There is, you might say, a strong element of guesswork involved. Pig producers rely on peripheral information such as whether pigs seem to be comfortable, healthy and exhibiting normal behaviour. It can be difficult to tell whether pigs are growing well in this way.

This case study looks at two indirect ways of looking at the metabolism - by heat output and by water intake - measured by simple hardware in a regular production situation - and relates the two.

Heat output

Pigs produce heat as a by-product of digestion. This heat keeps the animal warm, but is constantly lost to the surrounding environment.

In environmentally controlled housing, this heat is conserved in the building to a greater or lesser degree. Whilst all the heat is ultimately lost to the outside air, keeping it around the pig places far less stress on the pig's own ability to retain heat. The building is, as it were, a big blanket around the pig.

The environmental control system of the building aims to keep the building at a constant temperature. By measuring the amount of heat removed by the control system, we can measure (approximately) how much is being lost by the pig. Heat is also lost through the structure of the building, so it's necessary to adjust for structural heat loss also.

Water intake

Heat is produced as a by-product of digestion, so the amount they eat should determine their heat output. Feed delivery can be and often is measured by auger run time and/or weighing systems, but it can also be measured by means of water intake.

Dry fed pigs drink water in proportion to the amount they eat, and it's desirable to measure water intake for other reasons - such as to check for normal behaviour, and for veterinary purposes. In most cases, it's easier to measure water accurately and continuously than feed as such.

These Barn Report charts from a Dicam control/logging system show inside and outside temperatures (top chart) and daily water use v daily heat loss (bottom chart) over a period of 30 days in weaner/grower accommodation holding 330 pigs.

In the top chart (temperature) note that room temperature (red line) is kept constant at about 20ºC, although outside temperature varies considerably. The spikes in the outside trace are due to sun exposure of the outside temperature sensor for a couple of hours on some days, so they don't always show true outside air temperature.

In the bottom chart, water is measured by means of a flow sensor in line with the header tank (red line). The logging system counts each revolution of the flow sensor and adds up use over each 15 minute period. In the display shown here, they are totalised for each day. (For behavioural and other purposes, it is usual to show use in each 15 minutes, omitted here for simplicity.)

Heat removal/loss is calculated by means of temperature difference between inside and outside, and approximate ventilation rate.

Ventilation rate is calculated from the running speed of the fans (as set by the controller) and the estimated full capacity of the fan. For example, the capacity of the first fan stage is specified as 15,000 m3/h, so when it is running at 20 percent speed, the ventilation rate is calculated to be 3,000 m3/h.

Ventilation heat loss is calculated according to estimated ventilation rate and inside/outside temperature difference. Structural heat loss is calculated from building dimensions and assumed U value. Figures for each 15 minute period are totalised for each day.

Temperatures are shown in ºC. Heat removal (including structural heat loss) is shown as kWh per day of sensible heat. Water is shown as total daily consumption in litres.

Discussion

With this particular data, heat loss tends to be slightly under-estimated because of some errors in the outside temperature reading. The outside temperature sensor shows it warmer than it actually is, and therefore less heat would be lost for any given temperature inside.

Over the period, ventilation rate varies considerably in response to changes in outside temperature, and variations in pig heat output.

In general, the two different methods show very similar relative changes. Both water use and heat loss/removal go up by roughly 72 percent from the starting value.

Chart two shows more extensive data over a longer period for more rooms. Each dot correlates the (calculated) heat loss/removal on that day with the water use in the room on that day. There are 4 rooms in total, with 412 data points altogether.

The data suggests a correlation between heat produced and water used of roughly 2kWh of heat produced for every litre of water consumed. The relationship is not absolutely fixed and varying, but they are clearly related in a linear manner over a fair range of values.

Discussion

The data shown in chart three suggests that both water intake and heat loss from the building are reasonably good measures of pig metabolism. As the pig grows it eats and drinks more and it produces more heat. So to some extent the two confirm one another. If, say, both the heat calculation and water intake show changes in a direction we don't want, we should take it seriously. Differences between one room and another, or one batch and another suggest a real, rather than arbitrary change.

In this data from a batch of pigs in another room, we can see that both water and heat rise steadily, but then flatten off and fall slightly (generally similar to the other batch shown previously).

The fact that they follow a similar pattern suggests strongly that this is a real fall off in the performance of the pigs. As a single event, a producer might consider this due to any number of reasons, including a change in the weather (causing that good old favourite "draughts") or illness. In fact, data from a number of batches - where the pattern is often but not always repeated - suggests it may be due to a change in feed ration. It may be the pigs don't like the change in taste, or find it less digestible, say.

The data doesn't indicate a reason - though it does tend to rule out any direct environmental factor such as temperature - but does suggest it regularly happens. Pigs probably continue to grow, but at a reduced rate than before, as shown by their reduced intake and metabolic throughput.

Eliminating this bottleneck to growth could give significant returns in terms of improved weights or reduced days to finish. If the change (whatever it is) represents a stress as such, it is - as many stresses - liable to have an unequal effect across the range of animals. Reducing the hold up may therefore also reduce variability.

It's worth noting that heat output of the pigs is the main factor in determining whether or not buildings are able to achieve target temperatures - alongside the target temperatures and minimum ventilation rates as determined by the livestock keeper. The heat loss estimation technique offers a relatively simple way of finding whether issues over achieving temperatures are due to pig output, stocking rates or characteristics of a ventilation system.

Summary

The data shown here suggests that measuring water intake and calculating heat loss from growing and finishing accommodation may be worthwhile as a metabolic indicator. On the face of it, water measurement may be a reasonably self-consistent way of estimating metabolic heat production and be a good indicator of growth.

Although the methods used give only indirect estimates, they are relatively easy and cheap to measure (given the right logging and monitoring system). Considerably easier, cheaper and less invasive than, say, regular weighing.

In the past, producers have tended to view production monitoring merely as a way of looking for problems. (And for many, an unnecessary frill if there are adequate livestock keeping skills.)

However, the data shown here suggests that these methods offer a cost-effective way of examining the process and procedure of pig growth at minimal interruption and low cost in a standard production situation.

Water is easily measured using flow sensors. Heat loss/removal calculation is less directly measure, but readily achieved given simple instrumentation and the power of modern computers. Combined, they have considerable potential for monitoring pig production.

In the study shown here, the basic instrumentation was the Dicam control system and the only additional hardware was water flow sensors. Calculations (to estimate heat balance) and data presentation to combine water and heat balance data are carried out automatically by the Barn Report data system. The views shown here are from Barn Report screen captures.

Source: FarmEx - February 2005