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To rear lambs of the Ojalada breed, fed exclusively on mothers’ milk until 5 weeks, three feeding systems were compared: a) ewes kept indoors and fed chopped straw plus concentrate (IND+CH+C), total mixed ration (TMR); b) ewes kept indoors and fed whole straw in the form of large bales plus concentrate (IND+W+C), TMR; and c) free-range grazing plus concentrate (GR+C; control group). Parameters related to ruminal fermentation (pH, NH 3 -N concentration and proportion of volatile fatty acids (VFAs)) in 40 sheep during a production cycle were monitored. The plasma concentrations of stress-related metabolites (i.e., glucose, lactate, phosphate, creatine kinase (CK), cortisol and non-esterified fatty acids (NEFAs)) during a production cycle and in 10 sheep during lactation (5 weeks) were tested. The sheep fed a whole forage ration (IND+W+C and GR+C treatment group) had higher concentrations of NH 3 -N and total VFAs, but no differences were found in the acetate/propionate ratio in sheep in the IND+CH+C treatment group compared to the control group. When analyzing plasma metabolites, we found that during the entire production cycle, grazing sheep had higher concentrations of glucose and cortisol. The concentration of NEFAs was also higher for the GR+C treatment group when evaluated during lactation. Thus, we concluded that the ration particle size for sheep fed a TMR influences the concentration of NH 3 -N and VFAs in the rumen. Keeping the sheep indoors during the production cycle and during lactation did not increase the plasma levels of the evaluated stress indicators. Para producir corderos de raza Ojalada, alimentados hasta las 5 semanas unicamente con leche de la madre, se compararon tres sistemas de alimentacion: a) ovejas estabuladas y alimentadas con paja molida suplementada con concentrado preparado y distribuido mecanicamente (IND+CH+C), racion integral; b) ovejas estabuladas y alimentadas con grandes pacas de paja suplementada con concentrado (IND+W+C), racion integral; y c) ovejas en pastoreo suplementadas con concentrado (GR+C), grupo control. Se controlaron algunos parametros relacionados con la fermentacion ruminal (pH, NH 3 -N, acidos grasos volatiles) en 40 ovejas durante un ciclo productivo, y la concentracion en plasma de algunos metabolitos relacionados con el estres (glucosa, lactato, creatinina fosfato, cortisol y acidos grasos no esterificados (NEFAs)) en un ciclo productivo y tambien en 10 ovejas durante la fase de lactacion (5 semanas). Las ovejas alimentadas con una racion con forraje entero (IND+W+C y GR+C) presentaron mayor contenido en NH 3 -N y mayor contenido total de acidos grasos volatiles (VFA), aunque en ningun caso se encontraron diferencias en el ratio acetato/propionato con las ovejas del tratamiento IND+CH+C. Se encontro para todo el ciclo productivo que las ovejas en pastoreo tuvieron mayor concentracion de glucosa y cortisol, siendo tambien superior para este tratamiento la concentracion de NEFAs cuando se evalua el periodo de lactacion. El tamano de particula en las raciones de ovejas alimentadas con una racion unica y mecanizada influye en la concentracion de NH 3 -N y VFA del rumen, aunque el mantenerlas cerradas durante un ciclo productivo y durante el periodo de lactacion, no incremento el contenido en plasma de los indicadores de estres evaluados. |
