M.T. Kuhn and J.L. Hutchison
Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350
2007 J. Dairy Sci. (?)
© American Dairy Science Association,
2007. All rights reserved.
Individuals may download, store, or print single
copies solely for personal use.
Do not share personal accounts or passwords
for the purposes of disseminating this article.
The objectives of this research were to
assess the utility of using multiple services, rather than first service only,
and an expanded service sire term for prediction of bull conception rate (CR)
in the US. The intent with the expanded service sire term was to determine if
accuracy could be improved by estimating factors affecting the bull's CR
explicitly in the model and then formulating the bull's prediction as the sum
of his own service sire solution along with the solutions for the other
factors. Factors considered for the expanded service term included age of the
bull at the time of mating, stud, inbreeding of the service sire, inbreeding of
the mating (potential embryo), and an additive genetic effect. Both simulated
and field data were utilized to study the objectives. In simulation,
predictions were compared to true values while with real data, predictions were
compared to bulls' average CR in set aside data. Field data included 3,312,998
breedings for 737,626 Holstein cows in 1,419 herds distributed over 43 states
and across 12 yr (1995 to 2006).
The use of
both multiple services and an expanded service sire term improved accuracy of
predictions. Multiple services contributed a 7 to 9% increase in accuracy while
the expanded service sire term improved accuracy by an estimated 12%. The
amount of improvement in accuracy depends on the number of services available
for the bull but even for bulls with at least 500 matings, the combination of
multiple services and an expanded service sire term can be expected to result
in an overall increase in accuracy of at least 20%. Mean differences between
predictions and bulls' average CR in set aside data indicated that this
improvement in accuracy can be brought about without introducing bias into the
evaluations. Heritability estimates were essentially zero. Thus, use of an
additive genetic effect for the service sire will not be of assistance in
prediction of bull fertility. All 4 of the other factors used in the expanded
service sire term contributed to improved accuracy, although age of bull at the
time of mating was, by far, the major factor. Allowing the stud effect to vary
by year and using only the stud's most recent year solution in prediction was
shown to be superior to using just stud alone; i.e., than assuming stud effects
were constant over time. Furthermore, exclusion of stud*year from predictions
reduced accuracy by about 6%.
(Key words: Bull fertility; Conception rate; prediction; artificial insemination)