After over 5 months of development I am excited to finally share with you the beta version of Truth and Beauty: Detailed Animals! Currently we have a nutrition system, a genetics system, and a number of tweaks.

Nutrition: Keeps track of how much the animals have eaten, how much they weigh, and how healthy their diet is based on whether they've eaten the right amounts of fiber, protein, etc for their species. Improves accuracy on which foods each species can eat. Allows hand-feeding foods to animals or feeding them from the existing troughs. They can also get food from grazing or rooting around in the soil. Very young mammals can have milk from their mothers. Growth to adulthood is gradual and comes with increased nutritional needs especially for protein.

Genetics: Most of the work here has been on back-end support for being able to have genetics at all. On the frontend, you'll see new and more detailed chicken textures in 10 different plumage colors, which follow realistic genetic inheritance. Genetics and breeding are meant to be less of a focus than care and husbandry.

Real quick, here are the main practical impacts on gameplay, though not what the mod is really "about":

 - Butchering drops from all animals have been adjusted to be consistent based on real-life relative sizes. No more getting paltry scraps from a moose.

 - Animal breeding now takes place in accordance with the seasons, making it generally much slower. Animals are able to breed in the wild, but it will likewise be very slow.

 - Cassava can be grown safely outside a fence, as like onions it is poisonous to all in-game animals and they won't eat it

 - I taught the bears how to steal berries off your bushes and honey from your skeps, like the raccoons. You're welcome :)

Nutrition

Animals need to eat food regularly. Most species will be able to take care of this themselves if given an appropriate space to forage. Herbivores can graze, and pigs can root around in the dirt for, well, roots. Very young mammals nurse from their mother, or rarely from a foster mother of the same species. Over time they'll gradually start eating solid food more often until they are fully weaned. You can also hand-feed an animal by right clicking with an appropriate food, or leave it in a trough or dropped on the ground for them to munch on.

Here are the hunger levels you may see:
Starving - In a bad situation and losing weight fast
Famished - Desperate for food
Very hungry - Has been hungry for a while and is beginning to feel worried
Hungry - Would like to eat food now
Somewhat hungry - Might maybe like to eat food, or maybe wait until later
Peckish - Might accept some food if offered, but more focused on other things
Not hungry - Has eaten enough food for now, but may still get tempted if offered something extra tasty
Full - Has eaten enough food and more would be unhealthy
Stuffed - Cannot possibly eat another bite no matter how tasty

Note that hunger has no effect on anything except food pickiness and weight gain or loss. Weight as part of body condition is what actually matters.

Different species have different nutritional needs, for instance goats need more fiber in their diet than pigs do. Certain species are able to eat items not normally considered food, for instance grown wolves can crunch bones. Foods that closely match the animal's nutritional needs will give small bonuses. Animals may refuse to eat a food if the nutrition it provides is very different from what they currently need. For example, pigs can eat a little bit of grass, but would like a more nutritious food for the main part of their diet. Sheep on the other hand will be healthiest eating mainly grass or hay. Animals will also refuse very sour foods such as lemons or pickles.

Creature weight no longer changes semirandomly with the seasons. Instead, animals who don't eat enough will lose weight, while those that eat too much can gain weight. You can see an animal's weight in pounds and/or kilograms depending on the config. I have endeavoured to make the weights shown as accurate as possible for the animal's species, sex, age, and condition. (No thanks to all those websites playing telephone and turning "can grow up to a maximum of X pounds in rare circumstances" into "weighs X pounds on average".) Females will generally weigh less and also look smaller than males depending on how much sexual dimorphism is typical for the species.

Here are the body condition levels you may see (actual effects on health and stats still WIP, but until then picture them as this):
Skin and bones - Extremely low weight, in bad shape and very unhealthy
Malnourished - Unhealthily thin, needs to eat more
Underweight - Should regain weight to be healthier
Lean - Healthy with little to no spare fat
Moderate - Healthy, medium
Thick - Healthy and on the heavier side
Chubby - Starting to get just a little bit too fat
Fat - Gained an unhealthy amount of weight
Obese - Way too fat, in bad shape and very unhealthy

Weight affects what you can get from butchering an animal. Meat is roughly proportional to total weight. Fat is strongly affected by condition, with very underweight animals dropping none at all and plump animals dropping lots extra. To discourage players from mistreatment, no bonus is given for animals at an unhealthy level of obesity. Hides are roughly proportional to surface area, that is, weight to the power of 2/3.

Newborn animals will gain in size and weight gradually as they grow up, which comes with an increased need for protein in the diet. Young animals will not need to eat as much as adults, because they are smaller, but they will need to eat more relative to their weight than adults, because they are growing. Most species begin to look and act as an adult quite some time before they reach their full size. They will continue to gain weight during this time, but generally at a much slower pace than when they were young.

Pressed fruit mash now takes longer to spoil (5 days instead of 1.5), making it a more viable animal feed.

As a related tweak, hares no longer eat out of large troughs.

Genetics

Chickens have been given three color genes: extension (duckwing, birchen, extended black), blue/black/splash, and recessive white. Together there are 10 different possible plumage colors. Even with a rooster around, there's no guarantee that every egg will be fertile. The chance of eggs being infertile will increase if the chickens are inbred, but can be decreased.

Included in this mod is a library (Genelib) allowing other modders to add genetics to animals with a relatively small amount of code. If you're very adventurous you can do that already, but beware that the API isn't considered stable until we have a 1.0 release.

Along with genetics are some changes to breeding. Pregnancy and egg incubation lengths are now accurate and consistent with the length of an in-game year. The animals will go in and out of heat on their own, you don't need to worry about this but can just see what's going on as either "Ready to mate" or "X days until ready to mate". Most species breed seasonally - goats, deer, sheep, pigs, gazelles, and wolves during the fall and winter, hares, foxes, chickens, and raccoons during the spring and summer - but hyenas can breed at any time of year. You may notice that many of these species were not able to breed before, but now they can. Once the offspring are born, you'll be able to see which gender they are right away without waiting for them to grow up. 

Animals are able to breed without player interaction as long as they were able to forage for enough food to stay in healthy condition. However, generation will not increase unless the mother has been fed by the player at least once in her life. Hand-feeding and feeding from troughs both count.

Nestboxes have been modified to allow genetic data to pass to the next generation. While I was at it, I fit in an extra egg (so they hold four, not three) and also made it so you can take eggs out and put them back without them instantly losing their fertility. New egg items have been added that look more egg-like. They come in different sizes, however chickens have not yet been given the ability to lay different sizes of egg, so you'll only be seeing medium eggs. To help the chickens know what the nestbox is for, you can make fake eggs out of clay and leave them inside. For technical reasons, the ability for chickens to lay an egg on the ground has been temporarily removed, but will hopefully come back in a future version.

Tweaks

 - Female goat-antelopes have horns, and female caribou have antlers.

 - The timing of antler growth and shedding has been adjusted to be a bit more accurate.

 - Gazelle calves have a more accurate hitbox size, and are capable of growing into adults eventually.

 - You can craft a creep gate, which allows small animals to pass underneath while still blocking larger animals.

 - Baby hares are called "leverets".

On existing worlds

Yes, you can use this on existing worlds. There's just a couple things to be aware of:

 - For the chicken genetics to work, you'll need to change out any henboxes you already have for nestboxes, crafted using the same recipe. (On version 0.1.5 and later, you can simply pick up your existing henboxes and put them down again, they'll transition when they go from being a block in the world to being an item in your inventory.)

 - The feature where baby animals have genders won't kick in right away. It'll only be for new animals born after the mod is installed.

Other than that, you should be able to add this to existing worlds with no issues.

With other mods

Especially recomended:

 - Berry Bush Fixes: Fixes the vanilla bug where berry bushes take forever to ripen after being harvested by an animal.

 - Fruitpress Fixes: Makes the fruit mash stack properly, making it easier to feed to your animals.

 - Animal Cages: Note you will need to adjust the config like so to catch gendered baby animals:

Depends on playstyle:

 - Grassier Grass: Makes hay collection easier and fairer by letting you scythe more from taller grass.

 - Natural Trails: Makes you need much larger, more realistic pasture sizes as sheep and other grazers may trample some of their grass (details configurable).

 - Every mod not specifically mentioned goes here, I guess

Minor incompatibilities but overall still recommended:

 - Wolf Taming: Wolf pups can become a different gender of wolfhound, so if you're taming one just pretend it's still genderless

 - Cuniculture: Lets you put more types of food into small troughs, but hares will have a purely visual effect where breeding info is shown twice.

 - Expanded Foods: Eggs cannot be cracked, but can still be hardboiled, pickled, water glassed, used in pies, or used (whole) in scrambled eggs.

Major incompatibilities:

 - Animation Manager Lib: Causes off-by-one errors on every clientside behavior patch

 - Creatures and Critters (unofficial): Patch conflicts for multiple species may cause animals to act strangely

 - Butchering: Game crashes if you attempt to butcher certain textures of chicken, but keep an eye out for newer versions of Butchering which may fix this

Languages

Supports English, Spanish (Español), German (Deutsch), Polish (Polski), and Russian (Русский).

Thank you to Niexyk, BradyThe, and ИгОорКа for providing translations.

You're welcome to join the discord and ask questions or share your animal adventures. It's shared with my mods for that other block game.

Development

If you find a bug, please let me know on discord or on the github issue tracker.

Does not yet work on 1.20, but an update is in progress.