نبذة مختصرة : This study aims to explore the economical and suitable bedding replacement frequency for calves in winter in northwest China. The optimal bedding replacement frequency was determined to evaluate the concentrations of ammonia and carbon dioxide in a calf barn, the growth performance, behavior, and serum biochemistry of the calf in winter. The experiment was selected as 15 angus calves about 25 days of age with an average body weight of (39.73 ± 2.38) kg, and then completely randomly divided into three treatments, each of which was three replicates (2, 2, or 1 calves calf per replicate). Specifically, the bedding was replaced every two days (the Maximum replacement frequency, MAX), four days (the Medium replacement frequency, MED), or eight days (the minimum replacement frequency, MIN). The duration of the experiment was 24 days. Before that, 31.5 kg of clean straw was evenly laid in each calf pen, where the thickness of the bedding was 10 cm. The bedding material was replaced at 15:00 every day, according to the experimental design. The results showed that there was no significant difference in the carbon dioxide concentration among the three treatments. The daily average concentrations of ammonia in the MAX and MED group groups were (0.26±0.07) and (0.37±0.03) mg/m3, respectively, which were significantly lower than the (0.64±0.07) mg/m3 in the MIN group. It infers that the increased frequency of bedding replacement led to the better air quality in the calf barn. The average values of daily weight gain were (0.70±0.09), (0.71±0.18), and (0.58±0.12) in the MAX, MED, and MIN groupgroups, respectively. Therefore, there was also a significant upward trend in the average daily weight gain of the MAX and MED groupgroups, compared with the MIN group. Besides, the surface dirt scores of the calves in the MAX and MED group groups were 1.16±0.06 and 1.74±0.06, respectively, which were significantly lower than the 2.11±0.05 of the MIN group. The diarrhea rate of the MAX and MED groups were was significantly lower than that of the MIN group. In addition, the payment of bedding management was calculated using 30 days per month, including the bedding material and labor costs. It was found that the input of bedding, the labor cost, and the total were 1 434.5, 9 000, and was 10 434.5 RMB per month. In the MED group, the cost of bedding, labor, and the total cost were 717.3, 6 000, and 6 717.3 RMB per month. In the MIN group, those were 358.6, 3 000, and 3 358.6 RMB per month. The monthly cost in the MAX group was 1.55 times that in the MED group, and 3.11 times that in the MIN group. The monthly cost of the MED group was 2.00 times that of the MIN group. In conclusion, an optimal combination was achieved under the condition of stocking density of 4.5-9 m2/head, updating bedding every four days (MED group) in the winter bedding management of calves in the northern China. In this case, the body surface can be kept the clean of for calves, thereby to reducereducing the diarrhea rate for the better growth performance of calves. The more suitable cost input was obtained to fully meet the two-way needs of calf welfare and breeding efficiency. [ABSTRACT FROM AUTHOR]
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