Effects of alterations in close-up dietary neutral detergent fiber content on colostrum and transition and mature milk production and composition in primiparous and multiparous Holstein dairy cattle.

There is a lack of knowledge pertaining to the pre-calving optimization of colostrum and transmission milk (TM) synthesis and, consequently, calf development and health. It is well known that altering pre-calving dietary neutral detergent fibre (NDF) content, and therefore energy supply, can influence both cow metabolic factors, including pre-calving dry matter intake (DMI), mobilization of adipose stores, insulin, and energy status. As such, sufficient information exists pertaining to the effects of pre-calving cow metabolic factors on milk production during established lactation; however, potential relationships between alterations in such factors and colostrum production is yet to be fully elucidated. Alterations in close-up dietary energy supply consistently have no effect on colostrum yield, its effect on colostrum IgG remains conflicting. Also, how altering close-up energy supply may influence dam metabolism and the pre-calving udder synthesis of colostrum bioactive compounds, such as insulin, in heifers is largely unknown. This may differ from that of cows due to differences in the metabolic response to high-energy pre-calving diets and their increased requirements for growth and udder development. Furthermore, the mechanism by which increasing close-up dietary energy and subsequent changes in dam metabolism may alter TM yield and composition in both heifers and cows has yet to be elucidated. Thus, it was hypothesized by the authors cited, that altering close-up dietary NDF content, and consequently energy supply, would influence production and composition of colostrum and transition and mature milk, and that such alterations would be associated with cow-level and metabolic factors. Thus, the objectives of their study were to use Holstein heifers and cows to determine (1) the effects of altering close-up dietary NDF content on production of colostrum and transition and mature milk and (2) how pre-calving metabolic factors, including serum energy metabolites and hormones, and cow-level factors, including DMI, BW, and BCS, may affect colostrum production.

Twenty heifers were blocked by expected calving date and genetic parent average for milk yield, and 28 cows were blocked by lactation number, expected calving date, completed 305-day average milk yield and BCS at dry-off. From day −57 ± 5.8 before expected calving, the heifers and cows were fed a high-NDF (HI) diet (55.7% on DM basis; 2.37 Mcal ME/kg DM). From day −19 ± 4.0, the heifers and cows were randomly assigned within block to a close-up diet (CUD) to either remain on HI or move to a low-NDF (LO) diet (40.6% on DM basis; 2.48 Mcal ME/kg DM). Blood samples were collected at week −4, −3, −2, and −1, at calving (within 12 hours), and at day +4, +7, +14, and +21 relative to calving. Colostrum (milking [M] 1) was collected within 8 hours of calving, followed by TM (M2–M7) and mature milk (day 16 ± 2.0, weeks +2), and total yield (kg) was measured at each milking. Component (fat, protein, lactose, TS, MUN, SCC, β-hydroxibuterate [BHB]), insulin, and immunoglobulin G [IgG] concentrations were analysed 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 the LO diet had no effect on colostrum yield, component concentrations and yields, and IgG content and yield. However, the heifers and cows fed the LO diet had greater colostrum insulin concentration and yield, albeit this difference only existed between LO and HI cows and not between LO and HI heifers. The LO animals tended to have greater colostrum SCC than HI animals; however, no differences were observed between heifers and cows with CUD. Correlation analyses demonstrated that colostrum production was differentially associated with serum metabolites and hormones in heifers and cows. In terms of milk production, LO-C produced greater transition and mature milk yields and component yields than HI-C. In contrast, no differences in transition or mature milk production existed between heifers fed LO and HI.

Interpretive summary: Colostrum yield and IgG content and yield were not responsive to close-up dietary NDF content; yet, the bioactive fraction, namely colostrum insulin and SCC, increased in response to decreased close-up dietary NDF content. The availability of serum glucose at calving appeared to be of importance to colostrum IgG and component output in heifers while colostrum production in cows appeared to have a greater reliance on metabolic signals. The cows fed a low NDF CUD had greater transition and mature milk yield and yields of milk components compared to cows fed a high NDF CUD, whereas production responses were not observed in heifers fed differing levels of CUD NDF content in the present study. Collectively, these results suggest that close-up dietary NDF content may provide a modifiable strategy to alter the bioactive fraction of colostrum despite colostrum production potentially being differentially regulated in heifers compared to cows.