Quality of life of farm animals

I need your help! I'm trying to model farm animal welfare but I don't have good estimates of average quality of life among the animals.

Tomasik has his suffering calculation, but he is only looking at the quantity of suffering. That means it's only accurate if you are a negative utilitarian; I'm not one and most people here aren't either.

There are the welfare estimates in Compassion, by the Pound. However, there is a problem with them too. They go from -10 (worst farm conditions) to +10 (all animal needs are met). Even from a conventional utilitarian perspective (ignoring all possibilities for "negative leaning" utilitarianism) this is not appropriate because we generally rate suffering scales as extending farther than happiness scales. We wouldn't accept ten days in very bad farm conditions just to live another eleven days in very good ones.

And because of variance in welfare across members of an animal type as well as variance across an animal's lifetime, which are hidden behind the author's point estimates, it's not possible to straightforwardly translate these estimates into new estimates of average animal welfare which take the above consideration into account.

So, I pose the question to those of you who know about animal psychology and conditions on farms. Let -10 be the quality of life in a truly bad factory farm - not the worst possible suffering, not deliberate torture, just the worst that you would expect to find for any animal type on any farm in the world today. Now let 0 be the point at which the animal's welfare is neutral, i.e. we ought to be fundamentally indifferent between it existing or not. +10 will be the point at which animals have enough well-being to actually outweigh -10 in moral terms. So if half of animals are at -5 and the other half are at +5, the average for that species will be 0.

On this scale, how would you rate the average QOL of beef cattle, dairy cattle, pigs, meat chickens, egg chickens, turkeys, and farmed fish?