As for regulations that apply to the the welfare of cattle being shipped via the high seas, oversight is very, very dim - at best.
The 28-hour rule goes out the window once a vessel enters international waters, says Joelle Hayden, public affairs specialist at APHIS. Hayden said she was unable to answer questions about how long each overseas journey takes, because shipments in international waters aren't in the USDA's jurisdiction: "USDA regulations require animals are provided with food, water and sufficient space during their journey. That is the extent of our authority," she notes.
There's no official count, or even estimate, of how many cattle die per year or per shipment, explains Hayden. However, she does note that the USDA recently proposed a rule that would require owners of ocean vessels to submit a report within five business days of completing a voyage as an effort to document livestock deaths, including "any failures of life support systems," like air conditioning, she added.
The World Animal Protection campaigns against live export and especially condemns transport by sea: "The trauma that ... cattle endure during their voyage overseas makes live animal export truly unacceptable ... The conditions on board ship are so harsh that the animals suffer severe distress, illness and injury, and many die before they reach port."