Leonel Avendaño Reyes

Evaluación de un sistema de enfriamiento aplicado en el periodo seco de ganado lechero durante el verano

In order to determine some physiological responses 60 d prepartum and production responses postpartum to a cooling system in summer, 24 multiparous Holstein cows were allocated to two groups: one group with (n=12) and a second group without (n=12) cooling. Cooled cows showed a lower (P 0.05). Reproductively, only total conception rate was higher (P<0.05) in cooled cows than in non-cooled cows (100 vs 63.6 %). Non-cooled cows showed a 42 % culling rate, while no cow was culled in the cooled group (P<0.05). An economic analysis showed a net profit of 75 dollars cow/year for the cooling system. Results show that cooling dry cows reduce heat stress, that resulted in higher fat-corrected milk and milk fat production in the subsequent lactation and in higher economical benefits for dairy producers.

Respuesta fisiológica y productiva de novillos engordados con un sistema de enfriamiento a espacio abierto en un clima árido y seco

Evaluation of the effects of an open space cooling system on weight gain, respiration rate and serum thyroid hormone (T3 and T4) levels in feedlot steers was done using 60 Holstein steers (344 kg) allotted randomly in two treatments: a control with only shade in the corral (n=30), and a cooling with an open space cooling system (n=30). Daily maximum temperature-humidity index (THI) ranged from 82 to 88 during the 12-week study period. The open space cooling system consisted of a fan with 2.4 m diameter blade that displaced 1,416 m3 of air per minute and had a 90o oscillation range, and sprinklers. The fan was installed at 8 m distance on the south side of the shade. Water discharge was 12 L per minute over a 7 h period. Body weight and thyroid hormone levels were measured every two weeks and respiration rate twice a week (1400). Data were analyzed by repeated measures, including initial weight as a covariate. Daily weight gain was different (P<0.05) between the cooling treatment (1.43±0.091 kg/d) and the control treatment (1.25±0.091 kg/d). Respiration rate was lower (P<0.05) in steers in the cooling treatment (94±0.74 breaths per minute) than in those in the control treatment (111±0.74 breaths per minute). Levels of T3 were higher (P<0.05) in the cooling treatment (1.7±0.042) than in the control (1.5±0.042). Levels of T4 were similar between the cooling (79.3±1.82 ng/ml) and control (78.2±1.82 ng/ml) treatments. Use of this cooling system improved production performance and comfort in feedlot Holstein steers in a hot, dry climate.