Classification of Sows for Longevity Based on Total Number of Piglets Born Alive in the First Parities

Abstract

The aim of this study was to classify the sows for longevity based on the total number of piglets born alive in the first parities. Data comprising the period from January 2017 to March 2020 were obtained from a commercial farm with 5,500 sows. A total of 8,869 sows were used in the analyses. The animals were divided into three parity groups according to the 1st and 3rd quartiles of the total number of piglets born alive in the first and second farrowing: parity 1 - 1L (low): <12 piglets, 1M (medium): 12 to 16 piglets, and 1H (high): >16 piglets; parity 2 - 2L: <12 piglets; 2M: 12 to 16 piglets, and 2H: >16 piglets. Sows exhibiting high performance in the first parity continued to do so up to the sixth parity. Regarding parity 1 classification, 1H sows (>16 piglets) produced more piglets than the other classes up to the fifth parity. When the parity 2 classification was added, 1H2H and 1H2M sows produced more piglets up to the fourth parity. Comparison of the length of stay of sows in the herd showed a longer mean stay of the 1H2M class. The main reasons for culling were cystitis, uterine prolapse, hoof problems, and physical condition. In general, the results demonstrated that it is possible to use the number of piglets born alive in the first two parities of sows to predict the productivity of subsequent parities. The method is able may therefore help to maintenance of the sow in the herd or culling of sows.

Keywords:
productivity; sows; subsequent performance

HIGHLIGHTS

Data from the first two farrowings are sufficient to predict subsequent productivity.

Productive performance of sows can be to predict using the total number of piglets born alive.

Causes of culling sows is cystitis, hulls and physical condition in HML to first parity order.

INTRODUCTION

In recent years, the main objectives of pig production have been to increase the number of piglets born in each litter, in addition to improving the efficiency of the production system [¹]. Within this context, the selection of hyperprolific sows has led to a substantial increase in piglet production [²]. Therefore, the selection worked, the aging sow becomes more susceptible to environmental variations that influence its performance, unlike younger sows that can better express their potential.

Several authors have shown that it is possible to associate litter size at born of young sows with longevity [³,⁴] and a relationship between high productivity and retention of sows in the herd [⁵]. Moreover, to evaluate genetic and phenotypic correlations of number of piglets born as an indicator of longevity [⁶]. Other authors used classifications based on the total number of piglets born alive in the first two parities as indicators [³,⁴,⁷,⁸]. Furthermore, there is strong evidence that sows maintain the same production levels of piglets throughout life [⁹], i.e., sows with high productive potential remain highly productive until the end of life, while sows with low potential are poorly productive.

Thus, using the total number of piglets born alive as a method to selection or culling of sows may have benefits for the farm, especially economic ones. Therefore, the objectives of this study were to develop classifications for sows until parity 6 based on the number of piglets born alive in the first two parties and to evaluate the relationship between productivity of the different classes.

MATERIAL AND METHODS

Farm characterization

This research approach does not require institutional ethics committee approval. Data were obtained from a piglet production unit (PPU) in the town of Carambeí, Paraná, Brazil, Latitude 24º 55' 04" S. Longitude 50º 05' 50" W. This unit possesses a housing capacity of 5,500 sows and is equipped with a biosecurity system and an electronic system for the control of temperature (18-20^oC) and ventilation (evaporative cooling and exhaust fans) in all pens. The maternity unit has a heated floor for piglets and the PPU produces its own replacement sows. Camborough and AG 1020 (Agroceres PIC^®) were the genetic lines used.

In interval between estrus and weaning or when introduced into the herd, sows pass through the breeding sector for artificial insemination. In this sector, the animals are housed in cages containing a drinker and an individual feeder. After artificial insemination, a batch is formed and transfer to the gestation sector. All gestation pens are equipped with drinkers and electronic feeders (electronic sow feeding). This sector is divided into static pens so that none of the sows enters the pen after batch formation. In abortion cases, the sow is removed of the pen. One week before the expected farrowing date, the sows are transferred to farrowing rooms. All rooms are equipped with adjustable metal farrowing crates, slatted flooring, and a manual drinker and feeder, as well as a heating system, drinkers, and feeders for the piglets. The sows remain in the farrowing rooms until weaning, which on average occurs 21 days after farrowing, and are then returned to the breeding sector to be inseminated again. In all production sectors, data are collected by the employees using forms. These data are then sent to the office and entered the Agriness S2^® farm management software. With the database being updated daily, the software can generate information, spreadsheets, graphs, and other important reports for the analysis of farm productivity.

Data collection

To compile the database, individual data was collected for each sow: reproduction- identification and body condition of the sow (caliper range), responsible employee, and number of artificial inseminations, as well as time and date of insemination; gestation - interval between estrus and weaning, abortion, and pen transfers; farrowing and lactation - identification of the sow, parity order, days of gestation, date and time of farrowing, type of farrowing (dystocia, induced, normal, preterm, or preterm and dystocia), farrowing duration, total number of piglets born alive, number of stillborn piglets, number of mummified piglets, total number of piglets weaned and of dead piglets at weaning, and mean piglet weight at birth and weaning. Information causes of sow culling and mortality was also compiled.

Data were exported to electronic spreadsheets in which each line represented one sow, and the columns corresponded to the productive variables. The database used included data collected from January 2017 to March 2020. Database not presented but available from the authors.

Definitions

Return to estrus was defined when sows, after insemination and transfer to the gestation pens, were inseminated again within an interval shorter than the gestation period [⁷]. In this case, only data of inseminations that resulted in birth were considered for analysis. In view of its capacity and requirements, the PPU uses so-called nurse sows, i.e., sows that have weaned their own piglets but continue their lactation to nurse piglets from other litters (adoptive litters), which is possible cause of the ratio between the number of piglets born and available teats in the sow at farrowing. In this case, the results from adoptive litters of nurse sows were not considered in the database or analyses.

The weaning-to-service interval was defined as the number of days after weaning to first insemination. The number of non-productive days was defined as days when the sow was neither gestating nor nursing [⁸]. The number of dead piglets at farrowing or until weaning was calculated as follows: (dead piglets = number of dead piglets/number of live or weaned piglets + number of dead piglets).

Sows with a gestation duration of 100 to 122 days, at least 1 piglet born alive, and lactation of 10 to 41 days. Divergent information outside these criteria, as well as typing errors, were eliminated from the database.

Statistical analysis

The data were exported from AGRINESS S2^® to electronic spreadsheets and then entered the R 3.3.0 package (RStudio Team, 2020) for statistical analysis. Coherence of the data was evaluated using descriptive statistics and graphs.

Groups to test the possibility of classifying the most productive sows based on data from the first two parities). The sows were defined by quartiles (Q1, IQR and Q3) of the number of piglets born alive in the first two months. The classification was: Low (L) for sows with <12 piglets born alive, Medium (M) for sows with 12 to 16 piglets born alive and High (H) for sows with >16 piglets born alive, as described by [³, ⁸].For 1^st parity, the mean number of piglets born alive was 17.13 for 1H, 13.66 for 1M, and 8.63 for 1L, with a percentage of sows in each group of 29.0% (1H), 36.31% (1M), and 40.0% (1L). For 2^nd parity, the mean number of piglets born alive was 17.24 for 2H, 13.62 for 2M, and 8.11 for 2L, with a percentage of sows in each group of 26.5% (2H), 44.5% (2M), and 28.8% (2L). In view of the high renewal rate (close to 45% of the breeding stock per year), females until parity 6 were considered for data analysis. It is important to highlight that the amount of available information decreases with increasing parity order, with a consequent increase in the variance of the results. Females with > 7 parity order (representing 4% of total population data) were discarded due to a lack of information and a wide range of results. This fact permitted classification of sows until parity 6 in this analysis. The groups were tested by fixed model ANOVA with multiple comparisons by the Tukey test at a level of significance of 5%. As describe below:

${\gamma }_{ij}=\mu +{\alpha }_i+{\epsilon }_{ij}$ (1)

Y_ij = response of each observation in determined classification;

µ = overall mean of all classifications;

α_i = effect of HML classification;

ɛ_ij = aleatory error.

RESULTS

The number of piglets born alive was higher in the 1H group (>16 piglets) compared to the other groups (P<0.05) up to the fifth parity when there was no longer a difference between means (Figure 1a). Likewise, the born alive HML classification was used to evaluate sows considering weaned piglets (Figure 1b). In parity 1, sows classified as 1H (>16 piglets) had a larger number of weaned piglets than the other groups (P<0.05). However, by parity 3, weaned piglets was no longer a difference between groups. In parity 6, the 1L group (<12 piglets) exhibited the smallest number of weaned piglets (P<0.05), while the 1H and 1M groups were similar (P>0.05).

Figure 1
Total born alive in relation to sows parity order based on classification of litter size of first parity order (1L: <12 piglets, 1M: 12 e 16 e 1H: >16 piglets (a); Weaned piglets in relation to sows parity order based on classification of litter size of first parity order (b). Significant differences by LSD test at P<0.05 indicated by letters.

By adding parity 2 sows to the HML classification, the most productive sows were classified as 1H2H and 1M2H (Figure 2 a-c). Sows exhibiting high productivity in the first two parities tended to remain highly productive up to the sixth parity. However, when the sows were classified as 1L2M and 1L2L, they obtained increasing productivity between the third and sixth parity and reached higher mean values than sows classified as 1L2H.

Figure 2
Total born alive in relation to sows parity order based on classification of litter size of first and second parity order. a) Sows classified as high (H) in first farrowing (>16 piglets born alive) and interactions with second farrowing class (2H: >16 piglets, 2M: between 12 e 16, 2L: <12 piglets). b) Sows classified as medium (M) in first farrowing (between 12 e 16 piglets born alive) and interactions with second farrowing class. c) Sows classified as low (L) in first farrowing (<12 piglets born alive) and interactions with second farrowing class. Significant differences by LSD test at P<0.05 indicated by letters.

The mean length of stay of sows in the herd was 2.74 farrowings (Figure 3). Sows classified as 1H2M (3.25 farrowings) and 1M2H (3.23 farrowings) stayed longer in the herd (P<0.05) than the other groups. Furthermore, 1H2H sows stayed on average 0.14 farrowings less than 1H2M sows (P<0.05). The shortest longevity was observed for sows classified as 1L2L (2.93 farrowings).

Figure 3
Interaction between productive performance of first and second parities in relation of sows longevity (cycles). Classification of litter size HML - Parity Order 1st PO (1H: >16 piglets, 1M: between 12 and 16, 1L: <12 piglets) e 2nd PO 2 (2H: >16 piglets, 2M: between 12 and 16, 2L: <12 piglets). Significant differences by Tukey test at P<0.05 indicated by letters.

Unplanned culling was the main reason for sow removal (Table 1). Cystitis was the most common cause of culling among sows classified as 1H in the first parity (20.1%), followed by a low genetic index (14.8%) and uterine prolapse (14.4%). Culling due to problems in the locomotor system (legs and hoof), in addition to physical condition, were the main reason for removal of sows classified as 1M. In the group of sows classified as 1L, the main reasons were hoof problems (30%), physical condition (16.2%), and return to estrus (11.6%). Advanced age did not account for more than 1% of culling causes per group.

Table 1
Causes of culling sows (%) according to classification HML to first parity order

		Classification
Removal causes, %	1H	1M	1L
N	507	1109	580
Abortion	4.3	3.6	2.8
Anestrus	13.8	0.1	10.7
Straightness	6.5	13.3	4.8
Low productivity	4.7	4.8	5.5
Low genetic index*	14.8	4.9	0.2
Hulls	0.4	20.5	30.0
Cystitis	20.1	0.4	0.3
Physical condition	0.2	16.7	16.2
Depopulation	11.4	0.2	0.5
False pregnancy	0.2	13.5	8.8
Advanced age	0.2	1.0	0.7
Ileitis	0.2	0.2	0.2
Metritis	4.5	4.8	0.2
Metritis, Mastitis, Agalactia	0.4	0.6	3.8
Farrowing problems	3.0	2.4	1.2
Rectal prolapse	0.8	2.4	1.9
Uterine prolapse	14.4	10.6	0.3
Return to estrus	-	0.2	11.6
Ulcer/anemic	-	-	0.3

• Classification of litter size HML - Parity Order 1st PO (1H: >16 piglets, 1M: between 12 and 16, 1L: <12 piglets) e 2nd PO 2 (2H: >16 piglets, 2M: between 12 and 16, 2L: <12 piglets). *Genetic index: based on genealogical information (mother and grandmother), production indices and weaning to estrus interval

DISCUSSION

Data show that sows with a large total number born alive in the first and second parity tend to remain highly productive up to the sixth parity, in agreement with other studies [³,⁴,⁵,⁷,⁸]. Litter size is determined by the sow’s genetic potential, animals with large litters in the first and second parity are expected to have large subsequent litters [⁷]. Moreover, a high genetic potential for litter size may imply that these sows have an advantage in reproductive physiology, i.e. high uterine capacity, but it may also imply that these sows are better able to withstand environmental factors, i.e. climate condition or nutritional state, affecting physiological factors. Evidence of this are the genetic correlations between first-parity litter size and litter size in subsequent parities, observed in literature r = 0.84 [¹⁰] and r = 0.88 [¹¹]. However, these authors highlighted that, despite the high genetic correlations, the phenotypic correlations between parities are low, demonstrating a considerable environmental effect on litter size.

There was a difference between sows classified as 1L2L and 1H2H. On average, 1L2L sows produced 2.05 less piglets per farrowing than 1H2H sows. However, if productive life (3-10 parities) is considered, this difference can reach 21 piglets less per female in the herd [³]. Litter size in the third parity and higher decreased with decreasing first- and second-parity litter size, although independently, no interaction was observed. However, a dependence between first- and second-parity litter-size, if the litter is large in the first parity, the effects of classification of the second parity are less pronounced [⁷].

Supporting these results, a low-productive sows stay in the herd for a shorter period (Figure 3). The main factor responsible is the low economic return of low-productive sows, which results in early culling. Sows classified as 1H2M (3.25 farrowings) and 1M2H (3.23 farrowings) stayed longer in the herd (P<0.05) than the other groups. Sows with average litters of 12 to 14 piglets stay in the herd for a longer period [¹]. Although large litters are desired, they can have consequences for the productive life of sows. Large litters can reduce the sow’s lifespan, increase the probability of unplanned culling, and the risk of bodily injury and can have a negative impact on sow welfare during gestation, farrowing, and lactation [¹,¹²]. However, specialized management for this nutritional and body demand of the sows is always a priority on the farm. In addition, adequate facilities, thermal comfort and management that meet the well-being of the sows are necessary. Furthermore, an increase in litter size leads to piglets with uneven weight by reducing the average weight of the total number of piglets born and born alive [¹³]. This fact increases the need for handling and caring for the piglets, especially when the number of functional teats is lower than the total number of piglets born alive [²]. In addition, large litters can increase farrowing duration and consequently the number of stillborn piglets [¹⁴]. Finally, from an economic point of view, three farrowings of a sow are necessary to recover investments [¹⁵]. Therefore, the longer the sow stays in the herd, the greater the chances of recovering all investments made It is therefore important to identify sows with a high potential early and to maintain them in the herd since the return on their investment occurs sooner, improving the profit margins of pig farming [³].

In the present study, the average longevity in the herd was 2.7 farrowings. In general, the average number of farrowings is relatively low on commercial farms, ranging from 3 to 4 [¹⁶]. Additionally, maintaining a stable age structure in the herd provides a higher percentage of more productive sows (OP3 to OP5). However, the farm of the present study has an attached sector to produce replacement sows. This fact may have influenced selection and renewal of sows and culling because of the high availability and lower cost (compared to external acquisition) of replacing sows, with the removal of sows due to old age accounting for no more than 1% of all cullings in each HML class. We found reproductive failures to be the most common reasons for unplanned sow removal on the farm, including cystitis, uterine prolapse, and anestrus. Infections in the genitourinary system can cause reproductive disorders, with the existence of a clear association between anestrus, endometritis, and a high degree of cystitis [¹⁷]. Prolapses are more common in sows with >PO3, with litters of less than 11 piglets, occurrence of re-service in matting, gestations of less than 113 days and occurrence in summer, autumn and winter [¹⁸].

Sows classified as 1M and 1L are discarded due to hoof and physical condition problems. Hoof problems and physical condition are the main reasons for culling sows classified as medium and low productivity and can be associated with the housing system [¹⁹]. Lameness indirectly affects farm productivity through its effect on sow longevity, whereas claw lesions directly affect some reproductive parameters. Culling due to physical condition includes bodily injuries (bites, bruises, skin lesions) caused by social interactions and low body condition scores [²⁰]. Hoof problems are the results of injuries, infections, or malformations However, with growing severity of the injuries, the condition can progress, leading to lameness and compromising animal welfare [²¹]. Lameness may also reduce general activity, social behavior and exploration, as reviewed by Weary and coauthors [²²]. The sows of this study were housed in static collective pens, which are designed to improve animal welfare and to encourage the natural behaviors of sows, including social interaction. However, fights and agonistic interactions are inevitable, especially for hierarchy formation and competition for food, resulting in skin and hoof injuries, lameness, vulva biting, and return to estrus [²³]. This scenario directly and indirectly affects economic viability and productive and reproductive performance, which may compromise litter performance and increase mortality and early culling rates of sows [²⁴].

Some limitations related to the analysis and interpretation of the present results must be mentioned. Data were obtained from a single commercial farm. In addition, nutritional, genetic, or environmental data were not included in the analyses. However, this study shows that it is possible to predict the productivity of sows assigned to classes based on the total number of piglets born alive in the first two parities, in which highly productive sows tend to maintain high productivity, while low productive sows remain unproductive across farrowings. This fact permits to select sows that are more productive or that have a greater chance of remaining on the farm; particularly, it is possible to save time with selection, accelerating the productivity gain of the farm. From an economic point of view, this is also advantageous since sow costs are diluted with increasing parity. In addition, investments are allocated to sows that provide financial return as a result of the increase in the number of piglets produced, thus contributing to improving the economic results of the farm.

CONCLUSION

The combination of production data from the first two parties can efficiently predict to maintenance of the sow in the herd or culling sow. The method can identify the productive performance of superior and inferior sows, contributing to decision-making on selection or culling.

Acknowledgments

We acknowledge the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), the Fundação Araucária, and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for grants awarded.

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• Funding:
  This research was funded by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), grant number 455991/2014-6.

Edited by

• Editor-in-Chief:
  Paulo Vitor Farago

• Associate Editor:
  Paulo Vitor Farago

Publication Dates

• Publication in this collection
  08 Nov 2024
• Date of issue
  2024

History

• Received
  03 July 2024
• Accepted
  26 Aug 2024