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Effects of heat stress on rumination activity and ruminal in situ degradability in dairy cows.

L. G. R. Pereira



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Effects of heat stress on rumination activity and ruminal in situ degradability in dairy cows.
G. G. Maia1, L. G. B. Siqueira2, C. O. P. Vasconcelos1, T. R. Tomich2, L. S. A. Camargo2, J. P. P. Rodrigues3, R. A. Menezes4, L. C. Gon�alves4, B. F. Teixeira5, R. O. Grando5, L. A. G. Nogueira1, L. G. R. Pereira*2. 1Universidade Federal Fluminense Niter�i, RJ, Brazil, 2Empresa Brasileira de Pesquisa Agropecu�ria - Embrapa Juiz de Fora, MG, Brazil, 3Universidade Federal do Sul e Sudeste do Par� Xinguara, PA, Brazil, 4Universidade Federal de Minas Belo Horizonte, MG, Brazil, 5Instituto de Desenvolvimento do Alto Uruguai Get�lio Vargas, RS, Brazil.

The objective of this study was to evaluate the effects of heat stress (HS) on (1) time and daily pattern of rumination, and (2) in situ degradability in Holstein-Gyr crossbred dry cows. Nine cows, weighing 556.2 � 97.1 kg were housed in a climate chamber (average THI = 83.1) or a freestall barn (average THI = 66.5) randomly assigned to treatments in a crossover design. For each animal, there were 25 d of data collection in each treatment. Rumination and intake patterns at different days or 2-h periods were evaluated using the MIXED procedure. Cows were fed corn silage ad libitum and 1 kg of concentrate as a maintenance diet. To measure rumination, we used a sensor attached to a collar. The in situ ruminal degradability was evaluated by incubation of concentrate, silage, and diet samples into the rumen of one fistulated cow for 6, 24, 48 and 96 h when this cow was under HS (climate chamber) and at the freestall (control) after 21 d of the starting of the treatment. The ruminal degradability kinetics were estimated using a uni-compartmental model with the Marquardt algorithm to fit nonlinear regression. The RT was affected by HS (P < 0.001) and time of the day (P < 0.001). The rumination pattern for control and HS cows had a first peak at approximately 04:00h and the magnitude of this peak in HS was 22.9% less than controls. The second RT peak occurred in the evening (~20:00h), when RT in HS was 27.8% less compared with controls. We observed a reduction in dry matter digestibility (DMD) of concentrate (85.1% vs 77.8%, control and HS, respectively; P < 0,05) and also in the slow-degradable fraction of concentrate (93.9% vs 85.1%, respectively; P < 0,05). Finally, DMD of the diet reduced from 73% to 70% for animals exposed to HS compared with controls. In conclusion, HS negatively affected the rumination time and in situ ruminal degradability in dry dairy cows.

Keywords: climate chamber, precision dairy farming, sensors.