Twenty Dorper × Pelibuey primiparous ewes were used to evaluate effects of seasonal ambient heat stress (i.e., spring vs. summer) on physiological and metabolic responses under production conditions in an arid region. Ten ewes experiencing summer heat stress (i.e., temperature = 34.8 ± 4.6 °C; THI = 81.6 ± 3.2 units) and 10 under spring thermoneutral conditions (temperature = 24.2 ± 5.4 °C; THI = 68.0 ± 4.8 units) were corralled together to measure rectal temperature, respiratory frequency, and skin temperatures at 0600, 1200, 1800, and 2400 h on four occasions over 40 days. Blood metabolite and electrolyte concentrations were also measured at 0600 and 1800 hours. Data were analyzed with a completely randomized design using repeated measurements in time. Rectal and skin temperatures, as well as respiratory frequency, were higher (P < 0.01) in summer than spring at all measured days. Blood serum glucose, cholesterol, triglycerides, and chlorine concentrations were lower (P < 0.01) in summer than spring at 0800 and 1800 hours. In contrast, summer heat stress increased (P < 0.01) blood urea and potassium concentrations at 0800 and 1800 hours. Compared with spring thermoneutral conditions, summer heat stress affected the physiological and metabolic status of hair breed ewes in an arid region, which included blood metabolite and electrolyte adjustments to efficiently cope with summer heat stress.

The aim of this study was to evaluate effects of free ferulic acid (FA) supplementation on productive performance, some blood metabolite concentrations, and carcass characteristics of ewe lambs finished in a feedlot. Dorper×Pelibuey ewe lambs (n=20; BW=28.5±0.5 kg; age=5 mo) were individually housed in pens and assigned under a randomized complete block design to the following dietary treatments (n=10): daily feeding without (control) or with 300 mg of FA/animal. The feedlot feeding period lasted 34 d and then all ewe lambs were slaughtered. Free FA did not affect (P≥0.16) BW gain, ADG, DMI, and G:F during the first 17 d, but BW gain (P=0.10) and ADG (P=0.10) tended to decrease for FA from d 17 to 34 and from d 1 to 34 without affecting (P≥0.16) DMI and G:F in ewe lambs. Serum concentrations of glucose, cholesterol, triglyceride, total protein, and urea were not affected (P>0.05) by FA at d 1, 17, and 34 of the feeding period. Carcass characteristics were not affected (P>0.05) by FA. Stomach percentage tended (P=0.08) to decrease and leg yields increased (P=0.02) for FA. Other noncarcass components and wholesale cut yields were not affected (P>0.10) by FA. In conclusion, FA supplementation did not improve productive performance, metabolic status, and carcass characteristics of ewe lambs receiving a feedlot finishing diet.

Ten non-lactating multiparous Pelibuey breed ewes were housed in a corral to evaluate the effects of summer thermal stress on physiologic variables, estrous behavior, ovulation and corpus luteum functionality under natural conditions of an arid region. In summer and autumn, daily estrous detection with a ram fitted with an apron and blood sample collections were performed during two natural estrous cycles. An environment of heat stress was detected in summer and thermoneutral in autumn. Rectal temperature and respiratory frequency were greater (P < 0.01) in summer than in autumn during the morning and afternoon. Season did not affect (P > 0.05) live weight, body condition, length of estrous cycle or percentage of ewes in estrous and ovulating. Compared with autumn, serum progesterone concentrations in summer decreased (P < 0.05) between days 8 and 14 of the estrous cycle. It is concluded that under outdoor conditions of arid regions, while estrous and ovulatory activities of Pelibuey ewes were not affected by summer thermal stress, the corpus luteum functionality was decreased.

Estrés calórico. Respuestas productivas. ADDITIONAL KEYWORDSHeat stress. Productive performance. RESUMENSe determinó el efecto combinado de aumentar la frecuencia de alimentación e iluminación nocturna durante el verano en la respuesta productiva y características de la canal de 171 vaquillas de razas de carne. Los tratamientos fueron: dos raciones diarias (testigo) y tres raciones diarias más la iluminación del comedero de 12:00 a 02:00 h (tratado), durante 84 días. Las vaquillas recibieron las mismas dietas. Las vaquillas tratadas pesaron 16 kg más (p<0,05), tuvieron mayor ganancia diaria (0,140 kg d -1 ; p<0,05), y menor conversión alimenticia (7,69 vs. 8,69 kg; p<0,10) que el grupo testigo, pero el consumo de alimento no fue diferente. Las vaquillas testigo mostraron mayor (p<0,05) frecuencia respiratoria que las tratadas (93,5 vs. 83,9 resp min -1 ), lo que sugiere un mayor grado de estrés calórico en esos animales. El peso de la canal caliente fue mayor (p<0,05) en las vaquillas tratadas que en las testigo (244,3 vs. 233,9 kg), pero no hubo diferencias en otras características de la canal. Los resultados sugieren que el aumentar la frecuencia de alimentación y el fotoperiodo en verano pueden mejorar las respuestas productivas y la adaptación a temperaturas altas en vaquillas engordadas en corral. SUMMARYThe combined effect of increasing feeding frequency and night lighting on feedlot performance and carcass traits during summer was studied in 171 beef heifers. Treatments were: two rations daily (control group) and three rations daily (treated group), during a feedlot period of 84 days. Heifers received the same diets. Treated heifers were 16 kg heavier (p<0.05), had higher daily gain (0.140 kg d -1 ; p<0.05), and better feed conversion (7.69 vs. 8.69 dg d -1 ; p<0.05) than control heifers, although feed intake was similar. Control heifers showed higher (p<0.05) respiration rate than treated (93.5 vs. 83.9 breaths min -1 ), which suggests higher level of heat stress in those animals. Hot carcass weight was higher (p<0.05) in treated heifers than in control (244.3 vs. 233.9 kg); however, there were no differences in the other carcass traits. These results suggest that increasing feeding frequency and photoperiod during summer may improve feedlot performance and adaptation to high temperatures in beef heifers. INTRODUCCIÓNEl noroeste de México, se caracteriza por la engorda intensiva de bovinos en corral ya que la intensa actividad agrícola regional permite disponer de forraje, cereales, esquilmos agrícolas y subproductos industriales para consumo animal (Walther, 1996). Esta zona es desértica y el estrés por calor es un punto crítico porque puede causar pérdidas importantes debido a la disminución del consumo de alimento y al gasto energético adicional para mantener la

Se determinó el efecto combinado de aumentar la frecuencia de alimentación e iluminación nocturna durante el verano en la respuesta productiva y características de la canal de 171 vaquillas de razas de carne. Los tratamientos fueron: dos raciones diarias (testigo) y tres raciones diarias más la iluminación del comedero de 12:00 a 02:00 h (tratado), durante 84 días. Las vaquillas recibieron las mismas dietas. Las vaquillas tratadas pesaron 16 kg más (p