I’m guessing this is a techie reference.
Computer servers can be divided into two roles in modern technical architectures… they are either “cattle” or “pets”. Pets are computer servers that have names and are always up. Cattle are servers that are transient, spun up and down as needed and do not necessarily have any long running identity/name as a component of a larger system.
http://cloudscaling.com/blog/cloud-computing/the-history-of-...
The poster is making a critiques of how by treating historical persons contributors as cattle, we are considering them a dispensable, unnamed, a commodity that is easily replaced and interchangeable and missing their very real contribution, value, and humanity.