Rumination Time in Relation to Reproductive Status in Lactating Dairy Cows Fed Partial Mixed Ration Based on Corn Silage

The objective of this study was to characterize the rumination time in lactating dairy cows fed with corn silage. Rumination time was recorded 24 h/day using direct visual observation. Six trials were conducted during 2018, 2019 and 2020, and rumination time was recorded in 480-2-hour periods from 40 Holstein Friesian cows. In each trial, 6 or 8 cows were selected and balanced for days in milk (DIM), milk production and number of lactations.Each cow was recorded continuously for periods of 2 h at a time to complete a full 24-h period per week (12 values per day). Data from all cows were associated with 4 reproductive statuses of cows: Inseminated (1-45 days after insemination), Open (45-150 days after calving), not-pregnant and pregnant. The longest rumination time (RT) was found in pregnant cows (average 536.9 ± 29.87 min/day), and the shortest RT was in open cows (average 420.3 ± 63.2 min/day). Inseminated and non-pregnant cows were found with intermediate values (527.3 ± 82.4 min/day and 467.1 ± 30.7 respectively). Significantly different RT means were found between pregnant and open cows (p< 0.0001), pregnant vs. inseminated cows (p<0.0001), and between inseminated and open cows (p=0.0005). We concluded that some gynecological conditions of lactating cows affect the RT. Measurement of RT by visual observations proved to be acceptable for the conditions of this study when cows were housed indoors and were fed withpartial mixed ration (PMR) based on corn silage.