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How to reduce pig weight variability?

Published: June 29, 2016
By: Miquel Collel (Director, Scientific Marketing Affairs, Global Swine) and Olivia Azlor (Global Marketing Director, Global Swine), Merck Animal Health.
In a sector aiming at standardizing the final product at the maximum, variability in pig weight at slaughter age is still one of the major issues in the swine industry nowadays.
Why is pig weight variability important? – The world as a distribution and not an average
Producers often talk in terms of weight average, treating a batch as if it was a single animal. Consequently, the batch will be ready for selling when, in average, it reaches the optimal weight for slaughter. However, when these pigs will be evaluated, they will be considered individually: some will fall under the desired weight range, some will fall over (both carrying economic penalties), and only a few will fall inside the optimal weight range, reaching its full economical potential.
It is when we look at every group of pigs as a distribution instead of as an average that we quickly understand that, with the same average weight, the key is in reducing variance to get more animals falling within the desired range (D. DiPietri 2014).
How to reduce pig weight variability? - Image 1
 
How to reduce pig weight variability? - Image 2
Also, big differences in pig weight at slaughter age affect the optimal management of a farm, preventing the implementation of efficient all-in all-out programs.
When does variability start? - Variability in pig weight can start at birth. It has been widely documented that slight variations of piglet weight at birth amplify through the pig life causing (partially) the important differences that we can then find at slaughter age (Sergi López- Vergé & David Solà-Oriol, 3tres3 2015)
 How to reduce pig weight variability? - Image 3
 
This “amplification effect” has been differently quantified in literature: a difference of 0.73 g between the 10% and the 90% percentile at birth may become a difference of 4,73 kg at fattening (source? Graph below) or 1,1 kg of difference at weaning may become 3,8 kg of difference at 138 days of age (A. Vela ESPHM 2015).
Regardless of the numerical difference per se, what is clear is that trying to homogenize piglets’ birth weight could be a key factor to achieve more homogeneous pigs at slaughter.
How to reduce pig weight variability? - Image 4
However, and despite the theory being well known, the reality can’t be more different.
The reality in piglet weight at birth
How to reduce pig weight variability? - Image 5
 
Albert Vidal, Jornadas UAB 2014
If a batch of pigs at slaughter age are better described as a distribution than an average, same applies to just born piglets. Piglets born within the same farrowing period (assuming batch management) can fall within a large range of weights. In recent data presented in the UAB talks, it was shown that the difference between the 5% lightest and the 5% heaviest piglets can be of more Other impacts of piglet birth weight
Piglet birth weight impacts not only the final pig weight, as we have just seen, but it also has a strong influence on piglet survival rate, or better said, on pre and post-weaning piglet mortality.
How to reduce pig weight variability? - Image 6
Very recently A. Vidal demonstrated that the cumulated percentage of mortality (from day 0 to day 138) for the group of pigs coming from the lightest piglets in a specific batch (weighting less than 3 kg) could raise up to 33% whereas the mortality for the pigs coming from the heaviest groups ( more than 9 kg) was of about 0%.
Therefore there are two reasons why we should be aiming at reducing piglet birth weight variability: 
- to have more homogeneous pigs at slaughter
- to have less small piglets thus reducing piglet mortality
How old is a piglet at birth? - What causes piglet variability at birth?
We use to think that age at birth is 0 days, but this isn’t exactly true. At birth a piglet can be from 112 to 119 days old (ie. the gestation length).
We can say that variability in piglet weight starts before birth and comes from two sources. Indeed we have:
- Variability in piglets born from the same sow.
- Variability between piglets from different sows (different ages at birth).
Despite the first type of variability being badly understood and thus difficult to impact, we know some of the factors that explain the second type.
Variability within piglets from different sows can be explained, among others, by three main factors:
o Different conception date:
  • Sows come to heat at different days during the week.
  • Additionally, they are usually inseminated 2 to 3 times at different moments.
  • It is logic to think that not all the sows will get pregnant at the same time.
o Different birth day: for a single batch, if not synchronized, the farrows may extend during a whole week, giving birth to piglets of different ages.
o Semen from different males.
 
We end up having every day of the week as possible conception day.
Other impacts of piglet age difference at birth
Piglets born from the same batch of sows will usually be raised together. This means that they will be weaned at the same time, fed equally, vaccinated at the same moment and treated with the same dose of antibiotic (calculated from the average age of the batch and thus theoretical average weight).
However, as we have seen, they may have quite different ages, which means that they might still have different feed needs and might still be at different stages of the development of their immunological system.
Some of the consequences of this can include digestive problems, failures in vaccination or antibiotic over or under-dosing.
How can we homogenize piglet birth weight?
If we concentrate into reducing variability within piglets from a single batch and from different sows, we have two leverages to play with:
  • Synchronization of ovulation, of insemination and of parturition to obtain piglets with the same age.
  • A single insemination that would allow us using fewer males, thus selecting the best ones, and reducing genetic variability.
Fortunately nowadays we can find in the market solutions to work towards these goals, as would be:
  • GnRH analogues (such as buserelin) to synchronize ovulation and consequently needing only one insemination at a fixed time to achieve the same good results.
  • Prostaglandins (such as cloprostenol) to synchronize parturition.
If the fight against pig weight variability is far from being over, we have started understanding some of the factors we can influence to control and reduce it as much as possible.
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Allan Schinckel
Purdue University (USA)
4 de septiembre de 2016

Also the much of the economic impact of variation is at the pork processor level. Increased variation in Carcass weight causes increased variation in the cut weights. The distribution of carcass weight with serial marketing of pigs from a barn ( for example 25 % -- then 25% in 10 days and the remainder in 15 days) results in a non-normal distribution carcass weights. If pigs BW's are close to normal - serial cuts from a normal is not normal. We have done simulation and actual data that the accuracy in which pigs are sorted can double the stand deviation in the carcass weights of the pigs delivered. The amount of variation in carcass weight and the distribution of carcass weight is greatly affected by the accuracy in which pigs are sorted for market. Published in "The Professional Animal Scientist- 2016.

Allan Schinckel
Purdue University (USA)
4 de septiembre de 2016

The sources of variation for birth weight and their relative importance varies from species to species. In pigs, the genetic variation is greatest for the maternal effect and not the direct genetic effect. The uterine environment is the largest source of variation. In beef cattle, the direct effect have more genetic variation. In humans, the maternal effect is largest and the sire has little effect. My wife comes from family with long gestation lengths and gestation high sugars. My first son was born 12 lbs 12 ounces. The beef cattle boys ( profs) - posted a sire summary and put my name and EPD for birth weight of 12.75 -- and suggestion I should be culled as a cow killer. Well-- culling decisions of sires must be based on more than 1 offspring our of one dam -- but also in humans the sire has little impact on the birth of the offspring. The exact opposite of cattle. Horses are in between the sire and the dam breed have effects but if small breed large breed reciprocal crosses are made the larger offspring will be out the large dam breed.

Allan Schinckel
Purdue University (USA)
5 de julio de 2016
also the light weight piglets at birth are slowing growing (even at the same BW) and are less feed efficient (based on thousands of pigs with individual feed intake data). Light weight pigs less than 1.1 kg at birth can be 20 to 30 US dollars less profitable per pig than pigs with birth weights above 1.1 kg.. Light birth weight gilts in multiplier herds have lower probabiiity of research puberty in time to be selected and have lower litter size and longevity.
Egbert Frank Knol
Topigs
5 de julio de 2016

Genetic part of the equation. Birth weight is highly heritable, from the maternal side: some sow families give heavy piglets, others light. Heritable also means repeatable, sorting sows based on first and/or second litter birth weights will definitely create difference in third or later parity. Service sire, father of the piglets has very little to do with birth weight.
Within litter standard deviation is heritable too, at a lower level, but still. Genetic selection can reduce variation in birth weight. Unfortunately there is a high positive correlation between level and variation. Selecting for higher birth weight will give more variation and selection for more uniformity will make pigs lighter. Interesting challenge for breeding companies.

I fully support the proper sorting of piglets based on birth weight and day of birth, there is serious money involved in the proper management of the different groups.

Allan Schinckel
Purdue University (USA)
4 de julio de 2016
We have found that later BW's (168 d) or days to constant BW's (120 or 130 kg) to have linear-quadratic relationships with both birth and weaning weights. Also the BW gain the first two weeks after weaning is important. After birth, any management to increase the growth of the lightest pigs in the group can reduce variation. Each stress - disease - heat - social interactions from mixing etc, increase variation also. Note also the light weight pigs are birth and weaning are much less profitable than heavier pigs are birth and weaning. The lighter the pig at birth and weaning - the less valuable it is.
Paul Walker Thompson
4 de septiembre de 2016
Dear All I have extended experience with Synchronize Farrowing and we had great Piglet Birth Weight Variability. The advantage gained was Attended Farrowing, especially from ten to three o'clock during the day, The ability to flow All-In/All-Out. Paul Walker Thompson
Paul Walker Thompson
4 de septiembre de 2016
Dear All I have a hard time understanding how people are saying that the Sire has little to do with Birth Weights as the Boar offers have of the Genetic material of each and every pig. To select Low Birth Weight/ High Weaning Weights the Cattle Industry worked primarily with the Sire Side of the Equation! Please let me know where this thinking is going wrong! Paul Walker Thompson
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