Lag time from calving to first colostrum harvest in Holstein dairy cows: Association with colostral immunoglobulin G, volume, and dry matter.

The objective of this observational study was to describe the association between lag time from calving to first milking for colostrum harvest. Colostrum samples from primiparous and multiparous Holstein cows (n = 640) from a single herd milking approximately 5,200 cows 3 times daily in a 100-stall rotary parlor were used in this prospective cohort study. Calves were removed immediately after calving and not allowed to suckle their dam. Colostrum was harvested twice daily at 0930 and 1730 h and stored in a colostrum bank, from which all newborn calves were fed within 2 h after birth. Only cows milked at 0930 h were eligible for enrollment. Time of calving was recorded and time lag to the morning milking at 0930 h was calculated. Total yield of the colostrum was determined by weight. Colostrum samples were analyzed for IgG concentration by radial immunodiffusion and DM content by oven drying for 20 h at 100°C. Lag time in this cohort had a median of 10 h, ranged from 0 to 18 h, and was divided into 3 h increments to assess associations with outcomes of interest. Additionally, data were explored using segmented regression analyses. Total IgG yield was calculated from yield and IgG concentration. The association of colostral yield, IgG concentration, DM, as well as total IgG yield was analyzed for the different lag time groups using mixed effects linear regression. All lag time groups were compared with the control level 0 to 3 h using Dunnett's test. A total of 203 (31.7%), 149 (23.3%), 113 (17.7%), and 175 (27.3%) animals were in lactations 1, 2, 3, and ≥4, respectively. Cows were distributed with 78 (12.2%) in group 0 to 3 h, 116 (18.1%) in group >3 to 6 h, 96 (15%) in group >6 to 9 h, 123 (19.2%) in group >9 to 12 h, 110 (17.2%) in group >12 to 15 h, and 117 (18.3%) in the >15 to 18 h group. When lag time exceeded 9 h, the concentration of IgG and DM percentage were lower than in the 0 to 3 h control level. Colostrum yield was higher than the control level when cows were milked for the first time >15 h after calving. Segmented linear regression identified a breakpoint at 8.3 h for a decrease in IgG concentration and DM, as well as 5.7 h for an increase in yield. Lag time was not observed to be associated with total IgG yield in either model. After 9 h, a dilution effect was observed as demonstrated by a drop in IgG concentration and DM with no associated change in total IgG yield.