부산대학교 도서관

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) respiration rate (77.5 vs 83.7 breaths/min) and rectal temperature (39.1 vs 39.3 °C) in the afternoon, than non-cooled (control) cows. Serum thyroxin and triiodothyronine levels were higher (P<0.05) in cooled cows than in non-cooled cows (38.0 vs 30.2 ng/ml and 0.857 vs 0.681 ng/ml, respectively). Calf birth weight showed only a numerical trend to be higher (P=0.421) in cooled cows (35.7 vs 32.9). Milk production showed a tendency (P=0.144) to be higher in the cooled (28.1 kg) than in the non-cooled group (25.2 kg), while fat content (P<0.05) was greater in the cooled (3.2 %) than in the non-cooled group (2.9 %); therefore, average fat-corrected milk production at week eight postpartum was higher (P<0.01) for the cooled group (28.6 vs 25.7 kg) compared to control. However, milk production and protein percent were similar (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. [ABSTRACT FROM AUTHOR]