Non-inferiority, randomised clinical intervention study comparing the effect of two injectable trace element products on reproductive outcomes of adult pasture-grazed dairy cattle

AIMS: To determine if a novel injectable product containing zinc, copper, manganese, selenium and cyanacobalamin (ZMSC) was non-inferior to a reference product containing zinc, copper, manganese and selenium (VMM) for: 6-week in-calf rate, final pregnancy risk, conception risk to first service, and 3-week submission rate (all at a 5% non-inferiority margin). METHODS: , copper, manganese, or zinc concentrations outside laboratory reference ranges. Reproductive data from farm records were analysed from cattle treated with either ZMSC (n = 1,903) or VMM (n = 1,898) approximately 4 weeks before the start of mating. Statistical analysis incorporated mixed-effects logistic regression models, adjusted for farm, age, and treatment for non-visible oestrus. Non-inferiority was assessed using estimated marginal means, converted to proportions. Superiority was assessed when non-inferiority was established. Time to conception was evaluated using Kaplan-Meier survival curves and Cox proportional hazards models in a two-sided hypothesis-testing framework. RESULTS: ZMSC demonstrated non-inferiority to VMM across all reproductive parameters: no meaningful differences were observed between treatments for 6-week in-calf rate (OR = 1.12 (95% CI = 0.96-1.31), p = 0.14), final pregnancy risk (OR = 1.06 (95% CI = 0.86-1.30), p = 0.6), conception risk to first service (OR = 1.06 (95% CI = 0.93-1.21), p = 0.4), and 3-week submission rate (OR = 1.18 (95% CI = 0.90-1.54), p = 0.2). Time to conception was also similar between groups (HR = 1.04 (95% CI = 0.96-1.13), p = 0.36). Although non-inferiority was established for all outcomes, the data were consistent with the conclusion that ZMSC was not superior to VMM. CONCLUSION: The ZMSC product was non-inferior to VMM across multiple reproductive measures in pasture-grazed dairy herds with good baseline reproductive performance and no evidence of trace element deficiency. This supports ZMSC as a comparable alternative to VMM in herds with similar characteristics. Interpretation should remain within the study scope, which assessed comparative performance between active treatments rather than absolute efficacy relative to no injectable trace element supplementation. CLINICAL RELEVANCE: Supplementation of cows with ZMSC as an alternative to VMM is likely to produce comparable reproductive performance in dairy herds.