262 S
. Hermesch et al. Livestock Production Science 65 2000 261 –270
Kanis, 1994. However, an increase in litter size The proportion of crossbred litters for the first three
appears to be associated with decrease in piglet birth parities were 60.3, 64.4 and 74.2 for Large White
weight and survival Haley et al., 1988. Rydhmer et sows and 52.0, 56.2 and 69.1 for Landrace sows.
al. 1992 found that a low average piglet weight at Each litter originated from the first mating only and
birth increases piglet mortality. Therefore, in order to the proportion of litters from artificial insemination
increase the number of piglets weaned per sow was 18.3, 23.0 and 24.8 for the first to third parity.
through genetic improvement further reproductive The farrowing age for the first litter was restricted to
traits of the sow including litter birth weight, average 270–500 days. Age of litter when litter weight was
piglet weight at birth and 21-day litter weight should recorded ranged from 10 to 28 days with a mean of
be considered in breeding programs. In addition, 19 days.
these reproductive traits might have stronger genetic Reproductive traits were analysed as a different
relationships with other production traits as currently trait in the first, second and third parity and included
assumed. Knowledge about genetic parameters be- number of piglets born alive NBA
, litter birth
1,2,3
tween reproduction traits and other performance weight LBW
, average piglet weight at birth
1,2,3
traits is mostly limited to growth rate, feed intake ABW
and litter weight at 21-days in the first
1,2,3
and backfat Short et al., 1994; Rydhmer et al., 1995; parity LW21 . Records available for 21-day litter
1
Tholen et al., 1996; Crump et al., 1997 with varying weight recorded in the second and third parity were
estimates between studies and data sets. Breeding not sufficient to analyse them as separate traits.
programs consider a number of production, carcase Furthermore, recording procedures for litter birth
and meat quality traits, and their genetic relationship weight and consequently average piglet birth weight
with reproductive traits is required in order to changed in the third quarter of 1993 when litter
establish whether reproductive traits should also be weight was recorded 3 days after birth. In total,
analysed in a multitrait analysis. The objective of 13 518 litters were available for analysis.
this study was to obtain genetic parameters for reproductive traits of the sow and to obtain genetic
2.2. Production, carcase and meat quality data correlations between reproduction traits and product-
ion, carcase and meat quality traits. Analysis of production, carcase and meat quality
data was based on performance records from 1799 Large White and 1522 Landrace boars. Performance
2. Material and methods traits comprised growth rate from three to 18 weeks
ADG1. Animals were performance tested from 18 2.1. Reproductive data
to 22 weeks providing information about growth rate during station testing ADG2, feed intake FDINT
Data from 3776 Large White and 2274 Landrace and feed conversion ratio FCR. Animals were
sows which farrowed between 1991 and March 1995 group penned until 18 weeks of age. The housing
were used to obtain genetic parameters for reproduc- system in the test station consisted of single penning.
tive traits of the sow recorded in the first, second and Animals were slaughtered at 22 weeks of age.
third parity. The pedigree data set of these sows Carcase traits included backfat at P2 site and backfat
included 150 Large White and 102 Landrace sires as and muscle depth between the third and fourth last
well as 1284 Large White and 715 Landrace dams. ribs recorded on the live animal as well as on the
Although animals were raised in the same unit, sows carcase LFDP2, LFD3 4, LMD3 4, FDP2, FD3 4.
farrowed in two different units. The proportion of Further carcase traits consisted of weight of the
sows farrowing in unit two was 67.1, 78.7 and 88.0 whole back left leg and the slash boned ham BLW,
in the first, second and third parity. As another LMW. Meat quality traits included pH recorded 45
editing restriction, only purebred litters or crossbred min and 24 h after slaughter pH45, pH24, colour of
litters from Large White sows and Landrace service the m
. longissimus dorsi and m. multifidus dorsi sires LWLR or Landrace sows and Large White
CLD, CMD, drip loss percentage DLP and service sires LRLW were included in the data set.
intramuscular fat content IMF. The fixed effect
S . Hermesch et al. Livestock Production Science 65 2000 261 –270
263
models included date of recording all traits, breed and quadratic covariable, and time period from
not significant for ADG2, FDINT, FCR, pH24 and farrowing to weighing linear covariable. The num-
CMD and parity ADG1, ADG2, BLW, LMW. ber of piglets weighed represented the sow’s own
Weight of the animal at test beginning was fitted for piglets as well as piglets that were cross-fostered
feed intake and feed conversion ratio. Backfat mea- from other sows. Breed of service sire was not
surements, muscle depth and intramuscular fat con- significant for any reproductive trait.
tent were corrected for weight of the animal at Only a small proportion 1–3 of the total
slaughter. Litter was fitted for growth rate and back variation was explained by the fixed effect model for
leg weight traits as an additional random effect. A number of piglets born alive. In contrast, the fixed
detailed description of the data structure and the effect model explained 53–63 of the total variation
analysed traits was given in Hermesch et al. 2000a for litter birth weight and 30–48 for average piglet
along with derivation of the appropriate model and weight at birth. These high coefficients of determi-
heritability estimate for each trait. Furthermore, nation were mainly due to farrowing season and
genetic correlations between these traits were pre- were caused by a change in performance recording
sented in Hermesch et al. 2000b. of litter birth weight. Since October 1993, litter birth
weight has been recorded 3 days after farrowing and 2.3. Analysis
therefore includes piglets that were cross-fostered. In addition, comparing least-squares means of farrow-
The significance of fixed effects fitted in the model ing seasons showed that litter birth weight increased
for each trait was analysed using PROC GLM SAS, by 3 kg from March 1992, but no explanation could
1991. Significant fixed effects included in the be given for this increase which was probably caused
models to analyse reproductive traits of the sow were by a change in recording procedure.
farrowing season which was defined in 3-month Variance components were obtained from an ani-
periods within year, breed of the sow, farrowing unit mal model with restricted maximum likelihood pro-
and whether the sow was artificially inseminated or cedures DFREML, Meyer, 1997 which provides
naturally mated Table 1. Covariables fitted for approximations of standard errors for heritabilities
reproductive traits included the age at farrowing and genetic correlations. Whenever the approxima-
linear covariable, number of piglets weighed linear tion of standard errors for genetic correlations failed
Table 1
2 a
Fixed and random effects for reproductive traits of the sow and total variation explained by fixed effects R Fixed effects
Random effect
2
R FS
breed AI
FU FA
n Period
Animal NBA
0.02 ✓
1
NBA 0.03
✓
2
NBA 0.01
✓
3
LBW 0.43
✓
1
LBW 0.51
✓
2
LBW 0.44
✓
3
ABW 0.30
✓
1
ABW 0.45
✓
2
ABW 0.48
✓
3
LW21 0.26
✓
1 a
NBA , litter size in the first to third parity; LBW
, litter weight in the first to third parity; ABW , average piglet weight in the
1,2,3 1,2,3
1,2,3
first to third parity; LW21 , litter weight at 21-days in the first parity; FS, farrowing season; AI, artificial insemination; FU, farrowing unit;
1
FA, age at farrowing linear covariable; n, number of weighed piglets for LW21 linear and quadratic covariable; Period, period of time
1
between farrowing date and weighing date of litter linear covariable. P , 0.01; P , 1.0; P , 5.0.
264 S
. Hermesch et al. Livestock Production Science 65 2000 261 –270
to converge, standard errors for genetic correlations weights in the second and third parity with estimates
were obtained using the formula of Robertson of 0.22 and 0.20. A lower genetic variance rather
1959. than an increase in environmental variance is the
Significant random effects were tested with a log cause for this reduced heritability for litter birth
likelihood ratio test. For reproductive traits of the weight in the first parity. Gilts were farrowing at 337
sow only maternal effects were analysed as an days on average and their uterine capacity is smaller
additional random effect. Only 19 of all sows with in comparison to multiparous sows. This might have
records had at least one full sister available in the been a restriction on expression of their genetic
data set and the data structure did not allow to fit potential in litter birth weight. Heritabilities were
litter effect as an additional random effect. General- 0.15, 0.16, 0.15 for average piglet birth weight in the
ly, maternal effects were not significant for reproduc- first three parities.
tive traits of the sow and were therefore not fitted in Literature estimates of heritabilities for litter birth
the model. weight and average piglet weight at birth varied
between research data and field data. Heritabilities for litter birth weight were 0.13 and 0.21 in the study
3. Results and discussion of Crump et al. 1997, which was based on field
