The aim of this study was to investigate the effect of different BCS and reducing the length of dry period in Holstein dairy cows on performance, metabolism and health indicators of neonatal calves. For this purpose, 64 multiparous pregnant cows based on BCS and length of dry period were assigned to 1 of 4 treatment groups in a 2 × 2 factorial design (16 cows in each treatment). The treatments included 1) cows with medium BCS (MBCS, 2.75-3.25) and short dry period (SDP, 30 days); 2) cows with high BCS (HBCS, 3.4-5) and SDP; 3) cows with MBCS (2.75-3.25) and long dry period (LDP, 56 days), (4) cows with HBCS (3.4-5) and LDP. Blood samples of cows were collected at calving and blood samples of calves were taken at 1, 14, 28 and 42 days of age for serological analysis. Also, whole blood and fecal samples were taken at day 14 for complete blood count test and total microbial count, respectively. Fecal score and rectal temperature were measured daily, starter intake and BW were measured weekly and skeletal growth parameters were measured on day 0 and 63 of age. Cows with SDP had longer pregnancy period than those with LDP (P 0.05). Calves that born from cows with SDP and MBCS had greater birth weight (P 0.05) and final BW (P = 0.07) than the other treatments. Calves that born from cows with SDP had lower concentration of NEFA (P = 0.08), BHBA (P 0.05), and higher concentration of protein and albumin (P 0.05) than those born from cows with LDP. highest concentration of AST (P 0.05) and lowest T4 (P 0.01) belonged to calves born of mothers with a traditional dry period and high BCS. There was a positive correlation between NEFA (P 0.01, r = 0.69) and BHBA (P 0.01, r = 0.52) concentration of cows and their calves at calving day. The neutrophil to lymphocyte ratio (P 0.05), fecal E. coli (P 0.05) and the number of days with diarrhea were greater in calves that born from cows with HBCS than those born from cows with MBCS. Therefore, the results of this experiment showed that the best performance and health indexes of neonatal calves were obtained when dairy cows experienced short dry period and medium BCS. Keywords: Dry period, BCS, Pregnancy Length, Health Indicators, neonatal Calves
