By Dr Peter Evans, veterinary consultant

Part one of a two this article will deal with the basis of growth monitoring. Part Two will attempt to define corrective actions if targets are not reached.I. WHY

A. Establish growth pattern

More often than not the only growth figures available on the average S.A. pig farm are (a) weaning weights (b) 70 day weights (c) market weights, and (d) estimated age at market. The guess work needs to be eliminated from judging how well pigs are growing at any one time. It is important to be able to assess how well one is doing in relation to other farmers who have similar conditions. In the present “easy” economic climate it may seem unnecessary to analyse growth intensely as profits are being made. However, as we all know changes do occur in the economies of pig farms and survival may only be possible if efficiency is optimised.

The broiler industry (Pork’s biggest competitor in the market place), realised the importance of efficient growth and there are curves drawn of expected growth of broilers, feed intakes, water intakes and FCR’s on a daily basis. If there is any deviation it is quickly identified and correction timeously instituted. The pork industry needs to become more efficient in optimising production so as to maintain its competitiveness in the meat industry.

The typical growth curve of the pig follows a sigmoidal shape. Firstly, an acceleration-phase where ADG is continually rising followed by a phase of constant growth and then a phase of deceleration (which occurs at about 6 months of age), see graph (figure 1).

It is also important to know the difference in growth and efficiency performance of different sexes of pigs. Typically boars yield leanest carcasses followed by gilts and then barrows. Boars also are more efficient followed by gilts and then boars. However when comparing ADG’s the order is boars, barrows and then gilts. (This will be elaborated in the next article.)

Typical growth curve

The pig’s ability to lay down muscle (i.e. rate of lean tissue growth) declines with age and simultaneously its requirements for protein and lysine levels to support optimal growth decline. A fairly dramatic break-point of decline in meat deposition rate is reached.  In a study done it was shown that at birth the ratio of fat: muscle was 0.13 (i.e. lean) and by 28-weeks of age had changed to 1.09.

Figure 2: Total vs Meat depostion

In the graph showing total deposition and meat deposition rates (Figure 2); the area between the lines represents fat. Purposefully age or weight values are not included on the X axis, as the break – point value varies. Typically the break – point would only be reached at about 60 kg live mass. The point varies depending on genotype, environment, management and most importantly nutrition i.e. it is farm specific. Measuring P2 would enable one to predict this point in a herd and thus enable one to adjust nutrient levels for optimal lean growth and eventual carcass quality.

Possible methods of achieving ideal nutrient presentation are constantly being researched. Phase feeding (different rations fed for short periods), where especially protein levels are changed are the most popular. A second idea is choice feeding – two rations of different specifications are presented simultaneously. It seems as if pigs are able to balance their nutrient intake with their nutrient requirements.

A further reason for drawing a growth pattern curve is to enable identification of periods or points in the growers production cycle where ‘dips’ in production may occur. These ‘dips’ could be related to stresses imposed on the pigs by management. Remedies could then be found to try and ensure continued optimum production.

B. Measure Average Daily Gain

Measuring ADG is important in that it indicates the level of performance being achieved by the pig. Indirectly & directly indicates whether variables such as genetics, nutrition and environment are allowing optimal production.
ADG is also used as an indicator of genotype. Better genotypes will grow in the region of 830g/day over the live mass range from 25 to 85 kg, the average 750 g/d and the poorer genotypes < 700 g/d.

Also we wish to make sure that ADG curve follows a normal pattern. The ADG rises fairly rapidly and then reaches a plateau. (Figure 3)

Figure 3: ADG curve

C. Feed conversion ratio

The feed conversion ratio is the measure of efficiency in the production process at any point in time. It measures the quantity of material (feed) converted into product (meat). Ideally lean tissue FCR should be measured as the price for product is based heavily on lean meat yield. However it is expensive and relatively inaccurate to measure P2 in the live animal, which is then used to calculate lean meat yield.

As the pig grows the FCR deteriorates due partly to the fact that progressively more fatty tissue is deposited in relation to lean.

II. HOW

A. Bias

Bias is defined in a trial as any influence that may be exercised by the researcher on the results; for example, only choosing the better pigs to put on trial or only pigs originating from certain sow/boar lines. Results from these trials are useful only if it is clear that they refer to selected animals and not to the farm in general. All possible bias must be eliminated.

To eliminate bias as much as possible and to record the average performance of the farm the following suggestions are made:-

a) Discard the best and the worst group of that weeks weaning. (If all the weaners are going to be put on test then this does not apply).

b) Pick the number of groups as randomly as possible e.g. put pen numbers in a hat and draw, or roll a dice.

c)  Make sure – if you are separating sexes – to have equal numbers of each of each sex on test.

B. Sample size

A formula is available to determine sample size. If we assume the following:- weight spread in a group will not exceed 10 kg and we want the sample to estimate within 2 kg of the true average weight at a confidence level of 95 % then sample size should be 100 pigs. But if we use 5kg and 2 kg the sample size would be 25 pigs. In practice however sample size should at least exceed 50 although “statistically” this number is insufficient.

C. Feed monitoring

Of all the areas in growth monitoring trials, feed monitoring is the most difficult. To calculate FCR and feed intake accurately feed used needs to be precisely measured.

a) The weight of feed going into the hopper needs to be recorded. Tagging &/ numbering bags which have been pre-weighed seems to work.

b) The accurate measure of feed in hopper at end of trial period. (Either weekly or every second week). Feed on floor must not be included – it can be recorded apart, could prove interesting.

c) Could consider using trial hoppers which are equipped with load cells which record amount of feed dropped into hopper or amount of feed remaining.

d)  Trial pens in a particular part of each and every house could make managing the trials easier.

e)   All in all out system makes continual monitoring of whole herd very easy. The bulk tank supplying the house could be fitted with a load cell to help monitor feed use. The number of pig days in the house would be recorded as well as weights at entry and exit. All parameters for growth monitoring could then be calculated.

Measuring water intake in a group of pigs on a daily basis will give indirect assessment of changes in daily feed intakes. (Another lesson from the poultry industry).

D. Accuracy & completeness

No occurrence should go unrecorded. For instance any disease or change in feed or change in raw material or change in housing etc.

Must include removed pigs and the time that left the group. We use no. of pig days to compute ADG and daily intakes. If removals are not recorded accurately the above become less accurate.

Temperatures and seasons will allow prediction of growth patterns for various times of the year. Alterations in management, environment and nutrition to accommodate the needs of the pigs could be timeously made.

Motivate labour – if they know what they are doing and why, the researcher is more likely to get their co-operation

SUMMARY

In this first part we have examined the why and how of growth monitoring. Anyone who has been involved with pigs can attest to the difficulty of growth and feed monitoring and it is safe to say that those with all-in-all-out facilities can monitor the parameters discussed above relatively easily. It is however important to note that those who have decided to do proper growth monitoring all report and are convinced of the financial advantage gained.

The performance of the grower herd has a huge financial influence on a farm’s profitability. It therefore stands to reason that as much attention (if not more) should be paid to tracking performance tendencies as is paid to reproductive performance.