 2) Adjusted
Yearling Weight, 3) Weight per-day-of-age and 4) Adjusted 205-day
weaning weight. As ratios are easier to compare, they are more
informative that the actual traits. Also to guard against the
inadvertent selection for large cow size, comparisons should
be made on bulls of the same frame score. Explanation of selection
terms is presented below.
Average
daily gain (ADG) and ratio on test are the most important
data from the test station because they measure growth only
during the period when all bulls are under the same test conditions.
Selection for test gain in bulls of the same frame size should
improve pre-weaning growth and thus weaning weights, because
some genes affect both traits. Selection of bulls for ADG with
out considering frame size results in selecting larger frame
bulls which, if you keep replacement heifers results in selecting
for larger frame cows. An individual's ADG ratio is calculated
by dividing his ADG by his breed contemporary group average
ADG and multiplying by 100. A ratio of 100 means the bull's
ADG is average. A 115 ratio means he gained 15% faster than
the average bull. A 90 ratio means he gained 10% slower than
the average bull. This ratio makes comparisons easier and is
more informative than actual ADG.
Adjusted
205-day weaning weights and within contemporary-group ratios
provide good comparisons of bulls from the same herd, but have
little value for comparing bulls from different herds. Weaning
weight is the best available estimate of a dam's milking ability.
Therefore, an adjusted 205-day weaning ratio of 100+ is desirable.
Adjusted
yearling weight and ratio combine adjusted weaning weight
and postweaning gain into a single composite measurement which
is highly heritable. The ratio is the best measure for comparing
growth of calves from the same herd. However, use care when
comparing adjusted yearling weights and ratios of bulls from
different herds, because the weaning weight portions of their
growth were made on different farms, not under comparable conditions.
Weight
per-day-of-age and ratio are alternative measurements of
growth during the same period, but do not include adjustment
for age of dam, which can be large. Therefore, these measurements
are biased by differences in age-of-dam, weaning age, preweaning
nutritional levels and length of the period from weaning until
the start of the test.
Additional
data for selection:
Keep
it all in perspective. When considering economic efficiency
(profit), remember that on a scale of 1-10, fertility scores10,
growth rate scores 2-3 and carcass traits score 1-2. Live calves
have a greater impact on profitability than dead high marbling
calves. Traits that affect fertility are breed, birthweight,
scrotal circumference, and stayability. Growth is measured by
on test ADG, weaning weight and yearling weight. Measures of
carcass traits are backfat, rumpfat, ribeye area and intramuscular
fat (marbling).
What's
your market?
· If calves are sold at weaning, place emphasis on growth traits.
· If calves are fed out and marketed as finished cattle, place
emphasis on carcass traits.
Purebred or crossbred?
If selling feeder calves and/or finished cattle, cross breeding
will increase hybrid vigor, which will increase weaning weight
as well as feedlot performance by as much as 20%. For example
a purebred cow bred to the same breed bull that weans a 500-lb.
calf will wean a 525-lb. calf when bred to a different breed
bull.
Which
breed?
· English: small, fertile, slow growth, less muscled, easy calving,
longer lived, higher marbling
· Continental: large, less fertile, high growth, high muscle,
hard calving, shorter lived, lower marbling
These are general terms; some breeds do not fall into
the English/Continental mold, partly due to modern genetics.
What frame size?
The retail meat industry prefers a 12-15 sq. in. ribeye and
a liveweight of 1100-1400 lbs. Bulls should be selected so that
when mated to cows, the steer progeny meet this retail preference.
· If cows are Frame Score 4, weigh less than 1100 lbs., or calves
are assigned a USDA feeder calf grade of Small, use a Frame
Score 6-7 bull.
· If cows are Frame Score 8+, weigh more than 1400 lbs., or
calves are assigned a USDA feeder calf grade of Large, use a
Frame Score 5 bull.
What
size ribeye?
Heavy bulls should have larger REA than lighter bulls. To reduce
this influence of weight REA should be evaluated based on live
weight of the bull. To meet retail meat industry standards of
a 12-15 square inch ribeye area, while keeping live weight in
an acceptable range, select bulls that have 1.0-1.4 sq. in.
REA per 100 lbs. of bodyweight.
What
about EPD's?
Expected Progeny Differences (EPDs) are extremely useful tools
for evaluating sires. See accompanying article for a brief description
on their use.
SUMMARY
Cow/calf
producers must do a thorough job of evaluating their cowherd
prior to selecting a bull. Based on this analysis, producers
should place emphasis on those traits that are lacking in their
herd, without compromising cow fertility. While a central test
station only collects data on a few traits, the additional information
provides a description of the bull that is valuable in selecting
your next herd sire.
TERMS
AND DEFINITIONS
ACC:
Accuracy is the reliability that can be placed on the expected
progeny difference (EPD). An accuracy of close to 1.0 indicates
higher reliability.
DOB:
Bull's date of birth.
BW:
is actual birth weight.
WW:
is the Adjusted Weaning Weight reported by the National Breed
Association.
Yrlg
Wt: is the 365-day Adjusted Yearling Weight.
Start
Wt: the average of weights taken on two consecutive days
at the start of the test.
End
Wt: the average of weights taken on two consecutive days
at the end of the test.
FE:
Feed efficiency computed as dry matter intake divided by gain
on test. Dry matter intake is determined using the bull's weight
and gain on test adjusted for environmental effects.
AdjFE:
Adjusted Feed Efficiency. This is the feed efficiency standardized
to the same stage of growth. As FE will vary depending on the
stage of growth, this is a more accurate figure to compare individual
bulls.
ADG:
Average Daily Gain. Total gain divided by the 112 days of the
test.
ADG
Ratio: indicates if a bull is superior or inferior in ADG
when compared to his test group mates. A Ratio of 100 is average.
A Ratio of 105 indicates that a bull's ADG is 5% better than
the average of the test group. A Ratio of 95 indicates that
a bull's ADG is 5% less than the average of the test group.
This ratio is only directly comparable within the bull's test
group of the same breed. Ranking shows which quarter this bull's
ADG falls into within his test group.
WPDA
Lbs: Weight Per Day of Age (WPDA) at the conclusion of 112
day test period, calculated by taking his final weight, less
his birth weight, divided by age in days at the end of test.
WPDA
Ratio: indicates if a bull is superior or inferior in WPDA
when compared to his test group mates. A Ratio of 100 is average.
A Ratio of 105 indicates that a bull's WPDA is 5% better than
the average of the test group. A Ratio of 95 indicates that
a bull's WPDA is 5% less than the average of the test group.
The ratio is only directly comparable within the bull's test
group of the same breed.
Frame:
Frame Score. Frame Score is a convenient way of describing the
skeletal size of cattle and it is a highly heritable trait.
SC:
Adjusted Scrotal Circumference listed in centimeters and adjusted
to one year of age using adjustment factors provided by each
National Breed Association. Bulls with larger scrotal circumferences
tend to have more desirable seminal characteristics and tend
to sire daughters that reach puberty at an earlier age. Ranking
shows which quarter this bull's ADJ SC falls into within his
test group. Any EPD listed below ADJ SC is the reported Scrotal
Circumference EPD from the bull's National Breed Association.
ADJ
PLVC: Adjusted Pelvic Area listed in square centimeters
and adjusted to one year of age.
RibFat:
Actual fat thickness measured above the location between the
12th and 13th ribs and expressed in inches. Any EPD listed below
RIB FAT is the reported Fat Thickness EPD from the bull's National
Breed Association.
%
Intramuscular Fat (%IMF): Percent Intramuscular Fat measured
between the 12th and 13th rib. This is an estimate of marbling
score, which is the major factor used in determining USDA Quality
grade. Values shown are actual and adjusted to 365 days of age.
If these bulls were steers, their values would be approximately
one point higher. While marbling is a graders estimate of the
amount of the flakes of fat on the surface of the muscle, %IMF
is an estimation of the total fat that also includes the fat
in the muscle not visible to the grader. These two measures
are not exactly correlated, however the table below provides
some guidelines for converting %IMF to USDA Quality grade. Any
EPD listed below % IM FAT is the reported Marbling EPD from
the bull's National Breed Association.
Ribeye
Area (REA): Ribeye Area measured between the 12th and 13th
ribs and expressed in square inches.
ADJ
REA: is the bulls Adjusted Ribeye Area. This is the Actual
REA adjusted to one year of age using adjustment factors (when
available) provided by each National Breed Association.. Any
EPD listed below ADJ REA is the reported Ribeye Area from the
bull's National Breed Association.
REA/Cwt:
Ribeye area per hundred pounds of body weight calculated
by dividing 365-day weight into adjusted REA times 100. This
is an indication of muscling corrected for weight of the bull.
FINAL INDEX: is a combined "index" for that bull. It
is calculated as follows: .30(ADG Ratio) + .30(WPDA Ratio) +
.10(Backfat Ratio) + .30(REA per 100 lb body weight ratio).
This indicates what the bull's combined performance was relative
to his test group within breeds. Bulls with high FINAL INDEXES
should add more growth and muscle potential to calves than bulls
of the same breed with lower values.
EXPECTED
PROGENY DIFFERENCES
Expected
Progeny Differences (EPDs) are valuable in comparing animals
within a breed. Some studies suggest that EPD's are as much
as seven times more accurate in predicting progeny performance
than the individual's own records. This is a result of the fact
that EPDs are constructed using the performance of all available
relatives along with the individual's own record. These relatives
could include ancestors, siblings and progeny.
An
EPD can be constructed for any trait that a National Breed Association
chooses to measure. The most common are Birth Weight, Weaning
Weight, Yearling Weight and Milk. Milk is measured by statistically
separating weaning weight differences into a component due to
growth genes and another due to differences in milk production.
EPDs have also been constructed by breeds for calving ease,
scrotal circumference, mature size, ribeye area, carcass weight,
marbling score, disposition and others. Every EPD value on a
bull has an accompanying accuracy. The accuracy value tells
how reliable the EPD value is. Accuracy values range from 0
to 1. A bull with an EPD accuracy close to 1 will change very
little, while a bull with an accuracy closer to 0 has the potential
to change more. Yearling bulls generally have lower accuracy
values because their EPDs are based on previous generations
and have yet to be validated using data from actual progeny.
Every breed that published EPDs also publishes a table that
shows how much an EPD is likely to change at a given accuracy.
The accuracy of the EPD improves as the number of records from
which it is calculated increases.
It
is rare that cattle will excel in all or even most of these
EPDs. Breeders should select cattle with the traits they wish
to emphasize or to improve deficiencies in their herd. EPD values
are not an absolute guarantee of how calves from a particular
bull are going to perform. The heritability of beef performance
traits range from 20 to 50 percent. This means that 50 to 80
percent of all the variation seen in calf performance is due
to environmental or other factors. EPDs are a great management
tool that should be used by all cattlemen when making breeding
decisions.
The
key word when using EPDs is DIFFERENCE; therefore they should
be used when comparing two or more potential sires from the
same breed. For example:
Birth
weight (BW) Calves sired by Bull B will weigh 6.5 pounds
less at birth on average, than calves sired by Bull A.
Weaning
Weight (WW) and Yearling Weight (YW) Calves sired by Bull
A would, on average, weigh 14 and 25 pounds more than calves
sired by Bull B for weaning and yearling weights, respectively.
Maternal
Milk (MM) Maternal Milk EPD applies to calves sired by the
individual bull and is an estimate of differences in weaning
weights due to differences in milk production.
The
table below lists the average EPDs by breed. To compare bulls
within a breed, compare the bull's EPD in this catalog to the
breed average in the table. For instance, if you are looking
for a bull to improve milk production, use a bull with an above
average EPD for milk. To compare bulls between breeds, use the
Across Breeds EPD table printed in the subsequent article.
2003
ACROSS BREED EPD TABLE
The table of adjustment factors to estimate across-breed expected
progeny differences (AB-EPDs) for seventeen breeds was presented
to the Genetic Prediction Committee at the Beef Improvement
Federation Annual Meeting in Lexington, Kentucky, May 30 12
(see table). Animals of different breeds can be compared on
the same EPD scale, after adding the appropriate adjustment
factor to expected progeny differences (EPDs) produced in the
most recent genetic evaluations for each of the seventeen breeds.
For
example, if a Shorthorn bull has an EPD for weaning weight of
+15.0 and a Simmental bull has an EPD of +15.0, would we expect
this progeny out of a different breed of dam (e.g., Angus) to
weigh about the same? No, not unless the adjustment factor is
about the same. In this case the AB-EPD for the Shorthorn bull
is 46.2 which is the table adjustment factor of 31.2 added to
the Shorthorn bull's EPD of +15.0. The AB-EPD of the Simmental
bull is 36.6, the table adjustment of 21.6 added to the Simmental
bull's EPD of 15.0. In this example, progeny of the Shorthorn
bull would be expected to weigh, on average 9.6 lb more at weaning
than progeny of the Simmental (15.0 + 31.2) - (15.0 + 21.6)
= 9.6 lb.
The
AB-EPDs are most useful to commercial producers purchasing bulls
of two or more breeds to use in systematic cross breeding programs.
Uniformity from one generation to the next can be improved by
selection of bulls with similar AB-EPDs. Uniformity, is especially
important in selection of bulls for use in rotational cross
breeding systems for traits such as birth weight to manage calving
difficulty, and for traits related to cow size and milk production
to effectively manage feed requirements in cow herds. Divergence
of AB-EPDs for growth traits should be emphasized in selection
of bulls for terminal cross breeding. Divergence in AB- EPDs
should be considered in selection of bulls for use on first
calf heifers, emphasizing lower birth weights.
EPDs
are published annually by breed associations for most breeds
of beef cattle. EPDs can be used to estimate differences expected
in performance of future progeny of two or more individuals
in the same breed for birth weight, weaning weight, yearling
weight, maternal weaning weight, and milking ability (as reflected
in progeny weaning weights). Without the across breed adjustment
factors, EPDs can not be used to compare animals of different
breeds because they are computed separately for each breed and
each breed has a different base point. The adjustment factors
not only reflect current breed differences but also differences
in the base (EPD = 0) of each breed. Thus, adjustment factors
alone cannot be used to estimate average breed differences.
The
adjustment factors were updated using EPDs from the most recent
national cattle evaluations conducted by associations of each
of the sixteen breeds. The table is based on "head to head"
comparison of the breeds at the U.S. Meat Animal Research Center
(MARC), Clay Center, Nebraska. Brangus and Beefmaster were included
in the analysis for the first time this year. Adjustment factors
are not yet available for Brangus and Beefmaster MILK. The analysis
was conducted by MARC Research Geneticists Dale Van Vleck and
Larry Cundiff.
Questions may be addressed to:
Larry
V. Cundiff (402-762-4171) email address: Cundiff@email.marc.usda.gov
or
L. Dale Van Vleck (402-472-6010) email address: lvanvleck@unlnotes.unl.edu
DETERMINING
FEED EFFICIENCY FOR
INDIVIDUAL BULLS FED IN GROUPS
M.J.
Baker, L. O. Tedeschi and D.G. Fox
Animal Science Department, Cornell University
Feed costs represent two thirds of the total cost to produce
a finished steer. Computer simulations show that a 10% improvement
in feed efficiency can result in a 43% improvement in feedlot
profit. At low Choice, it takes nearly one half gallon of oil
every day to support a feedlot steer. Reducing the amount of
feed required to produce a pound of gain is a high priority
to cattle producers. Fortunately, feed efficiency is highly
heritable at 40%.
Feed conversion is the ratio of feed consumed to weight gain.
Until recently it has been cost prohibitive to measure feed
consumption on an individual basis under the commercial conditions
of a central bull test program. Recent improvements in predicting
the impact of environmental conditions on maintenance requirements
and in determining the composition of gain has led to the development
of a model that can accurately allocate feed to individuals
in group pens. The model described is the one used to compute
the feed efficiency value that is printed in this catalog. The
model is called the Cornell Value Discovery System (CVDS).
Computing
feed intake. The amount of feed consumed is determined by
an animal's requirement for maintenance and growth. Maintenance
is composed of those activities that keep the animal alive:
constant body temperature, operation of internal organs, activity
required for finding and consuming feed, etc. The maintenance
requirement goes up or down depending on temperature, body size,
level of activity, physiological age, breed and sex. Feeding
an animal just to meet its maintenance requirements results
in no change in body weight. When an animal gains weight however,
it now has a requirement for growth. Each unit of weight gain
is composed of fat and protein (muscle). As an animal matures,
the composition of the gain changes: younger animals have more
protein while older animals have more fat in the gain. Because
it takes more energy to put on fat than it does protein the
composition of gain will effect how much feed is required. By
accurately describing the animal's size, environmental conditions,
and growth rate, the amount of feed required is simply the sum
of the feed required for maintenance (FFM) and the feed required
for growth (FFG).
The
CVDS model has been built and validated using research from
hundreds of feeding trials using individually fed animals and
explains 83% of the variation that occurs in feed efficiency.
While the predictive capability of the model is high, it is
important to understand how to use the data to evaluate potential
herd sires.
Stage
of growth. The bulls evaluated on this test will be at different
stages of growth, because of differences in initial age and
weight, and rate of gain during the test. Recall that the feed
required for growth is affected by composition of gain. Composition
of gain is affected by stage of physiological maturity. Two
bulls born on the same date can be at two different stages of
maturity. A bull that has an ADG of 4.0 lbs. will be closer
to reaching his mature size (therefore "older") than the same
bull having an ADG of 3.0 lbs. Though these bulls have the same
chronological age, they have different physiological ages.
Comparing
bulls. The model uses the individual's growth rate to determine
at what stage of growth the animal is in. The stage of growth
will affect the requirement for growth by increasing the nutrient
requirement of bulls that are closer to their mature size. This
is done, because these "older" bulls have more fat in their
gain, which has a higher requirement than bulls with less fat
(i.e. younger) in the gain. Put another way, a bull that is
younger will require less feed per pound of gain compared to
one that is older, physiologically. Therefore comparing bulls
that are in two different stages of growth can lead to erroneous
conclusions. Just as we adjust weight to a common age (365 days)
we adjust feed efficiency to a common stage of growth. Therefore,
bulls must be compared by their adjusted value not their actual
value.