Abstract
Uruguay is a primary meat exporter being the 7th country in the world in volume, on which its economy is highly dependent. Meat production systems are mainly based on rangeland pastures but during the last years, international meat prices and the opening of new markets have provoked the intensification of fattening systems in order to improve animal performance and carcass and meat quality traits. These intensive systems include a wide range of feeding alternatives between pasture and concentrate utilization. This could involve many differences in terms of carcass and meat quality, which require to be studied. The challenge is to produce a finishing strategy to improve the product, without modifying the peculiar characteristics acquired during extensive grazing conditions (low-cost production and healthy meat for human consumption), and without compromising neither animal welfare nor the environment. Therefore, the objective of the present thesis work was to evaluate the effect of these emerging finishing systems and different pre slaughter procedures on animal welfare, and its effects on meat quality. Two experiments were conducted in Uruguay during 2005-2006 and 2006-2007, respectively. In the first experiment, eighty four Hereford steers were randomly assigned to four diets with increasing levels of grain, from an artificial prairie without supplement to a feed lot system on the basis of concentrate and hay. Live weight gains increased with the level of energy in the diet determining different slaughter dates for all treatments. Animals with higher temperament had higher ADG regardless of diet. According to physiological indicators, confined animals had higher difficulties to get used to the productive conditions. These difficulties could have been due to deprivation of performing relevant behaviours, to crowding and/or due to animal impossibility to face bad weather conditions. Steers from the feed lot had a higher incidence of diet diseases as well as a higher mortality rate. We could infer that the well-being of these animals was lower during the finishing period. Intermediate treatments had higher hot carcass weight and valuable cuts weight, but there were no differences in retail cut yields, between treatments. There were no differences in muscle proportion in the pistola cut between the different finishing strategies, but fat percentage was higher in those treatments with higher level of grain in the diet. Pasture fed animals showed higher fat b values, decreasing with the level of energy in the diet. No differences were found in meat colour between pasture based finishing treatments, but all of them had more red meat than the feed lot. Shear force values were higher in the feed lot system after 7 and 20 days of aging. Calmer animals produced lower shear force values, regardless of finishing strategy.  
In the second experiment, 30 Hereford and 30 Braford steers were assigned to two finishing diets: a) native pasture with corn grain as supplement and b) a high quality pasture without supplementation. ADG did not differ between diets. Calmer animals had higher ADG regardless of diet or breed. Considering ADG, health status and mortality rate, we could preliminary infer that well being was not affected in any diet, during the finishing period. In this experiment, two lairage periods were also evaluated (3 and 15 hours). Calmer animals showed a lower stress response after the different pre slaughter stages (transport, lairage, management and stunning procedure). Transportation did not provoke an emotional stress response, suggesting that its negative effect on animal well being, could be minimised through the implementation of good management practices. All animals showed a physical stress response after lairage, being higher in overnight steers. However, animals from that group had the opportunity to rest during the night and to physically recover. Those animals had a better rate of pH decrease and consequently, lower shear force values. All animals were excited during the first hour in lairage, showing a high frequency of negative behaviours, but animals from the short lairage group did not have the opportunity to rest and to get calm before slaughter. All animals had an important rise in HPA activity in the preslaughter moment, suggesting an emotional stress state that should be deeply studied. A pre slaughter period of 3 hours in the abattoir seemed not to be enough from both perspectives (welfare and meat quality). Supplemented animals had higher hot carcass and valuable cuts weight, but there were no differences in retail cut yield, between diets. There were no differenes in pistola muscle proportion between diets, but pistola fat percentage and subcutaneous fat thickness were also higher in the supplemented animals. No differences were registered in shear force values between finishing strategies, but as it was previously mentioned, pH decrease was better in the 15 hours group with the consequent positive effects on meat tenderness. Braford animals had higher ADG during the experiment, higher muscle percentage in the pistola cut, higher valuable cuts weight and a higher meat yield (7CY and RLY). However, they were more excitable and had higher shear force values than Hereford steers.
From both experiments we concluded that temperament could be a very important tool regarding its effects on productivity and meat quality, regardless of finishing strategy or animal breed. The inclusion of increasing levels of grain in the diet until 1.2 % of live weight, could improve animal performance without affecting animal well-being, provided that preventive strict measures are taken in relation to diet problems and diseases. The confined system improved productivity but animals were more stressed, health was compromised and a higher mortality rate was registered. Moreover, meat quality was affected. Regarding  to lairage duration, it was considered that animals should have a resting time pre slaughter (higher than 3 hours and probably lower than 15 hours) in order to rest and get calm, probably recovering muscle glycogen contents with the desirable higher meat quality.