Abstract
Exposing Holstein dry cows to short-day photoperiod (SDPP) of 8 hours per day can improve milk production post-calving by 3.2 kg per day, compared with cows exposed to long-day photoperiod (LDPP) of 16 hours per day. Based on seasonal variations in colostrum quality and quantity, we hypothesized that altered photoperiod during the dry period also impacts colostrum production in dairy cows. Our objective was to study the effect of LD and SD during the dry period on colostrum production in Holstein and Jersey cows. Holstein and Jersey cows (n = 33) dried off 60 days before their due date were exposed to either SD (n = 9 Holstein, n = 8 Jersey) or LD (n = 8 Holstein, n = 8 Jersey) photoperiod at 18.3 °C until calving. Within 1 hour of calving, colostrum production was measured (kg), Brix score was determined and a milk sample was collected to evaluate composition (fat, protein, other solids, lactose, lactoferrin, somatic cell count) by DHIA and immunoglobulin content (IgA, IgG, IgG1, IgM) via ELISA. Data were analyzed with the PROC MIXED procedure of SAS 9.4 with fixed effects of breed and photoperiod treatment. Replicate, animal age, number of days of treatment, season of calving, inbreeding percentage and previous lactation production were included as random effects. Only the percentage of IgG made up by IgG1 differed by treatment, being greater for SDPP cows (79.6% ± 4.6%) than LDPP cows (68.0% ± 3.1%; P < 0.05). Jerseys had greater Brix score (27.8% ± 0.7% vs. 23.4% ± 0.7%), colostral protein (9.3% ± 0.3% vs. 7.6% ± 0.3%) and IgA (5.7 ± 0.7 vs. 3.2 ± 0.5 g/L; P < 0.01), and a tendency for fat and IgM to be greater as well (P < 0.10). These data indicate that measures of colostrum quantity and quality differ by breed but are largely unaffected by photoperiod treatment.