GENETIC PROGRESS OF AMERICAN YORKSHIRE SWINE
M.T. See,
J.W. Mabry[1],
J. Venner[2],
T.J. Baas[1], K.J. Stalder[3],
and S.J. Moeller[4]
Summary
Performance records collected by
the American Yorkshire Club from 1988 to present were evaluated to report
annual genetic progress. Since
1988, the average breeding value for number of pigs born alive, number of pigs
weaned and litter weight at 21 days has improved .36 pigs, .10 pigs and 3.6 kg,
respectively. The Sow Productivity Index and the Maternal Line Index have increased
5 and 17 index points, respectively. Regression coefficients indicating average
annual improvements in breeding values for backfat depth, loin muscle area,
days to 144 kg and kg of lean in an 84 kg carcass were -.06 cm, .43 cm2,
-.45 days, and .21 kg, respectively. These results would indicate that genetic
improvement has been achieved simultaneously for both reproductive and
post-weaning traits.
Introduction
The American Yorkshire Club has
been progressive in implementing and utilizing across-herd genetic evaluations
for improving both maternal and terminal characteristics. Maternal selections
are based upon the reproductive traits of number of pigs born alive (NBA),
litter birth weight, number of pigs weaned (NWN) and litter weight at 21 d of
age (LWT). Results from the most
recent national genetic evaluation that included data from 1985 to 1999 were
used to determine genetic trends in the breed.
Materials and Methods
Breeding values (BV) for NBA, NWN
and LWT were estimated using an animal model that includes fixed effect of
contemporary group (CG), random direct genetic effect of the animal and
uncorrelated random effects of sow's permanent maternal environment and mate
within CG. Contemporary groups were defined by the producer as sows that were
bred, gestated, farrowed and weaned together. Data were pre-adjusted for known
sources of variation as described in (1). Components of (co)variance used for
BV estimation were specific for the American Yorkshire breed as described in
(2). Breeding values were also estimated for the post-weaning traits of days to
114 kg (Days), backfat depth (BF), loin muscle area (LMA), and kg of lean in an
84 kg carcass (Lean) using a model that includes fixed effects of CG and sex
within herd, the random genetic effect of pig, and uncorrelated random effect
of the pig’s birth litter. All post-weaning data were adjusted to 114 kg as
described in (2). Traits were combined into three selection indexes: Sow
Productivity Index (SPI) including only reproductive BV, Maternal Line Index
(MLI) including all BV, and Terminal Sire Index (TSI) including only
post-weaning BV. Maternal BVs were
estimated for 115,647 pigs and post-weaning BVs were estimated for 357,349
pigs. As there was little change in BVs prior to 1988 when substantial usage
and availability of BVs occurred, genetic trends were estimated by regressing
mean BV on year of birth using a spline model (3) with a knot at 1988. The
spline model results in separate genetic trends for animals born prior to and
after 1988.
Figure 1. Genetic trend for number of pigs born alive breeding value
Figure 2. Genetic trend for number of pigs weaned breeding value
Figure 3. Genetic trend for litter weight at 21 days breeding value
Results and Discussion
Since
1988, the average BV for NBA, NWN and LWT
(Figures 1 to 3) has improved .36 pigs, .10 pigs and 3.6 kg,
respectively. The SPI (Figure 4) and MLI (Figure 5) have increased 5 and 17
index points, respectively. Regression
coefficients indicating annual genetic improvement for NBA, NWN, LWT, SPI and
MLI between 1988 and 1998 were .036 pigs, .01 pigs, .38 kg, .52 index points,
and 1.73 index points, respectively. Prior to 1988 annual genetic improvement
for NBA, SPI, and MLI was .02 pigs, .17 index points, and -.32 index points,
respectively.
Figure 4. Genetic trend for sow productivity index (SPI)
Figure 5. Genetic trend for maternal line index (MLI)
Regressions for NWN and LWT prior to 1988 were not significantly different from zero.
Regression coefficients for the post-weaning traits (Figures 6 to 10) of BF, LMA, Days,
and Lean were -.06 cm, .43 cm2, -.45 days, and .21 kg, respectively.
These results would indicate that genetic improvement has been achieved
simultaneously for both reproductive and post-weaning traits.
Figure 6. Genetic trend for backfat depth breeding value
Figure 7. Genetic trend for loin muscle area breeding value
Figure 8. Genetic trend for days to 114 kg breeding value
Figure 9. Genetic trend for kg of lean in an 84 kg carcass breeding value
Figure 10. Genetic trend for terminal sire index (TSI)
Implications
American
Yorkshire breeders have made significant genetic improvement for economically
important reproductive traits by implementing effective across-herd selection
programs. Genetic improvement of reproductive traits should help improve the overall
efficiency and profitability of pork production.
Literature Cited
(1) Culbertson, M. S., J. W. Mabry, J. K. Bertrand and A. H. Nelson.
1998. J. Anim. Sci. 75:2362-2367.
(2) Mabry, J.W. 1998. Seedstock Edge 5:45-49 (no.4). West Lafayette, IN
U.S.A.
(3) Freund, R. J., and R. C. Littell. (1991) SAS
System for Regression 2nd Edn, SAS Institute, NC.
