Association of herd hyperketolactia prevalence with transition management practices and herd productivity on Canadian dairy farms-A retrospective cross-sectional study

The objective of this observational study was to as-sess the relationship between herd-level prevalence of hyperketolactia (HPH) with management practices of the transition period and herd milk production. Dairy herds (n = 71) were selected based on their inclusion in a herd management risk assessment study (August 2014-March 2018) using a Vital 90 (Elanco) Risk As-sessment tool (one assessment per farm). Data from multiple milk recording test-days (Dairy Herd Improve-ment, DHI; Lactanet) were included in the analysis. Tests performed within +/- 6 mo relative to each farm's risk assessment date were included (10 +/- 2 SD tests per farm). The majority of the farms were located in Ontario (83%). For each farm DHI test, the data set included herd average milk yield (kg/cow per day), average milk fat and protein (%), average somatic cell count (cells/mL), average days in milk (DIM), number of cows tested for ketosis, number of ketosis-positive tests (milk 0-hydroxybutyrate >= 0.15 mmol/L), and proportion of cows by parity groups. Overall HPH (5-21 DIM) was calculated based on data available per farm (sum of all positive tests within 5-21 DIM/ sum of all cows tested within 5-21 DIM). Each farm average was obtained by considering all test-days. A logit-transformation was applied to hyperketolactia prevalence. Linear regression models (PROC GLM and MIXED of SAS, Version 9.4) were used to predict herd HPH (milk 0-hydroxybutyrate >= 0.15 mmol/L within 5 to 21 DIM; the outcome of interest). Four initial mod-els (far-off, close-up, and fresh periods, and DHI) were separately built to assess associations between their variables and HPH; a final model considered variables selected in the initial models. Univariable (liberal P < 0.25) followed by multivariable models were used to build specific models for each period of the risk as-sessment. Herd prevalence of hyperketolactia was 27 +/- 14%, with an average herd size of 141 +/- 110 cows. The final HPH model (R2 = 24.8%) included weighted milk yield, the proportion of primiparous cows, water access in the close-up period, and access to rest areas or stall access in the fresh period. Herd prevalence of hyperke-tolactia was negatively associated with milk yield [odds ratio, OR = 0.96 (95% confidence interval 0.92-0.99)] and proportion of primiparous cows [OR = 0.98 (0.96- 0.99)]. The odds of hyperketolactia were greater with poor water access and quality (<5 cm of linear access per cow; dirty water; only 1 water location in pen) than with >= 10.2 cm of linear access per cow; clean water; >2 water locations in pen [1.23 (1.11-2.39)] in the close-up period. The odds of hyperketolactia were greater in farms providing limited access to rest areas in the fresh period than in farms providing constant access to rest areas, without dead-ends [1.64 (1.03-2.80)]. In Cana-dian dairy herds, HPH in early lactation was associated with certain transition-period management practices and was negatively associated with herd productivity.

Automated summary

This observational study aimed to assess the relationship between the prevalence of hyperketolactia (HPH) at the herd level and management practices during the transition period and herd milk production. It found that HPH in early lactation in Canadian dairy herds was associated with certain transition-period management practices and was negatively associated with herd productivity.