PROCEEDINGS - American Society of Animal Science

estimate of the relative revenue and cost information
associated with the use of each candidate bull. The objective
of this study was to use this decision support tool, in
conjunction with field data derived from a cow-calf
operation, to examine the costs and benefits associated with
deriving on-ranch weaning weight (WW) expected progeny
differences on terminal sires using weaning weight data from
a single calf crop, and DNA-based paternity designations.
Materials and Methods
Animal and ranch operation. The field study data was
collected from the UC Davis commercial cow-calf herd
housed at the Sierra Foothills Research and Extension Center,
Browns Valley, California. Herd size is typically ~300 cows
and cows calve during the fall months (September through
November). Cows are bred in the winter months and all bulls
passed a breeding soundness examination (BSE) by a
licensed veterinarian prior to the breeding season. At calving,
birth date, weight and dam ID are recorded, and a DNA
sample is collected. At approximately seven months of age
calves are weaned, weighed and a unique electronic
identification device (EID) tag is assigned. Two to four herd
bulls per breeding pasture were used and data was collected
over a three year period 2006-2008. Weaning weight data
was available on two of the calf crops. Some of the cows in
this research herd were bred using A.I., and so the average
number of open cows available per herd bull in this study was
lower than is typically seen on Western ranches where a 25
cow:bull ratio is common. Bulls remained with the cows for a
90 day breeding season.
DNA samples were genotyped with 62 (2006), or 99
(2007, 2008) single nucleotide polymorphism (SNP)
parentage panels (Igenity, Duluth, GA), and genotyping
results were used to match potential sires to their true
offspring. The calves sired by each bull in its breeding group
was expressed as a proportion of that expected if all bulls in
the pasture sired an equal number of progeny (e.g. expect
0.33 of the progeny to be sired by each bull if there were 3
bulls in the breeding group) for the three years of the study
(Figure 1).
A genetic evaluation of 519 weaning weight records
from two cohorts of progeny, sired by 23 herd bulls and 7 AI
sires, born in Fall 2006 and 2007 was carried out using a
maternal effects model of the form y = Xb + Zu + Z m u m +
Z p u p + e, where y is a vector of weaning weight records
adjusted by days of age at wean; X, Z, Z m , and Z p are
incidence matrices relating observations to fixed effects,
direct genetic effects, maternal genetic effects, and permanent
environmental effects; b, u, u m , and u p are vectors of fixed
effects, direct genetic effects, additive genetics effects on the
dam of each individual, and nonadditive and permanent
environmental effects due to the dam; and e is a vector of
residuals. The fixed effects used in this model were year, sex
and dam age (classified as 2, 3, 4, 5-10, and 11+ years of
age). Heritabilities used were 0.25 and 0.10 for direct and
maternal effects, respectively. The proportion of variance due
to permanent environmental effects was assumed to be 0.05.
Mixed model equations were solved using the MTDFREML
package (http://aipl.arsusda.gov/curtvt/mtdfreml.html;
accessed 3/31/09).
For the economic analysis, the cow-calf decision
support software (http://dss.ansci.iastate.edu) was used to
determine the value of one unit increase of WW EPD
assuming a terminal sire breeding system (i.e. no
replacement heifers kept). This was done by selecting the
herd input values outlined in Table 1, and selecting the
“Terminal Sire” breeding system. The cow genetics tab
was set to “Zero EPDs” which sets all cow herd EPDs to
zero. The status quo income, costs and capital value of the
herd was then displayed by selecting the proceed button.
To determine the value of selecting a bull with a one unit
increase in weaning weight EPD, “Bogus” was entered as
sire selection from the “Search Among” drop down menu,
and then “Relative Economic Values” was selected from
the “Type” drop down menu. The “Bogus” bulls are not
real bulls, but represent information that can be useful to
model the effect of changing the value of specific EPDs.
Upon activating the “Select Bulls” button, a series of
“bogus” bulls appeared. At this point the “REV WW”
(relative economic value of WW) bull was selected (+1.0
WW EPD) along with the “REV Base” bull which is a
bull with the value of 0 at all EPDs i.e. effectively the
same genetics as cow herd. Selecting the “Calculate
Perturbed Results” button resulted in an estimation of the
added annual income resulting from use of the REV WW
terminal sire. The value of one kilogram of WW EPD was
valued at ~$42 per year.
In our simple model we considered the cost of
DNA testing to be ~$500/bull (25 calves x $20/test) and
of culling a bull based on a poor resultant WW rEPD, and
then purchasing an average young sire to take his place
for the 3 breeding seasons that the original bull would
have been present in the herd. The breakeven in this
scenario was when the loss in the weaning weight from
the inferior bull for breeding seasons 3-5 equaled the cost
of the genotyping his first calf crop and purchasing the
new bull, minus the salvage value of the cull bull. We
calculated that to be when the inferior bulls WW rEPD
was ≤ -16.7 kg. If only steers were genotyped
(~$250/bull), then this value would drop to ≤ -14.7kg.
Table 1. Production, management, and economic input
values used for the simulated base herd
Model Parameters
Value
Herd size 300
Calving Rate 90%
Calf survival 95%
Mature weight
544 kg
Yearling weight
352 kg
Weaning weight
272 kg
Cows per bull 25
Maximum cow age, year 10
Incremental cow costs ($) 25
Heifer price ($)
2.11/ kg
Cow price ($)
1.11 kg
Calf price ($)
2.27/ kg
Bull price ($) 2,500
Years of service 5
Salvage Value of cull bull ($) 900