Development of ruminating behavior in Holstein calves between birth and 30 days of age.

Ruminating behavior accompanies the development of the rumen and the intake of solid feed in calves. However, few studies have reported on the emergence and development of rumination. In this study, we observed ruminating behavior changes of 56 Holstein calves (body weight at birth = 40.1 ± 3.96 kg; mean ± standard deviation) from birth to 30 d of age under the feeding management of suckling calves that were only fed pelleted concentrate feed and milk. All calves were housed in individual pens equipped with infrared cameras. We explored feed intake within 30 d of age, body weight on 61 d of age, and other apparent indicators, including the age of first eating the bedding, duration of non-nutritive oral behavior at 25 and 30 d of age, total starter feed intake within 30 d of age, average daily starter feed intake within 30 d of age, and duration of ruminating behavior at 25 and 30 d of age for all calves, to further explore the effects of the age of first ruminating behavior (AFR). The AFR fitted the normal distribution and ranged from 15 to 20 d of age for 50% of the experimental population. The AFR was positively correlated with the age of first eating the bedding and duration of non-nutritive oral behavior at 30 d of age. Total starter feed intake within 30 d of age, average daily starter feed intake within 30 d of age, duration of ruminating behavior at 25 and 30 d of age, and duration of eating the bedding at 25 and 30 d of age were negatively correlated with AFR. Overall, to the best of our knowledge, this is the first study that has analyzed the correlation between AFR and other indicators. We found that earlier AFR was associated with shorter duration of non-nutritive oral behavior, longer durations of rumination and eating the bedding, and higher feed intake by 30 d of age.