25 February 2000

Pig grading on up-&-up

MEMORIES of our six-monthly veterinary advisory meeting last autumn still loom large, writes Jasper Renold. The main area of concern (On Our Farms, Dec 10) was the deterioration in carcass grading as growth rates improved and pigs grew heavier.

The grading has certainly improved since the specification of the final finisher ration was changed by our nutritionist Caroline Bevan of Banbury Agriculture. The original diet included 1.05% lysine and 13.5MJ/kgDE compared with the new diets 1.15% lysine and 13MJ/kgDE.

Pigs sent for slaughter in the second half of December and January show a significant reduction in the P2 backfat measurement at similar deadweights. Consequently there has been a big improvement in bonus payments above the base rate from the abattoir.

Discussing these results with Caroline and PIC highlighted the need for caution in establishing the factors influencing our results. In particular, Mick Hazzledine of ABN Pig & Poultry Division, an adviser to PIC presented a graph drawn up by Dalgety Livestock Marketing – now part of Allied Livestock Marketing which market our pigs. It analysed the backfat measurements of about 3m pigs over six years on a monthly basis. The results, standardised to 70kg deadweight, are shown in Fig 1. The P2 measurement varies by 0.5mm from the lowest value in March to the highest in Oct. Our own analysis of monthly averages over the past three years, also corrected to 70kgdw at 0.13mm increase per kgdw, shows a similar pattern. But there is a wider spread of over 1mm. Superimposed on this graph are the monthly averages for Nov, Dec 99 and Jan 00 which display a similar pattern. All that reveals we could have expected a small drop in P2 from Nov to Dec and a larger one to Jan. We feel fairly confident, however, that the drop of 1mm between Dec and Jan is significantly different from the expected drop of 0.3mm found in previous years.

But there is not yet a consensus of opinion as to the reasons for the shape of the graph. The usual suggestions are ventilation difficulties during the winter and at certain times in the summer, prevalence of disease at certain times of the year, change from old to new crop grain and in sources of soya.

We are considering whether to change back to the original finishing ration because our pigs may suffer an energy deficit in the colder weather.

The financial implications of the changes in backfat were examined in more detail by comparing two batches of pigs of similar average weight. The first sent before the ration change, was 149 pigs dispatched on the Nov 8 with the average weight of 73.67kg and P2 11.95mm. The second batch of 168 pigs was sent on Jan 24 with an average weight 73.57kg and P2 at 10.99mm.

Fig 2 shows the percentage number of pigs in each backfat range for both batches. To get the best payment at least 65% of carcasses must grade 12mm or less for a bonus of 5p above base rate. The Nov batch unfortunately achieved only 61.8% but the January batch reached 76.8%. We also need to minimise the percentage of pigs in the other bands. Pigs probing 13mm and 14mm (2nd grade) only get 2p above base rate, third grade pigs have 10p deducted from their base rate and fourth grade pigs are deducted 20p from the base rate.

The Nov batch achieved 1.26p/kg above base rate but the Jan batch achieved 3.64p/kgdw or 2.38p/kg improvement. That was worth more than £1000 a month.

The change in ration seems to have reduced the backfat in the boars to a much greater extent than the gilts, 1.25mm compared to 0.7mm.

That raises the question of split-sex feeding and delivering different rations to each. At present we could do this only in the Straw-Flow building. It would be a lot easier if we were wet feeding.

Comparison of carcass grading of boars and gilts


Boars Gilts

% ave Ave DWT Ave P2 % no Ave DWT Ave P2 % no

boars (kg) (mm) P2 <12mm (kg) (mm) P2<12mm

Pigs sent

8/11/99 42.9 74.0 11.72 67 73.4 12.1 58

Pigs sent

24/1/00 44.6 73.2 10.47 81 73.9 11.4 72