Genetic Evaluation

18 September, 2015rodster385Comments (0)

1 The genetic potential of dairy goats to produce milk and fat can be
improved each generation if does and bucks with the best genotypes in
the current generation are selected as parents for the next generation.
The practical difficulty in mating ''the best to the best'' is to
evaluate which does and bucks are ''the best''.

2 Does
A doe's production is the result of both genetic and environmental
factors. Methods have been developed to adjust for some of the
environmental effects on production. Adjustment is necessary to
measure a doe's genetic ability accurately. Records are adjusted to
remove bias due to the effects of age and season at kidding and to
project incomplete records to a standard 305-day basis.

3 Many environmental factors are common to does kidding in the same
herd and year (herd-year). Comparisons among does freshening in the
same herd-year are not affected by such factors. However, comparisons
among does in different herd-years should be based on differences
between does' individual production and production of other does in
the same herd-year; i.e., herdmate deviations. Genetic differences
among herds could be corrected by considering the genetic values of
herdmate sires. This correction becomes more effective as the accuracy
of the evaluations of herdmate sires increases.

4 Bucks
Evaluation of bucks for milk traits is more complicated than
evaluation for growth, meat, and fiber traits or evaluation of does
because bucks do not produce milk. Information on milk traits for a
buck comes from observations on female relatives, particularly
daughters. One buck's genetic ability to sire superior daughters can be
compared with another buck's ability if both have daughters kidding in
the same herd-year. Indirect comparisons also are possible. For
example, if two bucks have daughters in different herd-years but in
common with daughters of a third buck, the two bucks in question can
be compared through the third buck. Thus, daughters of bucks used in
more than one herd-year serve to tie evaluations together. A buck
cannot be evaluated properly if he does not have daughters in a common
environment with daughters of another buck; i.e., if he is the only
buck with daughters in a herd-year and has daughters only in that
herd-year. Artificial insemination (AI) can increase the number of bucks
in different herd-years and thereby increase the accuracy of buck
evaluations. Furthermore, AI may be the most practical way to use
several bucks in a herd each year and for many bucks to have daughters
in more than one herd.

5 Generally, a genetic evaluation of a buck is an estimate of the
amount by which a buck's daughter production differs from production of
daughters of bucks chosen as the base group. More daughters records
provide more information; however, the distribution of daughter records
among herd-years and the number of comparisons with daughters of other
bucks determine the amount of information each record provides. The
prediction of performance of future daughters varies with the amount of
information available as well as with the level of current daughter
performance.

6 Research to evaluate dairy goat bucks is progressing. Recent data
show that the number of lactation records received for genetic
evaluations increased from 2,858 in 1974 to 7,516 in 1977 and that the
number of herds increased from 389 to 1,171. The number of lactations
per herd-year, however, decreased from 7.3 to 6.4. This drop was
probably a result of an increase in the number of smaller herds on test
in recent years. Of the 4,853 herd-years in the data, 942 (19.4) had
only 1 buck represented per herd-year. About 530f the herdyears had
fewer than four bucks represented. Of the 10,102 bucks, 5,608 (55.5)
had only 1 daughter record. About 87had fewer than four daughters
records. A total of 9,812 bucks had daughters in herd-years with
daughters of other bucks and thus had information suitable for
daughter comparisons. Among these tied bucks, 5,068 (51.7) had
daughters in only 1 herd-year. The number of dairy goats enrolled in
testing plans has increased to 14,449 does and 1,616 herds as of
January 1, 1982.

7 A dairy buck summary with evaluations for 143 Alpine, 205 Nubian,
72 Saanen, and 82 Toggenburg bucks was published by the University of
California at Davis in the fall of 1980; lists of elite bucks and does
also were published. Data for the summary came from official Dairy Herd
Improvement records from California for 1970 to 1978 on file at USDA.
Records of bucks with fewer than four daughters could not be used
because of the limited reliability of the evaluations. Predicted
differences for milk yield, fat yield, and fat percentage were given,
along with their standard errors. The base was established so that an
average buck's evaluation was zero. Bucks and does with evaluations at
least one standard error above averages for milk or fat were designated
as elite.

8 Genetic evaluation is an evolving process. Preliminary
identification of some superior bucks should encourage their widespread
use. As a consequence of this, bucks could be evaluated more accurately,
which would promote genetic progress.

9 Young Buck Proving Scheme
The possibility of a national program for buck evaluation is
becoming more likely, but poor distribution of daughters across herds
or years impedes progress. Breeders interested in having their bucks
included in a future summary can take several approaches to insure that
their bucks have the information needed:

(1) Breed a buck to does in several herds. Trade breedings with
other buck owners so that each buck will have daughters in several
herds. Some herd owners offer incentives, such as lowered stud fees, to
other herds on official test and classification.

(2) After daughters of a buck are born, distribute them to
different herds. A buck-proving cooperative made up of several herds
might test daughters of four or five young bucks by trading daughters
until several from each sire are in each herd. This system might be
preferable to trading breeding services if herds are long distances
apart.

(3) Raise daughters until fall, breed them to a young buck other
than their sire, and then trade or sell them to other herds on test. In
this way, daughters freshen in other herds and are compared with
daughters of other bucks.

10 In establishing and following any young buck proving scheme,
several points must be kept in mind:

(1) Five daughters each in five herds is considered a minimum goal
for a buck to be evaluated.

(2) Daughters must be in tested herds with daughters of other
bucks.

(3) Bucks should be bred to several does so that the choice of
mates will not favor a certain buck.

(4) Unbiased cooperation of herd owners is necessary, but the
opportunity to identify bucks that have the potential for true breed
improvement makes it worth the effort.

11 A young buck proving scheme could be implemented immediately and
would have great benefits for the dairy goat industry in the United
States and around the world.