Lorenzo Enrique Hernández-Castellano

This study investigated the relationship between Brix values and the nutritional and immunological composition of bovine colostrum. Colostrum samples (n = 82) were collected from Holstein-Friesian cows on four dairy farms. Dry matter (DM), solids non-fat (SNF), crude protein (CP), fat, IgG concentrations, and Brix values were determined. Correlation, regression, and receiver operating characteristic (ROC) analyses were used to evaluate associations among variables and identify a Brix cut-off for high-quality colostrum (IgG ≥ 50 g/L). Brix was positively associated with both CP (ρ = 0.90) and IgG concentration (ρ = 0.75), although the relationship between Brix and IgG was significantly influenced by the IgG/CP ratio. A robust regression model including SNF and fat provided the best prediction of Brix values (R² = 0.98). ROC analysis identified a Brix cut-off of approximately 25%, which detected high-quality colostrum with 83% sensitivity and 76% specificity. Colostrum above this threshold had higher DM, SNF, CP, and IgG concentrations, but not fat concentration. These findings suggest that Brix values primarily reflect the soluble solids fraction of colostrum and that variation in the proportion of IgG within total protein may contribute to the variability in Brix–IgG relationships and threshold values reported among studies.

This study hypothesises that a high‐starch (HS) diet during the last month of gestation enhances colostrum yield and composition as well as the dam and goat kid metabolism, immune status and performance. Thirty multiparous and pregnant Majorera dairy goats were randomly assigned to a prepartum dietary treatment (CON vs. HS) on wk −4 relative to the expected parturition. Goats were fed either a control ( n = 15; 25% DM of starch) or HS ( n = 15; 32% DM of starch) diet during the last month of gestation. Blood samples were collected on wk −4, −3, −2 and −1 relative to expected parturition, immediately at parturition (d0) and on d 1, 2, 3, 5, 10, 15, 30 postpartum in dams and goat kids. Colostrum and milk yield were recorded, and gross chemical composition, somatic cell count (SCC), Brix degrees and immunoglobulin G (IgG) concentration were determined on d 0, 1, 2, 3, 5, 10, 15, 30 postpartum. In addition, dam and goat kid blood serum metabolites and plasma IgG concentrations were determined. Data was analysed using linear mixed models in SAS (SAS 9.4) including the prepartum diet, time ( T ), and the interaction between both as fixed effects. The statistical significance was set as p ≤ 0.05. The high‐starch diet did not have any effect either on colostrum nor on milk yield, gross chemical composition, SCC and Brix degrees. However, the excess of starch on the prepartum diet increased colostrum IgG concentration on d 0 (i.e. first milking) in the HS group compared to the control group (i.e. 85.4 and 61.2 mg/mL, respectively). Serum BHB concentration in the HS group increased progressively from wk −3 to parturition (i.e. 0.20 and 0.24 mmol/L, respectively), whereas the control group showed a sharp increase from wk −1 to parturition (i.e. 0.22 and 0.29 mmol/L, respectively). Calcium, total protein, lactate dehydrogenase, urea and albumin concentrations were lower in the HS group compared to the control group during the prepartum period. The high‐starch diet prepartum did not influence serum metabolites in the postpartum period except for lactate dehydrogenase, being lower in the first 5 days after parturition in the HS group. In the goat kids, body weight (BW), milk intake and plasma IgG concentrations were not affected by the high‐starch diet offered to the dams prepartum except for an increased serum total protein concentration observed on d 1 in the HS group compared to the CON group (i.e. 7.1 vs. 6.5 g/dL, respectively). The present results indicate that a high‐starch diet during the last month of gestation does not affect either colostrum yield or composition but increases colostrum IgG concentration, although it did not affect circulating IgG concentrations in goat kids from both groups. Based on the slower fat mobilisation in the HS group, high‐starch diets prepartum could promote a smoother transition from late gestation to early lactation in dairy goats. However, other metabolic variables should be considered in future studies.