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Effects of birth weight, parity and litter size on pig performance, health and welfare

The animals that were retained several times throughout the flow originated from sows with lower average parity. They had a much lower carcass weight (around 10kg) and a higher average score for lameness, pleurisy and enzootic pneumonia lesions.

Good sow and piglet management is crucial to maximize profit and needs to be adapted to each farm depending on factors such as genetics or health status. Information from the farrowing rooms is key to improve management. What are the main factors to consider? In the following study, all 1050 pigs from a single batch born during one week in a farrow-to-finish farm were tagged and weighed at birth and followed through the production cycle up to slaughterhouse. We discuss the effect of birth weight, parity of the sow and litter size on pig performance, health and welfare at different stages.


Relationships between parity, litter size and birth weight

The parity of the sow (1 to 6) did not affect the birth weight of the offspring (1.34 ± 0.32kg) but gilts had smaller litters than multiparous sows (10.9 vs. 13.0 piglets born alive). As litter size increased, birth weight decreased and percentage of animals with birth weight <1kg increased (table 1). Larger litters were also heavier (total litter weight) with no apparent limit to the weight of the litter.


Table 1. Weights of piglets and litters depending on the number of piglets born alive per litter.

Piglet born alive → 8 9 10 11 12 13 14 15 16 17 19
Average piglet weight, kg 1.64 1.65 1.65 1.45 1.36 1.31 1.25 1.25 1.25 1.20 1.18
Average litter weight, kg 13.2 14.8 16.5 16.1 16.5 16.8 17.4 19.0 19.9 20.4 22.9
% of piglets <1kg 0 0 0 9 13 15 21 13 18 29 31
% of piglets <1.3kg 13 12 10 27 41 46 55 53 55 59 52


Effects of parity and litter size on performance

Pigs born to gilts had lower growth during lactation and were 2 kg lighter when transferred to the finishing unit at 60kg than those born to multiparous sows. Nevertheless, pigs born to gilts were able to catch up to pigs born to multiparous sows during the finishing period and all animals were slaughtered at similar weights. However, pigs born to gilts had higher mortality rate during the productive cycle, especially during lactation (18.5% vs. 9.1%), and double the lameness prevalence (21% vs. 11%) prior to slaughter. Litter size had no effect on any of the variables studied despite its initial relationship with birth weight.


Birth weight, the main factor affecting performance

Pigs were divided into four groups depending on birth weight: <1kg, from 1 to 1.3 kg, from 1.3 to 1.7 kg and >1.7 kg. The four groups are described in table 2. The average parity of the four groups was similar. However, litter size decreased from 14.0 piglets to 11.2 piglets as the birth weight increased. The initial difference in the average weight of the animals in groups <1 and >1.7 kg at birth was around 1kg and it became a 21 kg difference at slaughter. When calculated by regression, 100g of a difference in birth weight became 1.3 kg of a difference in carcass weight.

Table 2. Evolution of the weight of the pigs depending on the birth weight group.

Birth weight group → <1kg 1-1.3kg 1.3-1.7kg >1.7kg
Number of pigs in the group 149 299 459 136
Average parity 3.4 3.3 3.4 3.3
Average born alive 14.0 13.7 12.9 11.2
Average birth weight, g 823 1157 1479 1844
Coefficient of variation, % 15 7 8 7
Average weight weaning, kg 5.4 6.5 7.5 8.3
Coefficient of variation, % 29 23 19 18
Average slaughter weight, kg 103 113 118 124
Coefficient of variation, % 13 11 13 12

The variability of weights in the lighter groups was also higher compared with the heavier groups making the management of these animals more complicated. However, this variability was similar among the four groups at slaughter. Mortality was also clearly affected by the birth weight group. Animals with birth weight <1kg had a 30% mortality with most of it occurring during the lactation period (figure 1).

Figure 1. Mortality in each birth weight group by stage of production.
Figure 1. Mortality in each birth weight group by stage of production.

At slaughter, lungs were scored for pleurisy (SPES) and enzootic pneumonia (EP) like lesions (adapted from British Pig Health Scheme) and heart and liver condemnations were recorded (table 3). Pleurisy and EP scores were higher for animals with low birth weight as shown in the table.

Table 3. Prevalence of lesions in slaughterhouse for each group of birth weight.

Pathology in slaughterhouse <1kg 1-1.3kg 1.3-1.7kg >1.7kg
Pleurisy, SPES 0.60 0.60 0.48 0.42
Enzootic Pneumonia score 1.85 1.38 1.50 1.55
Heart condemnations, % 7 12 8 9
Liver condemnations, % 1 1 1 3

The strategy followed by the farmer of increasing the size of his litters was questioned at this stage and his attention was brought to the fact that he needed to pay more attention to the amount of small animals and their management.


Pig flows within the farm

In this study, the staffs were allowed to do the usual management and the tagged pigs were tracked through the cycle. Despite the farmer claimed the farm followed an all-in/all-out system, it was not well applied. This is a common situation in many farms to keep pig groups homogeneous. Three different flows of pigs were identified:

  • Pigs that followed the ‘normal flow’
  • Pigs that were delayed on transfer 1 week.
  • Pigs that were delayed or ‘held back’ on several occasions up to 8 weeks.

The differences between these 3 flows are explained in detail in an article in the section "tips on pigs". In summary, the animals that were retained several times originated from sows with lower average parity. At slaughter, carcases from pigs retained several times had a much lower carcass weight (around 10kg) and higher variability. The following graphs show the scores for lameness (1 to 3), tail lesions (0 to 4) and respiratory lesions at slaughter (SPES and EP lesions) for the 3 described groups. The animals that were retained had a higher average score for lameness, pleurisy and EP lesions (figure 2). Whether these are the reasons these animals did not ‘keep up’ with the normal flow or are the consequence of not being in the normal flow requires further study.

Figure 2. Prevalence of lesions in slaughterhouse for the 3 flows of animals described.
Figure 2. Prevalence of lesions in slaughterhouse for the 3 flows of animals described.

This study singles out birth weight as a very important factor affecting productive performance and health of pigs up to slaughterhouse and shows the different flows of animals created when dealing with big batches of animals with high variability of weights.


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