Effect of vitamin A depletion on fat deposition in finishing pigs, intramuscular fat content and gene expression in the longissimus muscle

Nutritional strategies like reduction of dietary vitamin A have been proposed with the aim of increasing intramuscular fat (IMF) and improving the meat quality. The purpose of the study was to evaluate if reduction of dietary vitamin A would increase IMF, without affecting backfat deposition and pig performance parameters. Forty eight barrows were fed diets with different vitamin A levels: without supplemental vitamin A (0 IU vitamin A /kg; n=16), a level close to the requirement of NRC (1998) (1250 IU vitamin A/kg; n=16) or a level typically used in commercial formulation (5000 IU vitamin A/kg; n=16). The treatment without supplemental vitamin A did not affect growth performance parameters, only a trend to increase final body weight was observed when compared with animals fed with vitamin A in the diet. However, reduced perirenal fat and a trend to increase muscle depth between the 3th and 4th ribs was observed in the animals fed the diet with no supplemental vitamin A. These results suggested a reduction of fatness when vitamin A was omitted in the diet, contrary to the initial hypothesis. Intramuscular fat content was not affected by the reduction of the dietary vitamin A levels below the requirements; in fact the trend was opposite to the original hypothesis. The content of retinol in the liver was increased when the animals were fed higher levels of dietary vitamin A but animals fed without vitamin A diet also produced retinol, although in a reduced amount, which could explain the lack of effects of vitamin A reduction on performance. When comparing 5000 IU/kg with 0 IU/kg diets, only a trend in reduced expression of PPARα without impaired modification on fat content was observed in longissimus muscle. From this study, it can be concluded that omitting supplemented vitamin A does not affect performance, decreases perirenal fat and possibly overall fat deposition, without a significant reduction on IMF, contrary to the original hypothesis.