Carcase effects from a fast start

Feeding the weaned piglet for rapid early weight gains will establish good growth patterns through to slaughter without adversely affecting the value of the resulting carcase.

An important question relating to piglet nutrition has been investigated recently, with encouraging results. The overall message from this British work is that there is no adverse effect on carcase backfat from pushing piglets hard at the start in order to secure good growth right to slaughter weight.

The close relationship between early feeding and later weight gains had already been established by international studies. In the USA, for example, research at the University of Illinois confirmed that the major elements determining growth to slaughter were weaning weight and particularly the weight gained immediately after weaning. Previous trials with about 5 000 pigs at our own Greenhill Farm unit have shown clearly that about 30% of the variation in growth rates to slaughter are controlled by post-weaning performance coupled to weaning weights.

Experimental evidence not only in Europe, but also in America and Australia, has meanwhile exposed the myth of compensatory growth. Slow-growing young pigs do not grow faster at a later stage to catch up with the others in the group. Poor weight gains in the early weeks of life (and especially in the post-weaning phase) therefore mean that the pigs are confined to a lower growth curve throughout their subsequent growing and finishing periods. It can add 10-20 days to the time until they are ready for marketing.

Lately, we have been working with Newcastle University in the UK to examine how piglets liveweight gain in the late suckling period relates to their growth after weaning. The pigs were offered creep feed from 10 days old and weaned at 28 days before being followed through to 56 days. Once again, their weaning weight appeared to be a good indicator of post-weaning performance. One interesting observation was that the heavier piglets seemed more prepared to approach and explore the feeder immediately they were placed in the nusery pen.

The obvious conclusion from all this is that we want piglets to be eating and growing as quickly as possible, up to weaning and beyond it. In that way we will keep them close to their genetic potential for rapid growth when they reach the finishing house.

Until now, hoever, it has never been determined how growth patterns in early life affect the ultimate carcases. Some concern existed on this point. The worry was that pigs growing rapidly at the start and then up to slaughter would lay down too much fat so their carcase composition suffered.

But this belief has been based largely on studies conducted many years ago with animals which would be cinsidered today as genetically unimproved. It needed to be re-examined using modern genotypes.

Therefore we set up a trial in association with JSR Genetics, invloving 4 dietary treatments to provide different planes of nutrition during the weaning and early grower phases. In the first 3 weeks after weaning at 28 days old the pigs were allocated to either a High or a Low specification diet. They then went onto High or Low treatments until changing to ad lib feeding for the final stage to about 90 kg liveweight.

Growth and carcase characteristics were examinded in detail for a total of 256 pigs. The weight gains (set out in Table 1) closely resemble those seen previously and so reinforced our view that an additional kilogram on the weaning weight or an extra 100 grams/day of post weaning growth can reduce time to slaughter by 10-15 days. More notable for us in this instance was that the carcase data revealed no significant differences in fat deposition in all groups of pigs at slaughter.

As Figure 1 shows, the data in fact indicated a slight increase in lean tissue depostion (carcase muscle depth) for the pigs on High/Low and High/High treatments. You can see from Figure 2 that the group fed High after weaning and High again in the early grower phases did have slightly more subcutaneous fat at the P2 measuring point. But the difference was just 0.2mm. Such a small amount was not only insignificant statistically, at this level it would be undetectable on commercial farms.

So it is possible to feed piglets for rapid early growth and reap the benefits of a reduced slaughter age without losing out on their eventual carcase value. Animal scientists will be pleased to hear it fits with Huxley’s so-called allometric theory of growth (later substantiated at cambridge University in the UK by Sir John Hammand). The theory states that growth will always follow orderly and predictable patterns. For nutritionists and producers it carries the reassurance that whatever we try to do with pigs nutritionally, they will always have the potential to acheive the same body proporations as determined by their genetic capacity.

Date published: 2006-03-23

Dr Mike Varley