Members of the research consortium between AFBI, Devenish Nutrition Ltd, John Thompson and Sons Ltd and PCM (from left to right) Wallace Henry, Raymond Bradford, Marion Scott, Alan Thompson, Fred Gordon, Alan Ashenhurst, Alistair Carson and Elizabeth Magowan (absent from the picture is Elizabeth Ball, Kelvin McCracken and Violet Beattie).

Diets made by compounders are commonly finely ground and in pellet form, whereas diets made in home mixing operations are normally more coarsely ground and usually in meal form.

As expected, it takes more energy, and is therefore more expensive, to produce a finely ground pellet compared with a coarsely ground meal diet, aside from the extra mechanical equipment required. However, previous research has suggested that offering pigs feed in pellet form improves feed use efficiency.

Furthermore, other research studies suggest that when particle size within the feed is small (i.e. fine) feed use efficiency is better than when the particle size is large (i.e. coarse). However, few studies have investigated if these two processes i.e. pelleting and fine grinding, have cumulative benefits on feed use efficiency.

In the current study, two trials were conducted. In both trials the ingredients (main ingredients being barley (41 per cent), wheat (36 per cent) and soya (19 per cent)) and nutrient specification (digestible energy of 13.6MJ per kg, crude protein of 16.7 per cent and total lysine of 9.6g per kg) of all diets were the same. The only differences between the diets was the ‘form’ in which they were offered, i.e. meal or pellets and the particle size within them i.e. ‘fine’ or ‘coarse’.

The finely ground diets were manufactured using six 4-mm screens and the coarsely ground diets were made using a combination of two 14-mm and four 10-mm screens. The particle size profile of the diets after ‘fine’ or ‘coarse’ grinding is reported in Table 1. The coarsely ground diets had a similar particle size profile as those generally adopted in home milling operations.

In both trials, pigs were offered feed from a wet and dry single space feeder (Verba feeder).

In trial 1, when pigs on a commercial farm in mid Ulster (Tempo and PIC337 crossbred pigs used) were offered feed in either meal or pellet form, their growth rate between 55 and 110kg was similar (881g per day). However, although there was no significant difference, a numerical improvement of three per cent in feed efficiency was observed when pellets were offered instead of meal. For the commercial herd, there were issues regards separation of the meal diet due to the blowing of the diets into the bulk bins. Although these issues were reduced when the feed was blown in with less force, it does raise concerns regarding the use of meal in auger systems.

In trial 2, pigs on the AFBI research herd (Tempo crossbred pigs) were offered diets which were either finely or coarsely ground and in either meal or pellet form. Table 2 reports the performance of pigs and feed cost calculations when these four diets were offered on the research herd. Similar to the commercial herd, the growth rate of pigs was similar for all diets (917g per day) (Table 2). However, daily feed intake was lowered by 4.5 per cent and feed efficiency was improved by 5.5 per cent when pellets were offered compared with meal in trial 2 (Table 2). Feed efficiency was also improved (by 3.1 per cent) when the particle size was ‘fine’ compared with coarse (Table 2). The beneficial effects of pelleting and fine grinding appear to be cumulative and economically large differences in feed cost were calculated.

This study suggests that a £20 per tonne differential in diet cost is required in order to compensate for the deterioration in feed efficiency when a ‘coarse meal’ was offered compared with a ‘fine pellet’. Overall, it cost an extra 1.8p for each kilogram of live weight gain during finishing when meal was offered compared with pellets. There was no effect of diet form (meal or pellets) or particle size (fine or coarse) on stomach ulceration in either trials. Furthermore, there were no effects on carcass quality, i.e. back fat depth or kill out percentage.

Conclusion

In agreement with previous research, feed efficiency was improved when diets were offered in pellet form instead of in meal form. When the particle size within the diet was ‘fine’, feed efficiency was also better than when particle size was ‘coarse’. Furthermore, the effect of pelleting and fine grinding appeared to be cumulative and economically large differences in feed costs would be required to compensate for differences in feed use efficiency.