I'm not sure if there is such a specific fanfiction. Fanfiction can cover a wide range of themes and descriptions, but this kind of rather odd and inappropriate description might not be common in mainstream Naruto fanfiction.
One common theme is alternative universe stories. For example, what if Naruto was raised in a different village? Another is exploring his relationship with his parents in more depth. Also, there are fanfictions that focus on his training and how he masters new jutsus in unique ways.
The idea of a female anthro horse and 'lemon' in Naruto fanfiction can be quite complex. If we think about it, the female anthro horse could be from a different dimension or tribe within the Naruto world. The 'lemon' aspect could be her having a very passionate and unique personality. She could be attracted to a ninja who is different from her kind. Their relationship could develop in a way that shows how love can cross boundaries, whether they be species - related or cultural within the Naruto universe. But again, it should be presented in a tasteful and appropriate way.
In a fanfiction about Hagrid, the phrase could be used to describe his loyalty. Just as a horse is known for its loyalty, Hagrid could be said to be 'hung like a horse' in terms of his unwavering loyalty to Dumbledore or his love for the magical creatures he cares for. This gives a positive and family - appropriate spin to the phrase.
There could be some Naruto fanfictions that might use the word 'hung' in a non - literal sense, perhaps referring to a character's determination or eagerness. But if it's a very specific and unusual combination, it might be difficult to find. You could try looking through Naruto fanfiction communities and asking for recommendations related to this specific concept.
Since 'hung lemon' is not a very clear or common concept in Naruto fanfictions, it's hard to recommend a specific one. But there are tons of Naruto fanfictions that are suitable for all ages. For example, those that focus on Naruto's training journey or his friendship with Sasuke are family - friendly and very engaging.
One possible story could be that the alpha, perhaps a strong - willed character, meets a horse and through some shared experiences, like helping each other during a storm, they become friends. Then their human friend comes into the picture and they all form a special bond. They might compete in friendly races or just enjoy long rides through the countryside.
The horse could be a wild mustang that an alpha - type person (someone with a strong personality) tries to tame. Their friend might be a local rancher who gives advice on how to approach the horse gently. And 'Hung' could be the name of a place where they keep the horse once it's tamed, like a ranch called Hung Ranch.
A common plotline in such fanfiction is the exploration of their relationship further. Since Kushina died when Naruto was young, fanfictions often show them getting to know each other better. It could be something like Naruto learning more about his mother's life before he was born, like her training as a ninja, her friends, and her dreams. And Kushina could get to know Naruto's friends and see how he has created a new family of sorts in the form of Team 7 and the rest of the village.
Well, while 'lemon' often implies mature or inappropriate content in fanfiction, if we consider more family - friendly interpretations, there could be some creative stories. For example, a story where a female horse in the Naruto - inspired world has some sort of unique bond or adventure with the Naruto characters. But truly, finding such a story that is both in line with the odd combination and suitable for all is quite rare.