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| Figure 1. Effect of lactation length (LL) on next litter size of sow, fixing the weaning to service interval to 7 days. | Figure 2. Effect of weaning to sevice interval (WSI) on next litter size of sow, fixing lactation lenght to 21 days |
| Livestock Research for Rural Development 26 (1) 2014 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
The aim of this study was to investigate the relationship between lactation length (LL), weaning to service interval (WSI) and farrowing to service interval (FSI) with the next litter size. A retrospective study was conducted using PigCHAMP® records obtained from a commercial farm in Michoacan, Mexico. Data on 36,383 litters from 6,063 pure and crossbred sows, collected from 1999 to 2008, were used. The statistical model which described the number of pigs born and number of pigs born alive per litter included the fixed effects of year of weaning, season of weaning, parity, breed group and simple interactions, plus the linear and quadratic effects of LL and WSI or FSI. Data were analyzed using the mixed procedures.
All main factors effects were significant, except breed group (p=0.09). Lactation length, WSI and FSI had significant effects on the next litter size. The equation to predict the TPB was y= 5.95 – 0.0022*LL + 0.0028*LL2 + 0.012*WSI, and for number of PBA was y= 4.77 + 0.036*LL + 0.0022*LL2 + 0.0087*WSI. The equations of the relationships of TPB and PBA with FSI were y= 6.42 + 0.0327*FSI -0.000033*FSI2 and y= 5.69 + 0.0349*FSI – 0.000036*FSI 2, respectively. Increasing LL, WSI and FSI increased the next litter size; however, it could have a negative effect on sow productivity per year and sow productive lifetime.
Key words: breed, piglets, reproductive traits, season, sows
Many factors have a direct effect on the number of pigs weaned per sow per
year in a farm, among them gestation length, lactation length (LL) or
weaning age, and weaning to service interval (WSI). Gestation length is a
very constant trait and therefore difficult to manipulate for improvement
purposes. To increase the number of pigs per sow per year it is necessary to
reduce the LL or the WSI. However, LL and WSI may affect the next litter
size. During lactation the sows are in physiological anestrous which is
rapidly reverted after weaning (Anderson 1993). Some farms use short LL in
order to maximize the economic benefits. USA farms use LL of 21 days or 14
days to get more litters per sow per year (Fahmy 1981); whereas, in Europe,
by law, LL of 28 days are used, because of improvement of reproductive
traits (Koketsu and Dial 1997) and welfare reasons; however, this practice
may decrease the number of litters per sow per year. Short lactations are
associated with a smaller litter size at the subsequent farrowing (Xue et al
1993; Dewey et al 1994; Mabry et al 1996). However, Tantasuparuk et al
(2000) reported no significant effect of LL on next litter size.
The swine herd can also be optimized by reducing the WSI. However, the relationship between WSI or weaning to conception interval and next litters size is not clear. Fahmy et al (1979) reported an increase in litter size as the weaning to estrous interval increased. Babot et al (1994) and Logar et al (1999) reported a linear effect of previous weaning to conception interval on litter size, with regression coefficients of 0.0002 and 0.0074, respectively. However, Dewey et al (1994) and Marois et al (2000) found a quadratic relationship between previous weaning to conception interval and litter size. Clark and Leman (1984) found that early weaning of pigs had no effect on next litter size of sows, when the weaning to conception interval was greater than 14 days. However, when weaning to conception interval was less than 14 days, litter size was reduced by 0.1 pigs per day between LL of 21 and 28 days. Therefore the effect of LL on litter size is likely to be influenced by WSI, and to avoid bias, previous LL and WSI should be studied together (Clark and Leman 1986). Farrowing to service interval (FSI) is a combined result of the LL and WSI of sows. Therefore it may explain the effect of both LL and WSI on next litter size.
The aim of this study was to investigate the relationship between LL, WSI and FSI with next litter size in a commercial farm in Michoacan, Mexico.
A retrospective study was conducted using PigCHAMP® records obtained from a commercial farm in Michoacan, Mexico, to test the effect of LL, WSI and FSI on next litter size of sows. Data on 36,383 litters from 6,063 crossbred (Camborough 22, F1 Landrace x Yorkshire and 1/4Landracex3/4 Yorkshire) and purebred sows (Yorkshire), collected from 1999 to 2008, were used. Sows were fed commercial diets and grouped in loose housing system, whereas lactating sows were kept separately in farrowing pens. After weaning, the sows were immediately transferred to the service/gestation units. Estrous was detected with the help of a boar 24 hours after weaning, twice a day for two hours. After estrous detection, sows were inseminated trice at 12 hours intervals. The average lactation length was 22 days.
The information obtained from the database of the herd was the animal identity, parity, farrowing date, weaning date, number of pigs per litter (TPB), number of pigs born alive per litter (PBA), lactation length, service date, weaning to service interval and sow breed.
The statistical model which described the number of pigs born and number of pigs born alive per litter included the fixed effects of year of weaning, season of weaning (spring, summer, fall and winter), parity (2, 3.. >8), breed group and simple interactions, plus the linear and quadratic effects of LL and WSI or FSI. However the final model only included the significant simple interaction and significant quadratic effects. Data were analyzed using the general mixed procedure of the SAS statistical package (SAS 2008).
All main factor effects were significant, except breed group (p=0.09). Lactation length, WSI and FSI had significant effects on next litter size (Figures 1, 2 and 3). The equation to predict the TPB was y= 5.95 – 0.0022*LL + 0.0028*LL2 + 0.012*WSI, and for number of PBA was y= 4.77 + 0.036*LL + 0.0022*LL2 + 0.0087*WSI. This means that weaning at an age of 28 days instead of 21 will increase litter size in 1.0 pig born alive and reduce it by 0.7 pigs, if the age of weaning was 15 days (keeping WSI at a constant age of 7 days). However, increasing the WSI from 7 to 14 or 28 days (keeping LL constant to 21 days) would increase litter size in only 0.08 and 0.24 pigs born alive, respectively.
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| Figure 1. Effect of lactation length (LL) on next litter size of sow, fixing the weaning to service interval to 7 days. | Figure 2. Effect of weaning to sevice interval (WSI) on next litter size of sow, fixing lactation lenght to 21 days |
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| Figure 3. Effect of farrowing to service interval (FSI) on next litter size of sow. |
The equations of the relationships of TPB and PBA with FSI were y= 6.42 + 0.0327*FSI -0.000033*FSI2 and y= 5.69 + 0.0349 – 0.000036, respectively.
The increase of the number of pigs born alive in the next litter as LL increases, found in this study, agrees with the result of Xue et al (1993; 1997) who showed that longer LL was associated with higher litter size, shorter weaning to estrous interval, longer farrowing to service interval and longer farrowing interval. Mabry et al (1996) in the United States also reported an increase in the PBA as LL increases. They mentioned that an increase in LL of 15 to 20 days or from 10 to 15 days would result in an average litter size increase of 0.20 pigs in the sow’s next litter. These values are smaller than the predicted values, in this study, of 0.6 and 0.45 pigs, for the same intervals, respectively. Babot et al (1994) reported increases of litter size from 0.03 to 0.04 pigs born alive for each day of previous LL, which agree with the value of 0.036, found in this study. Xue et al (1997) reported coefficients of 0.07 and 0.05 for LL with TPB and PBA. However, increasing LL would increase farrowing interval, decrease pig weaned per farrowing per year and could reduce breeding herd productivity (King et al 1998).
Weaning to service interval
An increase of size in the following litter with increase in the weaning to estrus interval was found in crossbred sows by Fahmy et al (1979) in Canada, Tantasuparuk et al (2000) in Thailand, and Cavalcante-Neto et al (2008) in Brazil, which agrees with the results of this study. However, Kemp and Soede (1996) reported a negative correlation between WSI (varying from 4 to 9 days) and the next litter size. As mentioned by Tantasuparuk et al (2000), the reason for the increase in litter size with longer WSI might be that sows had a longer period to recover from a catabolic stage around weaning. Further analysis of our data including WSI less or equal than 16 days as Carregaro et al (2006) did, showed no significant relationship with the next litter size. However, including data up to 28 days showed a significant linear relationship of WSI with PBA (Results not shown). When WSI data were grouped into three categories: <5 and from 5 to 10 days and from 11 to 45 days, as Karveliene et al (2008) did in Lithuania, the PBA means were 8.58, 8.37 and 8.67 (p<0.01) indicating a quadratic relationship. However, Karveliene et al (2008) reported a negative relationship. Therefore, results between studies may vary depending in farm management differences but also in the lengths of WSI data used, and in the treatment of WSI as a quantitative or categorical variable. Nevertheless, body condition after weaning may play an important role in return to estrous and without a detrimental effect on the size of the next litter. WSI in a herd could be reduced through better management practices and by genetic means, although their heritability is low (Marois et al 2000; Cavalcante-Neto et al 2008).
We could not find in the literature reports of the effect of FSI on litter size. However, our results showed an increase of litter size as FSI increased. In part this was expected because LL and WSI, the two components of FSI, increased litter size as well.
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Received 12 December 2013; Accepted 22 December 2013; Published 1 January 2014