Effect of a peri-parturient eprinomectin treatment of dairy cows on milk production

AIM: To quantify and economically evaluate the effect on milk production of peri-parturient treatment of dairy cows with eprinomectin. METHODS: On 3 farms in separate geographic areas of New Zealand, 849 first- calf heifers and multiparous cows were ranked and paired within parity, dat e of calving and expected milk production. Within pairs, cows were randomly allocated to treatment with either a commercial formulation of eprinomecti n, applied at a dose rate of 500 mug/kg liveweight, or an equivalent volume of vehicle containing no antiparasitic agent and administered at the same dose volume, generally within the first week post-caving. On each farm, tri al cows shared the same pasture. Over a single lactation, records were main tained of milk quantity and content. RESULTS: Trichostrongylid eggs were identified in pre-treatment faecal samp les from all farms, verifying the presence of gastrointestinal parasites. O verall 25.5% of the cows sampled were positive for nematode eggs, but only 8% had counts greater than or equal to 50 eggs per gram of faeces (epg). Da ily milk volume, milk protein and milksolids (yield of milk fat + milk prot ein) were higher for eprinomectin-treated multiparous cows than for control s (milk volume: 20.36 l/day vs 19.76 l/day, p=0.005; milk protein: 0.700 kg /day vs 0.685 kg/day, p=0.012; milksolids: 1.613 kg/day vs 1.583 kg/day, p= 0.031, respectively). The daily value of the increased production from epri nomectin-treated multiparous cows was estimated to be NZ$0.034 for milk fat (p=0.095) and NZ$0.078 for milk protein (p=0.012), equating to NZ$0.104 fo r milksolids (p=0.031), averaged over the whole lactation. No significant d ifference in milk production was detected between treated and control first -calf heifers. Averaged over the whole herd, the peri-parturient treatment of multiparous cows and first-calf heifers with eprinomectin increased dail y milk volume and milk protein production of treated vs control cows (19.28 l/day vs 18.86 l/day, p=0.020, and 0.661 kg/day vs 0.650 kg/day, p=0.047, respectively). CONCLUSION: These data provide evidence that the use of a peri-parturient t reatment of eprinomectin on multiparous cows can increase their production of fluid milk and millcsolids.