68 P
. Tummaruk et al. Livestock Production Science 68 2001 67 –77
of the Hampshire breed have been reported Rico, east. The variation within year in outdoor tempera-
1988 and no such study has been made in Sweden. ture as well as in photoperiod is relatively high for
It is well established that productivity of an this region. The outdoor temperature 24-h averages
individual sow depends on a number of reproductive in this area recorded during a period of 1994 to 1997
parameters, such as litter size at birth, weaning-to- ranged from a minimum of
2 14.48C in winter to a first service interval WSI and conception rate
maximum of 26.6 8C in summer. Day length varied
Britt, 1986; Stein et al., 1990. The variation in from about 18.6 h in June to 5.9 h in December.
these parameters is influenced by both genetic back- However, Swedish swine producers usually try to
ground of the sow reviewed by Rothschild and control the variation in photoperiod by supplying
Bidanel, 1998 and environmental factors, such as artificial light to give approximately 14–16 h light
management and season Clark and Leman, 1986; day in the sow units throughout the year. To obtain
Dewey et al., 1995. Significant interaction between information concerning herd management, directed
genotype of the sow and environmental factors has questionnaires were distributed to the herds included
been observed reviewed by Christenson, 1986. in the data analysed. For all herds, gilts were mated
Recent studies have demonstrated that reproductive in their second observed oestrus or later at about 7 to
characteristics of Swedish Landrace and Swedish 9 months of age. In most herds, dry sows were
Yorkshire sows are differently influenced by factors grouped in loose-housing systems with deep straw
such as season, parity and mating type Tummaruk et bedding and individual feeding, whereas lactating
al., 2000a,b. Although the Hampshire breed is used sows were kept separately in farrowing pens. Preg-
mainly as a sire line in crossbreeding, information nancy detection was performed about 4 weeks after
about their reproductive performance as purebreds is mating. Batch-wise production was performed in all
still of great interest. A number of studies has shown herds, i.e., a group of sows entered the farrowing
that the Hampshire breed has a smaller litter size unit on the same day, and all sows in that batch were
than the European white breeds, such as the Land- weaned on the same day. After weaning, the sows
race or Yorkshire Schneider et al., 1982; Bass et al., were immediately transferred to the mating gestation
1992; See et al., 1993. Number of piglets born alive units. During lactation the animals were either fed
per litter for Hampshire sows has been reported to according to a Swedish standard level, e.g., 8 kg day
vary from about 7.4 Rico, 1988 to 9.4 piglets Bass 12 MJ kg for a sow with 10 piglets Simonsson,
et al., 1992. To our knowledge, no study on fertility 1994, or fed ad libitum. During gestation the sows
traits such as WSI, remating rate, farrowing rate and were fed 2 to 2.5 kg feed day. The reasons for
age at first farrowing for Hampshire sows has been culling the sows were in most cases due to low
published. breeding value or poor conformation. In all herds, a
The objective of the present study was to re- number of crossbred litters about 10 were also
trospectively analyse the variation in reproductive produced by crossing Hampshire sows with York-
performance of purebred Hampshire sows with re- shire or Landrace boars. The crossbred litters were
spect to parity influence and seasonal variation. The excluded from the statistical analyses, but results
effects of lactation length and WSI on subsequent from crossbred matings were included when analys-
fertility were also analysed. ing farrowing rate and remating rate.
2.2. Data analyses
2. Materials and methods
Data were collected from the Quality Genetics 2.1. Location and general management of the
data bank Quality Genetics, 1998. These data herds
included farrowing records obtained from five Swed- ish nucleus herds during the period from January
The herds in this study are located in the middle 1992 until December 1998. Farrowing records from
and southern part of Sweden between latitude 55 8
each herd during the period of analyses 7 years and 60
8 north and between longitude 108 and 208 ranged from 1307 to 1604 observations. The records
P . Tummaruk et al. Livestock Production Science 68 2001 67 –77
69
consisted of herd and sow identities, sow birth date, days thereafter. If the first mating occurred within 20
boar breed, parity number, farrowing date, number of days and a repeated breeding took place within 18 to
total piglets born per litter NTB, number of piglets 100 days thereafter, Remating
5 ‘1’. born alive per litter NBA, weaning date, mating
date and mating type natural mating [NM] or 2.4. Statistical analyses
artificial insemination [AI]. Variables like lactation length LL, farrowing interval, WSI, farrowing rate
Statistical analyses were performed using SAS FR, remating rate RR and age at first farrowing
procedures SAS Institute Inc., 1989. Descriptive AFF were calculated from the primary information.
statistics were made using the MEANS and FREQ The day of weaning was defined as day 0 when
procedures of SAS for continuous and categorical calculating WSI. The sows included in the analyses
data, respectively. Analysis of variance was applied had to be born and farrowing within the same herd.
to continuous data using the General Linear Model Records of parities that did not have complete
GLM or MIXED procedures. Logistic regression information on the litter size at birth were excluded.
was applied to categorical data i.e., FR and RR Errors in reported farrowing date records were
using the GLIMMIX macro of the SAS programme. checked by constructing the frequency distribution of
Variables describing the reproductive performance the farrowing interval and only observations with
of sows, including litter size at birth NTB, NBA farrowing intervals between 140 days and 300 days
and other fertility variables WSI, FR, RR and AFF were included in the analyses; otherwise both the
were regarded as dependent variables. Factors re- previous and the succeeding farrowing data were
garded to have an influence on reproductive per- regarded as missing values. LL in the analysed data
formance were classified and included in the statisti- set was limited to 25–59 days minimum 4 weeks
cal models as independent variables. In two statisti- according to the Swedish animal welfare legislation.
cal models see below, WSI was also regarded as a WSI of sows with LL that did not fall within this
factor influencing subsequent sow reproductive per- range 3.3 of all observations as well as WSI
formance. The main factors as well as their interac- longer than 20 days 6.9 of all observations were
tions were tested for significance. Only interactions considered to be missing values. Records from parity
with a significance level of P , 0.10 remained in the
numbers above 8 were excluded 0.6 of all ob- final models. Least-squares means were obtained for
servations. Sows that had a first-farrowing age of each class of effects and combination of effects and
more than 470 days were excluded from all analyses were compared using t-tests. To account for the
6 of sows. The edited data contained observa- effect of herd management and yearly variation in
tions on 6347 litters from 2210 sows. When analys- sow reproductive performance, the effect of herds
ing litter size, crossbred litters were excluded and and effect of years nested within herd were taken
5592 purebred litters from 2171 sows were included into account for all statistical models Table 2.
in the analyses. Normal distribution of residuals from the statisti-
cal models was checked using the UNIVARIATE 2.3. Definitions
procedure option PLOT. The normality, skewness and kurtosis were measured. Since WSI had a
‘‘Farrowing’’ is a binomial trait defined as ‘0’ positively skewed distribution, a natural log trans-
when the first mating occurred within 20 days after formation was applied to the WSI data to obtain a
weaning and no farrowing took place between 106 more symmetrical distribution. After the analyses,
and 122 days after the first mating. If the first mating the results were back-transformed to obtain geomet-
occurred within 20 days after weaning and farrowing ric means of WSI in days.
took place within 106 to 122 days after the first mating, Farrowing
5 ‘1’. 2.5. Statistical models
‘‘Remating’’ is a binomial trait defined as ‘0’ when the first mating occurred within 20 days after
For each model, the number of sows, number of weaning and no remating took place from 18 to 100
observations used each analysis was based on data
70 P
. Tummaruk et al. Livestock Production Science 68 2001 67 –77
with a complete set of all variables and the sets of and LL were included in Models 4 and 5 along with
explanatory variables with significant levels based on the effects included in Models 1 and 3, respectively.
an F-test, are presented in Table 2. Parity numbers 6 Litters obtained from repeat breeding were excluded
to 8 were pooled in all statistical analyses owing to from the analyses in Model 4. Model 6 was per-
the low number of observations for each of these formed to study variation in age at first farrowing,
higher parities. Seasonal effect was regarded as the based on primiparous sows farrowing during the
effect of the month of the year when farrowing, period from January 1992 to December 1998.
weaning or mating took place. The effect of sow within herd was included in most statistical models,
except model 6, as a random effect to account for
3. Results
