Accuracy and precision of diets fed to close-up cows on dairy farms and its association with early lactation performance

Ensuring a consistent ration is critical for maximizing lactating cow performance, but this is not known for dry cows. The objectives of this cohort observational study were to: (1) characterize close-up dry cow diets fed on commercial farms in Ontario, Canada, (2) describe the accuracy of the nutrient composition between the formulated close-up diet and the diet offered to the cows, (3) describe the precision of the close-up diets across time, and (4) explore potential associations of that accuracy and precision with blood metabolic parameters and milk yield of cows in early lactation. Forty freestall dairy farms were visited once every 4 wk, for a total of 6 visits to each farm, from April to October 2022. At each visit, samples of the close-up diet were collected and analyzed for DM content and chemical composition. Close-up diet formulations were also obtained by each farm's nutritionists. During each visit, fresh cows (0 to 14 DIM) had blood samples taken for blood metabolites. The same cows were also monitored for milk yield up to 120 DIM. Multivariable models were used to analyze associations between variability (in relation to the formulated diet and across time) of nutrients in the close-up diet, as measured by CV, and outcomes in fresh cows. Corn silage (67.6% of farms) and straw (24.3% of farms) were the predominant primary forage sources used in the close-up dry cow diets. Soybean meal (37.8% of farms) and canola meal (18.9% of farms) were the main ingredients used as primary concentrate sources. Overall, the diets offered did not accurately represent the formulated diets. With the exception of NE_L, the CV for the other nutrients were all greater than 5%. Diet variability, both between fed and formulated diets and from visit to visit during the close-up period, was associated with metabolic markers and dairy cow production. Lower variability in NFC between the fed and formulated diets was associated with better liver health index scores. Visit-to-visit variability in fat percent and NFC percent were associated with blood BHB concentrations, and NFC percent variability was associated with blood glucose levels. Serum nonesterified fatty acids concentrations were associated with visit-to-visit variability in DM percent and CP percent. These results underscore the importance of maintaining consistency between diet formulations and feeding practices over time to optimize early lactation dairy herd performance and health, granted that these diets are correctly formulated to meet the nutritional needs of cows in the close-up period and applied with recommended feeding practices.