Storage of colostrum >4°C increases total bacterial count (TBC) which may compromise passive transfer of immunity. This experiment investigated the effect of colostrum stored at varying temperatures, to induce a difference in bacteria levels, on the rate of passive transfer of immunoglobulin G (IgG) in dairy heifer calves. Colostrum was collected immediately postpartum from Holstein-Friesian (HF) cows, tested for IgG concentration, and assigned to 1 of 5 treatments: (1) pasteurized, (2) fed when freshly collected, (3) stored at 4°C for ≥48 h (fridge), (4) stored at 13°C ≥48 h, and (5) stored at 22°C ≥48 h. Colostrum fed to each calf was tested for TBC, using serial dilution and IgG concentration using radial immunodiffusion (RID; Triple J Farms, WA). Seventy-five HF and HF × Jersey (JEX) heifer calves were removed from their dam and assigned to a treatment immediately postpartum at Teagasc Moorepark Research Farm, from 3 Feb to 25 Mar 2014. A randomized block design accounting for breed, birth date and birth weight (BW) was used. Calves were fed 8.5% of their BW in colostrum via stomach tube within 2 h. Calf blood samples were collected at 0 and 24 h of age and analyzed for IgG concentration using RID. Data were checked for normality and the MIXED procedure in SAS was used to examine the effect of treatment on serum IgG concentration. Pasteurised colostrum had a TBC <9,000 cfu/mL, fresh colostrum had 68,000 cfu/mL; both below the recommended level of 100,000 cfu/mL. Colostrum stored at 4°C had a TBC > 2 million cfu/mL, currently not recommended for feeding. Colostrum stored at 13°C and 22°C had significantly higher (P < 0.01) TBCs (>92 and >1000 million cfu/mL, respectively). Colostrum stored at 22°C had the lowest IgG concentration (62 g/L). The overall average colostrum IgG concentration across all treatments was 97 g/L. Zero-hour serum contained no IgG. Serum IgG of calves at 24 h from the pasteurised, fresh and 4°C treatments were similar, but were significantly higher (P < 0.05) than colostrum from the 13°C and 22°C treatments. Colostrum with high levels of bacteria reduced IgG absorption in dairy calves. Colostrum should be stored ≤ 4°C to minimize bacterial growth and improve subsequent passive transfer of IgG.