The sow caliper: Understanding body condition

Body condition is one of the most practical indicators of whether a sow is being managed in line with her physiological needs. It reflects the balance between nutrient intake, body reserve mobilisation, growth, lactation demand and recovery before the next reproductive cycle.

“This is particularly important in first-parity sows as they are still growing while also supporting their first litter, which makes them especially vulnerable to excessive loss of body reserves during lactation,” said Julia Adriana Calderón Díaz, scientific director of Prowess Bioscience.

“If a sow enters farrowing too thin, she may have limited reserves to support milk production and recovery after weaning. If she enters too fat, this can also create management challenges, including poorer feed efficiency, mobility issues and difficulty maintaining the sow within the desired body condition range across cycles.

“Good body condition management supports lactation performance, reproductive recovery, animal welfare and long-term sow retention.”

On farm, sow body condition is commonly assessed visually using various scoring scales. These methods are practical and quick.

However, score definitions can vary between people, and even the same person may score differently, depending on sow posture, lighting, time pressure or the number of animals being assessed.

This is particularly relevant when the objective is not only to classify a body condition at one moment, but to monitor changes over time.

The caliper

In recent years, swine breeding companies and technical teams have increasingly promoted more standardised approaches to sow body condition monitoring, including the use of the sow body condition caliper.

“This reflects a wider move to using practical, repeatable measurements to support feeding and management decisions. The caliper offers a simple way to make body condition assessment more objective and repeatable,” Dr Calderón Díaz said.

“It is quick to use, easy to implement on farm and provides a more standardised measure than visual scoring alone.”

The caliper is placed over the sow’s last rib area to assess the angularity of the body. This provides a numerical measure that can be used to classify sows into different body condition categories.

Used once, the caliper provides a snapshot of condition. Used repeatedly, it can show how condition changes across production stages.

This is particularly useful during lactation, when body reserves are expected to change but the direction, magnitude and management implications of that change can vary considerably between sows, Dr Calderón Díaz explained.

Research

To examine this in practice, caliper records from 1,424 first-parity PIC Camborough sows were analysed to quantify body condition change during lactation.

Records were collected on a commercial farm where the caliper had been implemented as part of routine body condition monitoring. The analysis focused on changes from entry to farrowing to weaning, including both average caliper change and movement between body condition categories.

Overall, sows lost 5% of body condition (measured in caliper units) during lactation.

“However, averages can hide important differences between animals and thus, to understand what this change meant in practice, it was necessary to look at where sows started and where they finished,” said Craig Lewis, PIC’s commercial director for the UK and Ireland.

At entry to farrowing, most sows were classified as either ‘ideal’ (56.1%) or ‘fat’ (29.9%). By weaning, the distribution had shifted.

The proportion of ‘ideal’ sows increased to 62.1%, while the proportion of sows classified as ‘fat’ decreased to 14.5%, suggesting that many animals moved towards a more desirable condition during lactation.

At the same time, the proportion of ‘underconditioned’ sows almost doubled at weaning, indicating that a relevant proportion lost enough condition to finish lactation below target (see graph below).

Indeed, individual caliper value change varied considerably, with some sows losing up to 40% of their initial caliper value, while others gained as much as 30%.

Lactation transition

A closer look at how individual sows transitioned from one body condition category to another during lactation showed that 37.1% of sows remained in the ‘ideal’ category.

This is the type of pattern most producers would aim for, Dr Lewis explained. In addition, 18.8% of sows moved from fat to ideal, likely reflecting controlled mobilisation of body reserves during lactation.

In contrast, 13.4% of sows moved from ideal to underconditioned, while 3.3% moved from fat to underconditioned, suggesting a more marked depletion of body reserves during lactation (see graph below).

However, not all body condition transitions were towards lower condition categories. About 5.5% of sows moved from ‘underconditioned’ to ‘ideal’, which may indicate recovery or improvement.

Another 5.5% of sows moved from ‘ideal’ to ‘fat’, and smaller groups moved to obese categories. “These changes highlight that not all losses are bad, and not all gains are good,” Dr Lewis said.

Management information

The value of looking at caliper transitions is that they help turn body condition records into management information showing which groups may need closer attention.

This can support more management discussions around lactation feeding, feed intake, litter demand, gilt development and recovery before the next service.

A simple framework for interpreting selected caliper transitions during lactation is shown in the table below.

“These results suggest the value of the caliper is greatest when measurements are used to support decisions, not simply to describe condition at a single time point,” Dr Lewis said.

“Measuring at entry to farrowing and weaning provides a useful overview of how condition changes during lactation.

“Adding a mid-lactation check for higher-risk females, such as underconditioned sows, sows nursing large litters or groups where previous batches showed excessive condition loss, may help assess whether the current management strategy is working while there is still time to adjust it.”

At herd level, caliper records can also support more focused reviews. Once condition is recorded consistently, results can be summarised by parity, batch, feeding group, litter size or starting condition category.

This allows producers to move beyond general impressions of whether the herd looks thin or heavy, and ask more specific questions: which sows are changing, how much are they changing and are they moving to or away from the desired condition range?

“For farms not yet using the caliper routinely, the practical starting point does not need to be complicated,” Dr Calderón Díaz said.

“Measuring consistently at key time points, recording the results clearly and reviewing patterns across groups can already provide useful information. The aim is not to collect more data for its own sake, but to make body condition change easier to interpret and easier to act on.

“Ultimately, the caliper provides a simple way to quantify changes in condition during lactation. The management value lies in understanding whether that change is appropriate for the sow’s starting point, whether it is happening in specific groups and whether it is identified early enough to act.”