02477naa a2200361 a 450000100080000000500110000800800410001902400540006010000160011424500990013026000090022952014480023865000110168665000200169765000130171765000190173065000180174965300240176765300220179165300080181370000230182170000290184470000180187370000250189170000240191670000220194070000220196270000200198470000210200470000230202570000220204877300450207021560082023-08-21       2020    bl uuuu     u00u1 u    #d7 ahttps://doi.org/10.1016/j.livsci.2020.1040922DOI1 aMAIA, G. G.  aEffects of heat stress on rumination activity in Holstein-Gyr dry cows.h[electronic resource]  c2020  aThe objective of this study was to evaluate the effects of heat stress (HS) on: i) time and daily pattern of rumination and ii) 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. 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 a fistulated cow for 6, 24, 48 and 96 h. The RT was affected by HS (P&lt0.001) and time of the day (P&lt0.001). 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&lt0,05) and also in the slow-degradable fraction of concentrate (93.9% vs 85.1%, respectively; P&lt0,05). Finally, DMD of the diet reduced from 73% to 70% for animals exposed to HS compared to controls. In conclusion, HS negatively affected e rumination time and in situ ruminal degradability in dry dairy cows.  aBovino  aDigestibilidade  aGado Gir  aGado Holandês  aVaca Leiteira  aCâmara climatizada  aCinética ruminal  aTHI1 aSIQUEIRA, L. G. B.1 aVASCONCELOS, C. O. de P.1 aTOMICH, T. R.1 aCAMARGO, L. S. de A.1 aRODRIGUES, J. P. P.1 aMENEZES, R. A. de1 aGONÇALVES, L. C.1 aTEIXEIRA, B. F.1 aGRANDO, R. de O.1 aNOGUEIRA, L. A. G.1 aPEREIRA, L. G. R.  tLivestock Sciencegv. 239, 104092, 2020.