A treaty is an instrument of hard law. At the universal level, it would be legally-binding for all states. A universal treaty on animal rights can lead, in an ideal future, to respect the basic rights of animals (life, integrity and freedom), those rights recognized in the the Universal Declaration of Animal Rights
(UDAR), political rights and others.
Such an instrument can also lead to general bans on animal (ab)uses which go against the proclaimed rights of animals, or against any practice generating avoidable suffering or disrespect to animals. This treaty can even create general obligations for humans to assist animals in distress, to respect them and to represent their interests in any legal, social and political fields. It can also require to take into account animal interests in every sphere of life, science, politics, production and consumption, leisure, media et cetera.
This, for the moment, "utopian" treaty, can be based on the general principle that animal rights and human rights are equals, considering that both humans and other animals are members of the animal community. In this sense, any human right (e.g.: economical, scientific, educational, recreational, artistic, cultural, ritual etc.) would not trump a corresponding non-human animal right (as held by equally important individuals even if connected to different species).Thus, the abolitionist and egalitarian theory of animal ethics would be translated into a binding instrument at universal level. The universal status of animals would then be the legal personhood, as opposed to things or property. Therefore, it will no longer be possible to use animals for any kind of human purposes (production, experiment, entertainment, etc.), as far as such uses - and the suffering or poor welfare derived from them - can be avoided.
As for the limits of such a recognition, what now applies in the human case, would equally apply for non-human animals (on a case-by-case basis). For instance, in case of imminent danger for one's integrity or life, the principle of self-defense would equally apply. The answer would have to be proportional to the threat, considering all the available options to avoid any prejudice to the other's integrity or life. As a basic law of nature driving every form of life on earth, the self-preservation principle would be recognized for every individual and species. Once legally recognized in a universal instrument, the common ethical principle of respect for life (present in every culture and religion since ages), can also lead to more consideration for every animal and condemn any cruel acts, ill and disrespectful treatments - or any damage to an animal’s life and integrity (either psychological or physical) anytime the self-preservation principle is not at stake.
Such an instrument can also lead to condemn all crimes against animality (adapted from the crimes against humanity), such as: torture, species extinction (genocide), zoophilia (rape), captivity (sequestration), exploitation (slavery) etc. They can be addressed either by the International Court of Justice (ICJ) or by a special universal Court (to be created), able to judge private and public persons (individuals, states, corporations, national and multinational firms or labs etc), accountable for their crimes against animality.