A note on rumination behavior of dairy cows under intensive grazing systems

Rumination is an important aspect of rumen function and animal welfare. However, there is a paucity of information regarding rumination behavior and diurnal patterns among grazing dairy cows of different breeds, genetic merits and ages managed under intensive grazing systems. An observational study was conducted to explore these potential associations and highlight possible behavioral adaptations to compensate for variations in rumination time. Three hundred and twenty lactating dairy cows were fitted with HR Tag™ rumination collars from day 30 to day 240 in milk (DIM), to record daily rumination activity (min per day and min every 2 h), mastication rhythm (seconds between ruminative chews) and interval between regurgitation of bolus (s). The group of cows consisted of a mix of two breeds (Friesian and Jersey) and their crossbreeds (Friesian12×Jersey4 and Friesian8×Jersey8) with ages of 2 (heifers), 3 and older than 4 yr old. The results indicate no relationships among age, breed, genetic merit and daily rumination time, but a differential diurnal pattern of rumination activity. Age and breed were also associated with mastication rhythm and interval between regurgitation of bolus. The older the cow and the greater the Friesian pedigree, the larger the interval between rumination chews. The total number and time of mastications per bolus appeared to increase with cow age. Increments in Friesian pedigree were associated with fewer regurgitations of bolus per day, a longer time of mastication per bolus and more chews per bolus. The number of regurgitations of bolus per day decreased with the age of the cow. If daily rumination time is controlled by feeding management, these associations possibly highlight underlying compensatory mechanisms, for example to reductions of chewing efficiency as cows age. Therefore, specific feeding managements to manipulate rumination behavior could be designed based on age and breed. Due to the observational nature of the present study, results should be interpreted with caution. At the same time, such observations open up challenging questions for future controlled and detailed experiments.