[L]ike nonhuman animals in human factory farms, free-living nonhumans who are starving - or being disembowelled, asphyxiated or eaten alive - cannot … - David Pearce

All moral tradeoffs are messy. However, on some fairly modest ethical assumptions, when a severe and irreconcilable conflict of interests occurs, then the interests of the more sentient take precedence over the less sentient. This rule of thumb holds regardless of the age, race or species of the victim.

The Hedonistic Imperative outlines how genetic engineering and nanotechnology will abolish suffering in all sentient life.
This project is ambitious but technically feasible. It is also instrumentally rational and ethically mandatory. The metabolic pathways of pain and malaise evolved only because they once served the fitness of our genes. They will be replaced by a different sort of neural architecture. States of sublime well-being are destined to become the genetically pre-programmed norm of mental health. The world's last aversive experience will be a precisely dateable event.
Two hundred years ago, powerful synthetic pain-killers and surgical anesthetics were unknown. The notion that physical pain could be banished from most people's lives would have seemed absurd. Today most of us in the technically advanced nations take its routine absence for granted. The prospect that what we describe as psychological pain, too, could ever be banished is equally counter-intuitive. The feasibility of its abolition turns its deliberate retention into an issue of social policy and ethical choice.

The irrationality of the "appeal to Nature" is illustrated by a simple thought-experiment. Imagine, fancifully, if starvation, disease, parasitism, disembowelling, asphyxiation and being eaten alive were not endemic to the living world - or such miseries have already been abolished and replaced by an earthly paradise. Would anyone propose there is ethical case for (re)introducing them? Even proposing such a thought-experiment can sound faintly ridiculous.