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GENETIC EVALUATIONS


COLLECTION: GOAT HANDBOOK
ORIGIN: United States
DATE INCLUDED: June 1992

Extension Goat Handbook

This material was contributed from collections at the National Agricultural Library. However, users should direct all inquires about the contents to authors or originating agencies.

DOCN 000000029
NO D-3
GENETIC EVALUATIONS
G. R. Wiggans; ARS-USDA Beltsville, MD M. Grossman; U. of Illinois Urbana M. R. Dentine; North Carolina State U., Raleigh
G. F. W. Haenlein; U. of Delaware, Newark.
Genetics and Reproduction

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.


GENETIC EVALUATIONS
COLLECTION;GOAT HANDBOOK
ORIGIN;United States
DATE_INCLUDED;June 1992


 
 


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