What limits growth in piglets?
We all know very well that young pigs fail to realise their full potential for growth, at least in the period immediately post-weaning. With this statement, I would like to invite our readers to contribute their thoughts on the reasons or factors that limit post-weaning growth and (or) feed intake. My own thoughts on this very controversial topic are below:
The major drive for growth in post-weaned pigs is believed to be feed intake, or rather more correctly, energy intake, as it has been demonstrated very clearly by Campbell et al. (1975). Under this understanding, it appears the failure to provide nutrient-dense diets is one of the major reasons why growth is depressed in young pigs.
Genetics & Sex
It appears genetics and sex play only a minor role, if any at all, at the post-weaning phase, with a few studies showing gilts having a slightly higher feed intake. Under practical conditions, however, these two aspects are not significant enough to cause marked differences in performance post-weaning.
This appears to be the most widely-talked issue today, yet it is only lately recognised at least in the proper magnitude of significance for growth and feed intake post-weaning. Under the best commercial conditions, pigs are exposed continuously to a myriad of pathogenic and non-pathogenic micro-organisms. Even though disease may not always prevail, chronic exposure to antigens constantly triggers the immune system and causes sub-clinical disease symptoms that are difficult to identify and quantify. Chronic activation of the immune system reduces appetite, increases muscle protein degradation, reduces muscle protein synthesis, and diverts nutrients to the synthesis of components of the immune system such as acute-phase proteins. The negative effects of chronic activation of the immune system (i.e., sub-clinical disease) in pigs reared under immunological stress are illustrated in the following table.
It is now understood that stress affects negatively the immune system depressing feed intake and growth, not only in weaned pigs but also in all other phases of production. Pigs exposed to multiple management stress factors have their growth performance depressed in an 'additive' or cumulative pattern. As a rule of thumb, each stress factors depresses growth by about 10%.
So, in your opinion what else is missing from this list?
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