Here is one take on the matter, from Mike Archer, controversial to be sure, and in some ways under-argued, but offering some points to ponder:
… the largest and best-researched loss of sentient life is the poisoning of mice during plagues.
Each area of grain production in Australia has a mouse plague on average every four years, with 500-1000 mice per hectare. Poisoning kills at least 80% of the mice.
At least 100 mice are killed per hectare per year (500/4 × 0.8) to grow grain. Average yields are about 1.4 tonnes of wheat/hectare; 13% of the wheat is useable protein. Therefore, at least 55 sentient animals die to produce 100kg of useable plant protein: 25 times more than for the same amount of rangelands beef.
You will note that this comparison works for grass-fed beef only.
Hat tip goes to Dalibor Rohac.