Drop-ship orchestration, how do you wire Henry Schein AH, Patterson Vet, MWI, Covetrus?

Magento as the order-of-record, distributors as fulfillment back-ends. Each of the four big distributors has a different integration surface:

• Henry Schein Animal Health, EDI 850/855/856/810 over AS2 or VAN. Mature, well-documented, but EDI is EDI, expect a 4-6 week onboarding with their integration partner. SKU master pushed via flat file weekly.
• Patterson Veterinary, similar EDI flow, also has a REST partner API for smaller resellers. Ask for the “Patterson Web Services” doc, not on their public site.
• MWI Veterinary Supply (AmerisourceBergen), the largest by volume. EDI 850/855/856/810 + a real-time inventory check API. Tightest integration of the four if you’re a high-volume reseller.
• Covetrus, REST API + EDI options. Best documentation, fastest onboarding for new partners. Sometimes the place to start.

Auto-PO routing logic in Magento: for each line item, check stock across all wired distributors, pick the cheapest in-stock for the ship-to ZIP, generate PO, send via EDI/API, ingest 855 (acknowledgement), 856 (shipping notice), 810 (invoice). ETA surfaced on order confirmation. Tracking pushed back to customer email. Avoids the “phone four distributors to find Bravecto” chaos most independent vet-supply resellers live in.