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
repeated observations for many of the sows. Model 1 was used to analyse the variation in litter size at birth
3.1. Descriptive statistics for reproductive obtained from purebred matings, based on farrow-
performance ings from January 1992 until December 1998. Using
Model 2, variation in WSI was analysed based on Descriptive statistics based on edited data for the
weaning records obtained from July 1992 until June reproductive performance of Hampshire sows, in-
1998. Weaning years were classified into six groups, cluding the number of non-missing values, arithmetic
each representing a 12-month period Jul 92–Jun means, standard deviations and ranges of the data,
93, Jul 93–Jun 94 and so on. LL was classified into are presented in Table 1. The percentage ratio of
three groups based on the number of observations in litters obtained through NM vs. litters obtained
each group 25–38, 39–45 and 46–59 days. Model through AI NM: AI was 85:15 for primiparous
3 focused on factors influencing FR and RR for sows sows gilt matings and 36:64 for multiparous sows.
mated during the period from July 1992 until June However, NM was used less frequently than AI for
1998. LL and mating years were classified in the the sows being mated for the first time after weaning
same way as in Model 2. In Models 4 and 5, effects 13:87. The proportion of AI used at first mating
of WSI and LL on subsequent reproductive per- after weaning varied among the herds, ranging from
formance were studied. WSI was classified into six 79 to 94. Furthermore, the proportion of sows
groups according to the number of observations and being mated by NM or AI depended upon WSI. For
the general means of litter size in each group 0–3, WSI
7 days, a lower proportion of sows were 4, 5, 6, 7–9, 10–12 and 13–20 days. Effects of WSI
mated by NM than by AI 5 vs. 95, whereas for
Table 1 Descriptive statistics for some reproductive traits of Hampshire sows from five nucleus herds in Sweden during the period from 1992 to
1998 Parameter
N Mean
S.D. Range
Parity all litters 6347
2.8 1.8
1–8 Parity purebred litters
5592 2.6
1.7 1–8
Age at first farrowing days 1873
385.9 34.2
293–470 Total born litter
5592 9.8
2.9 1–21
Live born litter 5592
9.0 2.7
0–19
a
Lactation length days 5191
41.0 6.2
25–59
a,d
WSI days 3923
5.0 2.4
0–20 Farrowing interval days
3738 173.4
23.0 145–298
b,d c
Farrowing rate 3922
68.3 –
53.3–83.1
b,d c
Remating rate 3922
22.0 –
11.5–34.2
a
Based on sows weaned between July 1992 and June 1998 6-year period.
b
Based on sows mated between July 1992 and June 1998 6-year period.
c
Variation among herds. Based on a weaning-to-first service interval WSI of
20 days.
P . Tummaruk et al. Livestock Production Science 68 2001 67 –77
71
a longer WSI 8–20 days, a higher proportion of Primiparous sows had a longer P
, 0.01 WSI than sows were mated by NM than by AI 67 vs. 33.
sows in parities 3, 4, 5 and 6–8. Additionally, NM was used mostly for the repeat
Fertility of the sows, as indicated by FR and RR, breedings 79.5. Due to these extreme imbalances,
was influenced P , 0.001 by parity number Table
mating type was excluded from the statistical 2. Primiparous sows had the highest RR 25.4-
models. units and the lowest FR 63.7-units. A decrease
Frequency analysis revealed that the proportion of in RR as well as an increase in FR was observed as
sows remated within the period 18 to 100 days after parity number increased Table 3.
first service was 22 Table 1. Of those remating, the proportions of repeat breedings within 18–24,
3.3. Effect of season 25–37, 38–45 and 46–100 days after first service
were 47, 14, 17 and 22, respectively. Across parity, no seasonal variation in litter size at
In Table 2, the structure of the analysed data and birth was found Table 2. However, the interaction
the levels of significance for all factors included in between parity and season was significant for both
the statistical models are presented. NTB P
, 0.001 and NBA P , 0.05; Table 2. Primiparous sows were less influenced by season
3.2. Effect of parity than multiparous ones; for instance, litter sizes NTB
and NBA decreased when farrowing occurred in Parity number influenced litter size at birth P
, November for sows in parities 2 to 4 and in October
0.001 and WSI P , 0.01. Both NTB and NBA
for sows in parities 5 to 8 but these events were not increased as parity number increased from 1 to 5,
observed for parity 1 sows. where the maximum litter size was observed Table
Season influenced P , 0.001 WSI Table 2. The
3. The WSI was longest in primiparous sows and longest WSI was observed for sows weaned in
decreased as parity number increased Table 3. January, August and September Table 4. Further-
Table 2 Structure of the analysed data and levels of significance for factors included in the models significance levels for each factor are indicated
using a P-value based on the F-test Data analyses
Model 1 Model 2,
Model 3 Model 4
Model 5 Model 6,
NTB NBA
WSI FR
RR SNTB
SNBA SFR
SRR AFF
Period of analysis yr 7
7 6
6 6
6 6
6 6
7 No. of observations
5592 5592
3923 3922
3922 2199
2199 3922
3922 1873
No. of sows 2171
2171 1544
1542 1542
1158 1158
1542 1542
1873 Statistical methods used
MIXED MIXED
GLIMMIX MIXED
GLIMMIX GLM
Explanatory variables Parity
0.001 0.001
0.002 0.001
0.001 0.001
0.001 0.001
0.001 –
Herd 0.001
0.001 0.001
0.001 0.001
0.039 0.121
0.001 0.001
0.001 Year herd
0.101 0.011
0.001 0.001
0.001 0.073
0.014 0.001
0.001 0.001
Season 0.426
0.159 0.001
0.001 0.057
0.341 0.068
0.001 0.086
0.001 Lactation length
– –
0.001 0.098
0.353 0.622
0.291 0.094
0.379 –
WSI –
– –
– –
0.059 0.195
0.001 0.001
– Parity
3 Season 0.001
0.050 NS
NS NS
NS NS
NS NS
– Parity
3 Lactation length –
– 0.072
NS NS
NS NS
NS NS
– Lactation length
3 Season –
– 0.001
0.012 0.001
NS NS
0.011 0.001
– NTB
5 Number of total piglets born per litter; NBA 5 number of piglets born alive per litter; WSI 5 weaning-to-first-service interval; FR
5 farrowing rate; RR 5 remating rate; SNTB 5 subsequent number of total piglets born per litter; SNBA 5 subsequent number of piglets born alive per litter; SFR
5 subsequent farrowing rate; SRR 5 subsequent remating rate; AFF 5 age at first farrowing. ‘NS’ denote factors that have been tested but were excluded from the final model due to leaving a P value of
. 0.10. ‘–’ denote factors that have not been tested since they have not been regarded as important for the traits analysed.
72 P
. Tummaruk et al. Livestock Production Science 68 2001 67 –77 Table 3
Effect of parity number on reproductive performance least-squares means Parity
Model 1 Model 2
Model 3 N
NTB NBA
N WSI
N FR
RR
a a
a a
a
1 1872
8.8 8.1
1262 4.9
1261 63.7
25.4
b b
ab b
b
2 1438
9.4 8.8
902 4.8
902 69.5
19.0
c c
bc c
b
3 892
10.3 9.5
671 4.7
671 74.1
17.2
d cd
c bc
bc
4 587
10.7 9.7
474 4.7
474 70.0
15.5
e d
bc bc
cd
5 382
11.2 10.0
310 4.7
310 72.0
12.4
e cd
c c
d
6–8 421
11.2 9.7
304 4.6
304 76.3
10.0
abcd
Means with a common superscript are not different P . 0.05. NTB 5 Number of total piglets born per litter; NBA 5 number of
piglets born alive per litter; WSI 5 weaning-to-first service interval; FR 5 farrowing rate; RR 5 remating rate.
more, the interaction P , 0.001 between LL and
LL of 4–5 and 6 weeks. However, for sows with a season for WSI revealed that the seasonal effect on
LL of 7–8 weeks, the lowest FR was observed in WSI was more pronounced in sows with a LL of 4–5
sows mated in March. or 7–8 weeks compared with an intermediate LL 6
A seasonal variation in age at first farrowing was weeks; Fig. 1.
also found Table 2. Sows farrowing in August and Seasonal influence was also found for both FR and
September were younger P , 0.05 than those far-
RR Table 2. The lowest FR and the highest RR rowing during the period from October until January
were found for sows mated in August and September Table 4. A difference in AFF of more than 7 days
Table 4. The interaction between LL and season was significant.
was also significant for both FR P , 0.05 and RR
P , 0.001. Fig. 1 shows the seasonal variation in
3.4. Effect of lactation length FR. The pattern varied depending on the length of
lactation. A decrease in FR was observed in sows The effects of LL on subsequent litter size as well
mated during August and September for sows with a as on subsequent FR and RR were not significant
P . 0.05; Table 2. However, LL influenced P ,
0.001 WSI Table 2. Across parity, weaning at
Table 4
4–5, 6 and 7–8 weeks resulted in an average WSI of
Seasonal variation in some reproductive traits least-squares means
5.0, 4.7 and 4.6 days, respectively. Differences
e
between least-square means 0.3 day were signifi-
Month WSI
FR RR
AFF
cant P , 0.001. In this data, about half of the litters
days -units
-units days
a bcd
b a
were weaned at 6 weeks of age 46 and the
January 5.0
71.8 14.4
392.6
bc c
c ab
proportions of litters weaned between 4 and 5 and 7
February 4.6
77.7 13.0
388.8
c bcd
b abc
March 4.5
71.3 15.0
385.8
and 8 weeks were 32 and 23, respectively.
bc bc
c bc
April 4.7
75.5 13.2
382.9
bc c
b ab
May 4.7
76.3 15.1
389.2
3.5. Effect of WSI on subsequent reproductive
bc bd
abc bc
June 4.6
70.3 17.1
384.5
ab bc
abc bc
performance
July 4.8
74.7 16.1
384.7
a a
a c
August 5.0
62.5 20.7
379.3
a a
ab c
September 4.9
63.3 19.5
382.1
A WSI between 7 to 9 days was followed by a
ab ad
ab a
October 4.7
65.2 18.5
389.5
lower P , 0.05 subsequent litter size NTB and
bc ab
abc a
November 4.7
68.5 17.1
391.8
NBA compared with a WSI of 4 days or 13–20 days
bc bc
bc a
December 4.7
73.0 14.1
394.4
Fig. 2.
abcd
Means with a common superscript are not different P .
WSI also influenced P , 0.001 subsequent FR
0.05.
and RR Table 2. Sows with a WSI of 6 days had
e
Weaning month for weaning-to-first service interval WSI,
the lowest FR and the highest RR, which differed
mating month for farrowing rate FR and remating rate RR, and
P , 0.05 from sows with a WSI of 0 to 5 or 10 to
farrowing month for age at first mating AFF.
P . Tummaruk et al. Livestock Production Science 68 2001 67 –77
73
Fig. 1. Seasonal variation in weaning-to-first service interval WSI and farrowing rate by lactation length.
abcd
Fig. 2. Effect of weaning-to-first service interval WSI on subsequent litter size. Means with a common letter within line are not
different P . 0.05.
74 P
. Tummaruk et al. Livestock Production Science 68 2001 67 –77
abcd
Fig. 3. Effect of weaning-to-first service interval WSI on subsequent farrowing rate and remating rate. Means with a common letter
within line are not different P . 0.05.
20 days. Moreover, a WSI of 5 days resulted in a studies have shown that the selection for high
lower P , 0.001 FR and higher RR compared with
production might result in undesirable side-effects a WSI of 4 days Fig. 3.
for reproductive traits reviewed by Rauw et al., 1998. The selection history, as such, may be one
reason for the lower reproductive performance of the
4. Discussion Hampshire compared with the Landrace or Yorkshire
