Question: Since we know meat is available only with killing on one’s behalf, does eating several cockles create more or less negative karma than eating a piece of beef?
Answer: Generally, the larger the sentient being is, the more developed the nervous system is, which leads to more intense experience of pain when being killed. As an example, a small cockle’s pain is less than a big cow’s pain when being killed.
In this sense, as causing (or conditioning) of pain creates negative karma, there is more negative karma created in killing a cow than a cockle – if the intentions, methods and effects of killing have no significant differences in both cases. (Killing with a more hateful intention, with a more cruel method, and for more disastrous effects, such as to inflict more mental suffering, creates worse karma.)
The above does not mean it is ‘better’ or ‘alright’ to kill cockles, as the Buddha discourages killing of all sentient beings great and small. This also does not mean that killing many cockles is definitely lesser in negative effect than killing a cow, as it is hard to quantify the complex dynamics of karma ‘mathematically’.
Some might think eating a few big animals creates less suffering than eating many small animals. However, although a cow can ‘feed’ many people with one death, there is much pain caused by that one death alone.
To conclude, the Buddha would surely rather us to avoid killing and supporting of killing, regardless of the size and number of animals involved. To heed this is to cultivate universal loving-kindness and compassion for all beings. To rationalise some killing as being more ‘justified’ goes against this practice.