Effect of alterations in closeup dietary neutral detergent fiber content on colostrum, transition, and mature milk production and composition in primiparous and multiparous Holstein dairy cattle.

There is limited research investigating the impact of closeup nutrition on colostrum and transition milk (TM) production and composition in both primiparous (PP) and multiparous (MP) cattle, despite the potential of alterations in prepartum metabolism to modify the availability of substrates for colostrum and milk synthesis. The objective of this study was to determine the effect of altering closeup dietary NDF content on colostrum, transition and mature milk composition and to characterize potential associations between cow and metabolic factors and colostrum yield and composition. Primiparous heifers were blocked by expected calving date and genetic parent average for milk yield and MP cows were blocked by parity, expected calving date, completed 305-d average milk yield and body condition score (BCS) at dry-off. From d -57 ± 5.8 before expected calving, PP (n = 20) and MP (n = 28) cattle were fed a high NDF diet (HI; 55.7% DM basis; 2.37 Mcal ME/kg DM). From d -19 ± 4.0, cattle were randomly assigned within block to a close-up diet (CUD) to either remain on HI or move to a low NDF diet (LO; 40.6% DM basis; 2.48 Mcal ME/kg DM). Blood samples were collected at wk -4, -3, -2, -1, at calving (within 12 h), and at d +4, +7, +14 and +21 relative to calving. Colostrum (milking [M] 1) was collected within 8 h of calving, followed by TM (M2 to M7) and mature milk (d 16 ± 2.0, wk +2), and total yield (kg) was measured at each milking. Component (fat, protein, lactose, TS, MUN, SCC, BHB), insulin, and immunoglobulin G (IgG) concentrations were analyzed by Fourier-Transform Infrared spectroscopy, ELISA, and radial immunodiffusion, respectively, and multiplied by milk yield at each respective milking to determine component (g), insulin (μg) and IgG (g) yields. Feeding LO had no effect on colostrum yield, component concentrations and yields, and IgG content and yield. However, cows fed LO had greater colostrum insulin concentration and yield, albeit this difference only existed between LO-MP and HI-MP cows and not between LO-PP and HI-PP heifers. The LO cows tended to have greater colostrum SCC than HI cows; yet, no differences were observed between parity with CUD. Interestingly, correlation analyses demonstrated that colostrum production was differentially associated with serum metabolites and hormones in PP heifers and MP cows. In terms of milk production, LO-MP cows produced greater transition and mature milk yields and component yields than HI-MP cows. In contrast, no differences existed between LO-PP and HI-PP heifers. In summary, the results suggest that colostral insulin levels and SCC are responsive to alterations in closeup NDF content. Further, providing low compared with high NDF diets during closeup improved transition and mature milk production in MP, but not PP, cattle, emphasizing the need for future research investigating the underlying differential metabolic and production responses to closeup dietary NDF content between parity groups.