• muscle fibers
• meat quality
• Maremmana
• liquid rumen
• lipid metabolism
• histochemical charactersitics
• heat stress
• fatty acids
• DMAs
• cortisol
• biohydrogenation
• beef
• Aubrac
• rumen microbiota
• seurop
• Steers

The present PhD Thesis were performe in order to better understand differences in the metabolic and productive response of two traditional breeds to different farming system on twenty Maremmana steers and twenty Aubrac steers that were allotted in two management conditions: feedlot or grazing system.
In the fist trial, in vivo evaluation of growth rate and chronic and acute stress were assessed. Besides, postmortem evaluation such as carcass traits, beef yield and finally physical, chemical and nutritional beef quality were measured.
In the second trail the effect of two feeding regimens (Feedlot or Grazing system) on the rumen microbiota compositions of AU and MA breeds were evaluate. Additionally, FAs and DMAs composition of rumen liquor was investigated in order to assess the association with changes in the rumen microbiota composition as affected by breed and feeding regimen effects. Finally, in order to obtain an overview of the mutual relationship among microbiota and rumen FAs and DMAs, the microbiota composition was associated to DMAs, OBCFAs, and to the BH FAs composition through the Principal Component Analysis (PCA).
The third trail was aimed at studying the effect of breed and rearing system on histological characteristics, proximate composition and myoglobin concentration on two muscles: Triceps brachii (TB) and Semimembranosus (SM)]. Furthermore, in order to deeply understand the biology of a muscle fibers and their relationship with lipids metabolism, the transcriptome analysis of 18 key metabolism-related genes were carried out.The results of the first trial showed that it is possible through a proper integration of concentrated, to produce beef from grazing steers without negative effect on quality parameters for tenderness and color also in the harsh environment of the Mediterranean area. Data about metabolic response of animals, showed that both breeds were able to overcome the critical environmental conditions of the Mediterranean summer .
Interestingly, the interaction breed x farming system was significant for hair cortisol content. MA steers in feedlot and AU steers on pasture showed the highest cortisol concentration, whereas MA steers on pasture and AU in feedlot had the lowest content of cortisol in the hair.
As regard the conformation of the carcasses, the AU breed had the better conformed carcasses compared to those of MA in both rearing systems, The MA breed had a score comparable to good, while those in the pasture for the most part they received a score comparable to quite good. As for the fattening state, the MA feedlot showed an average
The results of the second trials showed that the breed factor was the main factor affecting the rumen microbiota composition, consistently with previous studies showing a breed specific composition.
The rumen microbiota of grazing MA was characterized by a lower presence of Firmicutes and Patescibacteria. Both AU and MA grazing steers had a greater relative abundance of Fibrobacteres and Proteobacteria in the RL.This breed specific rumen microbiota composition had an influence on FAs and DMAs composition of rumen liquor. Grazing activity resulted in a significant increase of α-linolenic acid in the RL,
and therefore a decrease of the n3 /n6 ratio in the RL.
The FAs composition of the RL suggested an interesting result: that MA rumen BH process was less effective.
According to the results of the third trial, the AU and MA breed differed significantly due to the percentage of fibers: I and IIA were prevalent in the MA while the IIB fibers type were prevalent in AU.
The muscle fibers characterization of the two breed reported an interesting results confirmed also by the transcriptome analysis and bromatological characterization of the two muscles of the two breeds. Those evidence delineated a more oxidative fiber metabolism in the MA breed and a more glycolytic fibers metabolism in the AU breed.
The results of this experiment showed interesting differences between MA and AU steers and highlighted the importance of environmental and breeding conditions on the full expression of genotypic potential, in order to produce high quality beef.