Effect of a Sustained-release Bolus on Milk Production, Rumination and Reproduction in Multiparous Dairy Cows Classified at Low Milk Fever Risk

The aim of this study was to determine whether the positive transition health, rumination, production, and reproductive responses to Cow Start Complete (CSC) supplementation seen in high milk fever risk Irish and UK studies, extend to multiparous dairy cows managed under low milk fever risk conditions in a NZ pasture-based system using once-a-day (OAD) milking during early lactation. Seventy-one multiparous crossbred dairy cows (3rd – 5th Lactation; 29 CSC-treated, 42 controls) received either 2 x CSC sustained-release boluses at calving or no supplementation. Outcomes observed included transition health performance, rumination behaviour, milk volume and milk solids production (weeks 4–24), and reproductive performance. During the first week after calving, daily rumination levels dropped more in the control group than the treatment group (control – 33 mins/day, p = 0.009 vs treatment – 1 min/day, p = 0.947). In terms of milk production, across weeks 4-24 in lactation, the CSC-treated cows produced 1.3 L more milk per day (+4.5%, p = 0.039) and 0.11 kg more milk solids per day (+3.86%, p = 0.037). Reproductive performance improved in CSC-treated cows when compared to the control cows, higher first-service conception rate (89.7% vs 63.1%, p = 0.015), fewer services per conception (1.1 vs 1.5, p = 0.012) and 9 fewer days to conception (p = 0.034). In a pasture-based herd managed under early lactation OAD milking, CSC supplementation at calving was associated with improved milk volume and milk solids production, reduced early-lactation rumination suppression, and improved reproductive performance. These findings indicate that the CSC sustained-release bolus may confer benefits beyond traditional high-risk hypocalcaemia populations.