From Weaned Piglets to Kilograms Weaned: A New Perspective on Farrowing Efficiency

By Gabriel A. BonaTechnical & Commercial Development Manager – Latin America, Tonisity International

For many years, the number of piglets weaned per sow per year has been regarded as one of the most important indicators of efficiency in pig production. It remains an essential benchmark, as it captures key performance factors including litter size, farrowing frequency and pre-weaning survival.

However, modern pig production has evolved.

Genetic progress has significantly increased litter sizes, but it has also introduced new challenges: lower average birth weights, greater within-litter variation and a higher proportion of vulnerable piglets competing for colostrum, milk and teat access.

As a result, simply asking how many piglets were weaned may no longer provide the full picture.

Perhaps the more relevant question today is: How many kilograms did the farrowing house produce, and what quality of piglets entered the nursery?

Bigger Litters, Greater Challenges

A systematic review and meta-analysis found that an average increase of 4.8 piglets per litter was associated with approximately a 10% reduction in average birth weight and a 12% reduction in the average weight of live-born piglets. Birth weight variability within litters also increased.

In practice, this means that while larger litters can produce more piglets, they also tend to generate a greater proportion of lighter and more heterogeneous animals.

These piglets deserve particular attention.

In a study involving 4,068 piglets, animals weighing 1.11 kg or less at birth represented only 15.2% of the population, yet accounted for 43% of all pre-weaning mortality. Mortality reached 34.4% within this group, compared with 8.2% among heavier piglets.

The 1.11 kg threshold should not be viewed as a universal cut-off. Genetics, parity, management and environmental conditions all influence risk. However, the study clearly demonstrates that a relatively small proportion of lightweight piglets can account for a substantial share of farrowing house losses.

Why Measure Kilograms Weaned?

The number of piglets weaned tells us how many animals survived.

Kilograms weaned adds another dimension by measuring how much growth was achieved during lactation.

The calculation is straightforward:

Kilograms weaned = Number of piglets weaned × Average weaning weight

Consider the following example:

• 13 piglets weaned averaging 5.5 kg = 71.5 kg

• 12 piglets weaned averaging 6.5 kg = 78 kg

If only piglet numbers are considered, the first litter appears more productive.

However, when total kilograms produced are evaluated, the interpretation changes.

This does not suggest that losing a piglet can simply be compensated for by producing heavier littermates. Mortality remains a biological, economic and welfare loss.

Instead, it highlights that piglets weaned and kilograms weaned answer different questions, and both should be assessed together to obtain a more complete understanding of farrowing performance.

This concept is already reflected in applied research. A study involving 150 commercial farms and more than 135,000 sows simultaneously evaluated weaning weight, kilograms weaned per sow per year and sow feed conversion efficiency. The analysis showed that factors such as lactation length, nutrition, housing and management were associated with these production indicators.

Kilograms weaned is therefore more than a theoretical concept—it is a practical metric that broadens the assessment of production efficiency.

Not Every Kilogram Carries the Same Value

Even kilograms weaned has important limitations.

The first is weaning age.

Piglets weaned at an older age will naturally be heavier. Comparing weights without accounting for lactation length can therefore lead to misleading conclusions.

The second limitation is uniformity.

A litter may achieve a high total weaning weight while masking significant variation between piglets. A few exceptionally heavy animals can conceal the presence of numerous lightweight piglets.

Although total kilograms appear satisfactory, the nursery receives a heterogeneous group with different feed intake potential, growth capacity and resilience to health challenges.

For this reason, average weaning weight should be interpreted alongside:

• Coefficient of variation in weaning weight

• Proportion of piglets below a critical weight threshold

• Pre-weaning mortality

• Average weaning age

The third limitation is post-weaning performance.

Producing more kilograms in the farrowing house is valuable, but the true worth of those kilograms depends on whether piglets can maintain feed intake and continue growing once maternal milk is no longer available.

Weaning combines several major stressors simultaneously: separation from the sow, environmental change, social mixing and the transition from a liquid to a solid diet.

Under these circumstances, it is not only the piglet's body weight that matters. Equally important is whether the piglet is prepared to locate feed and water quickly, establish voluntary intake and maintain intestinal function throughout this critical transition.

The Farrowing House Must Prepare Piglets for the Next Stage

Weaning takes place in a single day, but a piglet's ability to cope with it begins developing from birth.

Colostrum intake, thermal comfort, milk access, health status, litter management and early nutritional support all influence growth, resilience and survival.

This also changes how interventions in the farrowing house should be evaluated.

Rather than asking whether a strategy simply increased average weaning weight, producers should consider:

• How many additional kilograms were produced?

• How were those kilograms distributed across the litter?

• Was the proportion of lightweight piglets reduced?

• Did the benefits continue after weaning?

• What was the cost of achieving those results?

An intervention that increases body weight but requires excessive investment, or fails to improve subsequent performance, may increase production without improving overall economic efficiency.

From a Single Metric to a Broader Efficiency Dashboard

Piglets weaned per sow per year will remain an essential performance indicator.

However, kilograms weaned introduces an additional dimension by combining survival and growth into a single measure.

Neither metric should be interpreted in isolation.

A more comprehensive farrowing efficiency dashboard should include:

• Piglets weaned per sow per year

• Kilograms weaned per sow per year

• Age-adjusted weaning weight

• Litter uniformity

• Proportion of lightweight piglets

• Pre-weaning mortality

• Early nursery performance

• Cost per kilogram produced

The industry is gradually moving beyond counting piglets towards evaluating kilograms weaned as a broader measure of productivity.

Yet true efficiency is not simply about producing more kilograms before weaning.

It is about delivering more uniform piglets with stronger feed intake potential, a well-developed intestinal system and the capacity to continue growing successfully after weaning.

Ultimately, the objective is not simply to wean more piglets, but to produce piglets that are truly prepared for the next stage of production.

References

FELDPAUSCH, J. A. et al. Birth weight threshold for identifying piglets at risk for preweaning mortality. Translational Animal Science, 2019.

MOREIRA, R. H. R. et al. Variability of piglet birth weights: A systematic review and meta-analysis. Journal of Animal Physiology and Animal Nutrition, 2020.

PANZARDI, A. et al. Newborn piglet traits associated with survival and growth performance until weaning. Preventive Veterinary Medicine, 2013.

PIEROZAN, C. R. et al. Herd-level factors associated with piglet weight at weaning, kilograms of piglets weaned per sow per year and sow feed conversion. Animal, 2020.

About the Author

Gabriel A. Bona is a veterinarian with an MSc in Veterinary Sciences specialising in swine reproduction. He works in Technical and Commercial Development for Latin America at Tonisity International, supporting producers and distributors through science-based nutritional solutions for early-life pig performance.