This study investigated the hypothesis that cattle fed to produce a lean carcass during a winter restriction period will subsequently grow faster and remain leaner than fatter steers during the summer, exploiting cheap grazed grass. Three studies were carried out; in the first study steers were restricted at three levels of growth (300, 600 and 900 g/day) during winter and turned out to graze grass during summer. At each level of growth during winter steers were fed on one of two diets aimed at producing steers of either a lean or fat carcass composition. At the end of the winter restriction period differences in lean composition were observed at the 300 and 600 g/day growth rates. Steers were slaughtered when they attained the target slaughter weight at the end of summer; but there was no difference between treatments in meat quality characteristics or fat composition. Liveweight gain during the summer period was inversely correlated to winter liveweight gain. Two further studies were carried out to assess the effect of altering carcass composition during winter, fed to a predicted growth rate of 600g/day to investigate the underlying physiological and endocrinological mechanism regulating the growth characteristics. In the first study at the end of winter steers that were fatter had higher glucose and insulin concentrations. No differences between diet treatments were detected in muscle protein synthesis or breakdown. At the end of the winter in the second experiment there were no differences in carcass composition, metabolite or hormone profiles between treatments. For both studies, at the end of summer, steers on different dietary treatments had similar carcass compositions and metabolic parameters. It was concluded that by altering the diet of steers during a winter restriction period the composition of carcass gain can be manipulated. Since steers altered the deposition of carcass protein and fat during the subsequent summer period at grass resulting in similar body compositions at slaughter it was deduced the that composition of steers at the end of winter remains unimportant. Reductions in beef production costs may be attained by restricting the growth rates during winter when commercial feeds are expensive.

Doctor of Philosophy / Department of Animal Sciences and Industry / Michael E. Dikeman / Sixty cull cows were utilized to investigate the effects of feeding a single or sequence of β-adrenergic agonists (β-AA) on performance, mRNA expression, carcass traits, economics, meat palatability, and ground beef color. Treatments included: 1) concentrate fed for 74 d (C); 2) concentrate fed for 49 d then supplemented with ractopamine-HCl for 25 d (RH); 3) concentrate fed for 51 d then supplemented with zilpaterol-HCl for 20 d (ZH); 4), concentrate fed for 26 d then supplemented with RH for 25 d followed by ZH for 20 d (RH + ZH). No differences existed among treatments for performance or carcass characteristics. However, cows supplemented with ZH (ZH and RH + ZH treatments) had increased LM areas (P = 0.18) compared to control and RH cows. Sequential feeding of RH followed by ZH had no influence on β2-adrenergic receptor (AR) mRNA expression. However, β2-AR mRNA was increased (P < 0.05) in the RH and ZH treatments when RH or ZH was supplemented during the last 20 to 25 d of feeding. Myosin heavy chain (MHC) Type IIa mRNA decreased (P < 0.05) from d 24 to 51 in all cows, while MHC-IIx increased (P < 0.05) in the ZH and RH + ZH treatments during ZH supplementation. No differences were observed in ground beef color shelf-life among treatments. Effects of β-AA supplementation on meat palatability varied among muscles. Infraspinatus steaks had improved (P < 0.05) WBSF values with β-AA supplementation. Psoas major steaks from the RH + ZH treatment were rated as more tender than steaks from all other treatments. Non-enhanced LM steaks from ZH supplemented cows had higher (P = 0.12) WBSF values along with decreased (P < 0.0001) percentages of degraded desmin compared to control and RH cows. Collagen solubility of the LM was increased with ZH supplementation compared to RH and control cows. Enhancement of steaks with 0.1 M calcium lactate improved LM tenderness of β-AA supplemented cows. Implanting and feeding cull cows for 74 d, regardless of β-AA supplementation, added value by transiting cows from a “cull” cow to “white” cow market.

Foram utilizados 24 cordeiros cruzados Ile de France, com peso médio inicial de 22,27 ± 1,85 kg e, aproximadamente, 80 dias de idade, suplementados com os níveis 0 (controle); 0,3; 0,9 e 2,7 g/kg de MS de produto enzimático comercial, contendo amilase, celulase, fitase, xilanase, betaglucanase, pectinase e protease, adicionado no momento da mistura do concentrado. O desempenho animal não foi afetado pela adição das enzimas, com médias de 37,3 ± 4,3 kg; 1,182 ± 0,153 kg/dia; 0,356 ± 0,077 kg/dia e 3,3 ± 0,3 para o PVF, IMS, GPD e CA, respectivamente. Para a digestibilidade da MS, FDN, FDA, PB, EE, NDT e amido, as médias foram, respectivamente, 80,55; 60,14; 58,80; 81,55; 52,02; 83,16 e 98,20%. A Digestibilidade da FDN apresentou uma tendência de aumento linear conforme o acréscimo do nível de enzima, com uma melhora de 11% para o último nível, em relação ao controle. As demais variáveis não foram alteradas. As concentrações de fósforo e glicose plasmáticos não foram alteradas pela enzima. O protozoário do gênero Entodinium sp. representou mais de 95% do total de ciliados para todos os tratamentos avaliados, e os dados se ajustaram ao efeito quadrático, com o nível de 2,18 kg de enzima/kg de MS proporcionando maior crescimento destes. Para o pH ruminal ao abate, não houve influência das enzimas. Os rendimentos de carcaça quente e fria apresentaram uma queda até os níveis de 1,61 e 1,55 g de enzima/kg de MS, respectivamente, sendo que, após estes valores, os rendimentos se aproximaram novamente do controle. A adição de níveis crescentes de enzimas diminuiu a perda de água por exsudação, mas não afetou a perda por cocção e a maciez da carne de cordeiros. Portanto, apesar da melhora em alguns parâmetros, o desempenho dos animais, bem como as características de carcaça e da carne, não foram afetados pela adição das enzimas, sendo que, para ovinos, o complexo enzimático avaliado não é eficaz sob as mesmas condições experimentais. / Twenty-four crossbred lambs Ile de France, with initial average body weight of 22,7 ± 1,85 kg and age of 80 days, were supplemented with 0 (control treatment); 0,3; 0,9 e 2,7 g/kg DM levels of enzymatic commercial product, with amylase, cellulose, phytase, xylanase, glucanase, pectinase e protease, added at the moment of concentrate mixing. Performance was not affected by enzyme complex supplement,, with averages of 37,3 ± 4,3 kg; 1,182 ± 0,153kg/day, 0,356 ± 0.077 kg/day and 3,3 ± 0,3 for FLW, DMI, ADG and FC, respectively. For DM, NDF, ADF, CP, EE, TDN and starch, the averages were, respectively, 80,55;60,14; 58,80; 81,55; 52,02; 83,16 and 98,20%. There was observed a tendency to FDN digestibility with linear increasing as the enzyme levels increased, with an improvement of 11% for the last level, compared to control diet. All the others variables were not changed. Glucose and phosphorus concentrations were not affected by the enzyme complex. The Entodinium sp. protozoa represented more than 95% of the total ciliated protozoa for all treatments studied and the data were adjusted by the quadratic effect, with the level of 2,18 kg of enzyme/kg of DM showing a better growing of those. Ruminal pH at the slaughter, was not affected by enzymes. Hot dressing percentage and cold dressing percentage decreased until levels of 1,61 and 1,55 g of enzyme/kg of DM, respectively, even when after these data, dressing percentage went back closely to the control treatment. The increasing levels addition of enzyme decreased drip loss, but did not affect the cocking loss and tenderness of lambs meat. Despite the improvement of some parameters, as well as performance, meat and carcass characteristics, were not affect by the enzymes, suggesting that enzyme complex analyzed was not efficient at the same experimental conditions for sheep.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The objective of this study was to evaluate the effect of three carbohydrate sources (corn, soybean hulls or wheat bran) in the diet on performance, carcass characteristics and meat and the components are not part of the carcass of steers finished on confinement. We used 24 steers, crossbred Charolais x Nellore, with initial age of 22 months of initial body weight 353.2 ± 10.6 kg. The animals were fed a diet with roughage: concentrate 40,2:59,8, and the volume consisting of sorghum silage. The daily intakes of DM and CP were not influenced by sources of carbohydrates. Animals fed soybean hulls had higher intake of NDF and ADF, whereas calves receiving corn consumed higher levels of NFC, and TDN ED. Animals fed corn or soybean hulls had greater weight gain and better feed conversion than steers receiving wheat bran. The slaughter weight was similar between the sources of carbohydrates, averaging 429.81; 433.18 and 430.46 kg for maize, soybean hulls and wheat bran, respectively. The weight cut sidecut was greater for steers fed corn diet compared with soybean hulls or wheat bran. The meat from the diet with soybean hulls had better flavor compared to the wheat bran. The loss of the cooking liquid and cholesterol content were higher in animals treated with maize as compared to those receiving soybean hulls or wheat bran. There was no effect of carbohydrate sources on the weights of vital organs and blood. The absolute and relative weights to the weight of empty body fat of the intestines and rumen were higher in animals fed with corn. The weight of the omasum was greater for the diet with wheat bran, while animals fed soybean hulls had higher absolute weight of kidney fat. / Objetivou-se neste estudo avaliar o efeito de três fontes de carboidratos (milho, casca de soja ou farelo de trigo) na dieta sobre o desempenho, as características da carcaça e da carne e dos componentes não integrantes da carcaça de novilhos de corte terminados em confinamento. Foram utilizados 24 novilhos castrados, mestiços Charolês x Nelore, com idade inicial de 22 meses e peso inicial de 353,2±10,6 kg. Os animais foram alimentados com dieta com relação volumoso:concentrado de 40,2:59,8, sendo o volumoso constituído de silagem de sorgo. Os consumos diários de MS e PB não foram influenciados pelas fontes de carboidratos. Animais alimentados com casca de soja apresentaram maiores ingestão de FDN e FDA, enquanto que os novilhos que receberam milho consumiram maiores teores de CNF, NDT e ED. Animais alimentados com milho ou casca de soja apresentaram maior ganho de peso e melhor conversão alimentar em relação aos novilhos que receberam farelo de trigo. O peso de abate foi similar entre as fontes de carboidratos, com médias de 429,81; 433,18 e 430,46 kg, para o milho, casca de soja e farelo de trigo, respectivamente. O peso do corte costilhar foi maior para os novilhos alimentados com milho em comparação a dieta com casca de soja ou farelo de trigo. A carne proveniente da dieta com casca de soja apresentou melhor palatabilidade em relação à do farelo de trigo. As perdas de líquidos à cocção e o conteúdo de colesterol foram maiores na carne dos animais tratados com milho em relação aos que receberam casca de soja ou farelo de trigo. Não houve efeito das fontes de carboidratos sobre os pesos dos órgãos vitais e de sangue. Os pesos absolutos e relativos ao peso de corpo vazio dos intestinos e da gordura ruminal foram maiores nos animais alimentados com milho. O peso de omaso foi maior para a dieta com farelo de trigo, enquanto que os animais alimentados com casca de soja apresentaram maior peso absoluto de gordura renal.

Foram utilizados 24 cordeiros cruzados Ile de France, com peso médio inicial de 22,27 ± 1,85 kg e, aproximadamente, 80 dias de idade, suplementados com os níveis 0 (controle); 0,3; 0,9 e 2,7 g/kg de MS de produto enzimático comercial, contendo amilase, celulase, fitase, xilanase, betaglucanase, pectinase e protease, adicionado no momento da mistura do concentrado. O desempenho animal não foi afetado pela adição das enzimas, com médias de 37,3 ± 4,3 kg; 1,182 ± 0,153 kg/dia; 0,356 ± 0,077 kg/dia e 3,3 ± 0,3 para o PVF, IMS, GPD e CA, respectivamente. Para a digestibilidade da MS, FDN, FDA, PB, EE, NDT e amido, as médias foram, respectivamente, 80,55; 60,14; 58,80; 81,55; 52,02; 83,16 e 98,20%. A Digestibilidade da FDN apresentou uma tendência de aumento linear conforme o acréscimo do nível de enzima, com uma melhora de 11% para o último nível, em relação ao controle. As demais variáveis não foram alteradas. As concentrações de fósforo e glicose plasmáticos não foram alteradas pela enzima. O protozoário do gênero Entodinium sp. representou mais de 95% do total de ciliados para todos os tratamentos avaliados, e os dados se ajustaram ao efeito quadrático, com o nível de 2,18 kg de enzima/kg de MS proporcionando maior crescimento destes. Para o pH ruminal ao abate, não houve influência das enzimas. Os rendimentos de carcaça quente e fria apresentaram uma queda até os níveis de 1,61 e 1,55 g de enzima/kg de MS, respectivamente, sendo que, após estes valores, os rendimentos se aproximaram novamente do controle. A adição de níveis crescentes de enzimas diminuiu a perda de água por exsudação, mas não afetou a perda por cocção e a maciez da carne de cordeiros. Portanto, apesar da melhora em alguns parâmetros, o desempenho dos animais, bem como as características de carcaça e da carne, não foram afetados pela adição das enzimas, sendo que, para ovinos, o complexo enzimático avaliado não é eficaz sob as mesmas condições experimentais. / Twenty-four crossbred lambs Ile de France, with initial average body weight of 22,7 ± 1,85 kg and age of 80 days, were supplemented with 0 (control treatment); 0,3; 0,9 e 2,7 g/kg DM levels of enzymatic commercial product, with amylase, cellulose, phytase, xylanase, glucanase, pectinase e protease, added at the moment of concentrate mixing. Performance was not affected by enzyme complex supplement,, with averages of 37,3 ± 4,3 kg; 1,182 ± 0,153kg/day, 0,356 ± 0.077 kg/day and 3,3 ± 0,3 for FLW, DMI, ADG and FC, respectively. For DM, NDF, ADF, CP, EE, TDN and starch, the averages were, respectively, 80,55;60,14; 58,80; 81,55; 52,02; 83,16 and 98,20%. There was observed a tendency to FDN digestibility with linear increasing as the enzyme levels increased, with an improvement of 11% for the last level, compared to control diet. All the others variables were not changed. Glucose and phosphorus concentrations were not affected by the enzyme complex. The Entodinium sp. protozoa represented more than 95% of the total ciliated protozoa for all treatments studied and the data were adjusted by the quadratic effect, with the level of 2,18 kg of enzyme/kg of DM showing a better growing of those. Ruminal pH at the slaughter, was not affected by enzymes. Hot dressing percentage and cold dressing percentage decreased until levels of 1,61 and 1,55 g of enzyme/kg of DM, respectively, even when after these data, dressing percentage went back closely to the control treatment. The increasing levels addition of enzyme decreased drip loss, but did not affect the cocking loss and tenderness of lambs meat. Despite the improvement of some parameters, as well as performance, meat and carcass characteristics, were not affect by the enzymes, suggesting that enzyme complex analyzed was not efficient at the same experimental conditions for sheep.