Note: When we discuss an organism's "moral weight," ultimately what we mean is whether or not its existence should be prioritized over others' in the event that a choice between one or the other had to be made. "Moral weight," "moral value," and "value," and "worthy of existential priority" are all essentially synonymous.
Which is more likely to contribute a useful idea in preventing the potential apocalyptic scenarios, such as an AI takeover or Yellowstone erupting: a human or a chicken? Obviously, a human. In addition to the plausibly increased capacity for organisms with a greater breadth and quantity of synaptic connections to experience consciousness and suffering, the moral value or "moral weight" of an organism also depends upon the organism's CREATIVITY - i.e. whether or not it can produce ideas and objects that aid in the universal fight against extinction and entropy that is an eternal existential threat against all living organisms, and the entire history of living organisms that have ever lived.
Because organisms with higher neuron counts are simply more likely to generate new and potentially extinction-preventing ideas, it makes sense that those organisms, in terms of their health and preservation, should be valued above all other organisms. Furthermore, higher-neuron organisms also have a higher potential to generate ideas that would increase the quality of life and symbiosis with lower-neuron organisms. What is the point of prioritizing (i.e., allocating resources to) a lower-neuron organism equally or more than a higher-neuron organism if doing so would only increase the probability of extinction (and decrease the probability of innovations towards symbiosis being made)?What I am not seeking to imply: This does not mean that we humans HAVE to consume all other organisms of less neural capacity, and in fact it could be argued that the quality of our synaptic connections would be better, and therefore increase the probability of producing extinction-preventing and symbiosis-innovating ideas, if we were not burdened with the guilt of abusing our fellow earthly creatures. The ethical answer to the fundamental problem that this proxy quantification is attempting to address - i.e., the morality of factory-farming: If we come to a point, for any reason manmade or natural, where there are only enough resources to sustain human beings and no other animal species on the planet, then we should allow all other species to die and humans to live; otherwise, the probability that all evolutionary history will be erased and all life on Earth will go extinct will increase because animals will not have the capacity to address other probabilistically impending extinction events with the same capacity that humans would be able to. Until we reach that point, we should strive to minimize the cruelty within the main means of food production - e.g. the self-evidently horrific practices of unanesthetized castration, forced impregnation, or debeaking in factory farming. However, we must do so while recognizing that the means of production itself is necessary to provide food affordability that wards off starvation for humans, and that such means of production does not necessarily have to coexist with the cruelty that mars it.
As we strive to outlaw the cruelty in the factory farming praxis, we should concurrently strive to build more efficient food infrastructure that can optimize food distribution to prevent food waste and make it so that the animal suffering that went into the food (which is not negligible simply because it is plausibly of a lower gradation than that of a human being's suffering) is put to the best possible use: the nourishment of a human being, the highest neuron-count organism that has ever existed on Earth. Thus, we would simultaneously achieve several benefits, well cost-effective and worthy of investment: (i) We would increase the quality of meat production
(ii) We would eliminate costs of over-production
(iii) We would eliminate emissions and land pollution caused by food waste.
(iv) Like the water cycle but with food: The infrastructure would transport food waste to massive compost centers, which would be an alternative, zero-cost fertilizer and thus lower the cost of fertilizer and therefore crops themselves ...