Are we breeding PORKERS?

by Walter Scharlach, SPESFEED (Pty) Ltd.

The national performance results of pigs tested during 1997 where presented to the Pork producers AGM in Pietermaritzburg and are shown in the table below:

Results for traits measured centrally during 1997

Breeds	No	Age 86kg	FCR	Backfat	ADG	DFL
		(days)	(g/g)	(mm T2/3)	(g)	(%)
SA Landrace Boars	102	133	2.44	16	965	53.2
SA Landrace Gilts	98	138	2.65	17	904	52.6
Large White boars	282	132	2.31	15	1048	54.0
Large White gilts	264	139	2.54	16	945	53.7
Duroc boars	54	132	2.32	17	1044	52.7
Duroc gilts	49	136	2.56	18	954	51.7
All Boars	438	132	2.34	15.5	1028	53.7
All Gilts	411	138	2.57	16.5	936	53.2

The results achieved are reasonable for growth rate but disastrous for fat thickness and feed efficiency. This becomes clear if we compare the average backfat thickness of 16mm from these tests with commercial P2’s. According to the meat and livestock commission (MLC) in the UK, the average P2 of slaughter stock has decreased from 17.4mm in 1977 to 11.1 in 1996. This would imply that our current breeding animals have the same backfat thickness as the UK had 20 years ago. The general consensus at the meeting was that these results are not representative of the on-farm results, and that it is the diet that is making these pigs "excessively fat." The reasons for the poor results of the national performance test can however be explained as follows:

	A pig’s genetic potential is determined by its ability to grow lean meat. The lean meat deposition curve increases rapidly in the young growing pig, reaches a plateau and eventually decreases as the pig approaches maturity.
	Lean meat deposition is driven by the intake of feed energy and is limited by the animal’s genetic potential.

	Once the lean meat deposition declines pigs grow slower and will tend to fatten easily if the feed intake is not reduced according to the reduction in lean meat deposition.
	Any pig that consumes more energy than is required for maximum lean growth will channel the excess feed towards fat growth.
	At the testing station pigs are housed individually under near perfect conditions. These pigs therefor consume more energy than they would under commercial conditions. They therefore grow faster and reach their potential sooner. The test pigs will therefore fatten more readily due to a higher intake of feed energy.

Early maturing pigs reach their maximum lean deposition between 40 and 70kg live weight. The lean deposition declines rapidly thereafter. Late maturing pigs on the other hand will only reach their maximum lean deposition at 100 to 130kg live weight.

The above can best be explained by using the test performance of 2 pigs as an example. The growth curve is illustrated in figure 1 and the performance summary is shown in Table 1.

Table 1: Performance summary of Pigs A and B:

Parameter	Pig A	Pig B
Backfat (mm P2)	20	12
FCR (g/g)	2.63	2.46
Gain (g/day)	1171	1061

Pig A: Pig A is an example of an early maturing pig. It grew very fast to 75kg and dropped off rapidly thereafter. This pig fattened and had a poor feed conversion because its energy intake was not reduced in accordance with the decrease in lean deposition.

Pig B: Pig B is later maturing. Growth did not slow towards the end of the test period and although this pig grew significantly slower than Pig B (9.4% slower) it did not over-consume energy, and therefore did not tend to get fat. It therefor had a significantly improved feed usage (by 6.5%).

Summary and conclusion:

Early maturity is a general problem amongst our pig population. The consequences of early maturity are slowing of the growth rate towards the end of the growing period, grading problems in cases where barrows are produced, and an overall reduction in feed efficiency in cases where carcases of 70kg or higher are produced.
The lean growth of boars is approximately 10% and 15% higher than that of gilts and barrows respectively. Boars should therefor be tested to a weight that is 20kg heavier than the current slaughter weight. This will ensure that the test performance represents the whole growing period of slaughter stock. Boars should therefore be tested to 110kg. It may be a good idea to only start this test at 50kg live weight and measure the performance to 110kg.
We need to remember that late maturing pigs can also get fat if they consume more energy than what they need for maximum lean meat deposition. It is vital for any breeder to gear the voluntary feed intake to the genetic lean meat deposition potential of his stock.