ankle_cuffs balls barn blue_hair blue_mane blue_tail bodily_fluids bound bridle chastity_cage chastity_device chest_tuft cloud cuff_(restraint) cuff_bracelet detailed_background dripping ears_up farm feral fetlocks field flower fur genital_fluids genitals grass hair harness hooves indigo_furry_mix_v120_hybrid indigofurrymix_(model) leaking_precum legs_tied light light_hooves looking_at_viewer male mane metal_chastity_cage multicolored_hair multicolored_mane outdoors outside petplay plant ponyplay precum precum_drip precum_string prompt red_eyes red_hair red_mane red_tail restraints roleplay rural saddle sky solo solo_focus standing straps submissive submissive_feral sunlight sweat sweaty tree tuft two_tone_hair two_tone_mane two_tone_tail white_body white_fetlocks white_fur mechanic_31 my_little_pony earth_pony equid equine horse mammal pony 1:1 colorful detailed full-length_portrait hi_res portrait prompt_metainfo shaded story story_in_description
Here is another stallion from the farm, but his job is somewhat different from the rest of the ponies. While most of the ponies whose home the stable has become are used in small-scale trucking to pull carts, this stallion is mainly used for education purposes. 
At the moment you can see him under the saddle - this means that someone is waiting for basic horseback riding training. Unfortunately, equestrian ponies are too small to support the weight of an adult man, so they are mainly used to train riders with low weight. So, most of the students are high school students and students junior courses. This kind of training is especially interesting for girls aged 16-21, having learned to confidently ride ponies in the saddle, some then sit on ordinary, large horses. 
However, horse riding is not the only part of training, girls are also taught how to handle ponies, take care of them - so that the students can then work independently with ponies on farms and in other places. In addition, girls are willing to learn how to work with ponies also because the acquired skills of control and domination can be used not only in relation to ponies - such mistresses are very popular with submissive guys.
Speaking of what we see in the image, the pony was saddled by the master, and most likely, the first student trained on it for some time, which is why the stallion managed to get excited and sweat. After this training, the pony's movement was limited, and now he has a short break before the next student and a new training session, which the stallion has to wait with his legs tied. It is quite possible that this restriction is imposed on the pony as a punishment for some actions. When the student arrives, they will most likely have advanced trotting training, and most likely the stirrups were removed from the saddle for this.
And of course, when it comes to education, especially for young students, safety comes first, so various restrictions, and especially chastity, are mandatory for ponies. [i]Only the most experienced students can fix the pony in the stall after training, and remove the cage from it, rewarding for good behavior and obedience with an extraordinary milking.[/i]

[i](Due to the strong excitement of the stallion, during the training (up to the release of precum), the question of having any objects under the stallion's tail is given to your imagination.)[/i]

(Yes, there is a funny mistake in the negative, I noticed it already before publication. the picture is really generated with such a prompt)

[b]Prompt: [/b] MLP pony in harness work on farm, feral pony, harness, bridle, field, sweat, slavery, by swaybat, bit gag, hooves, my little pony, standing, (balls, chastity), chastity cage, dripping precum, male, cuffs, saddle 
[b]Negative:[/b] /setnegative boring_e621_fluffyrock_v4, deformityv6, easynegative, bad-hands-5, bad anatomy, low quality, signature, logo, watermark, narrow eyes, empty eyes, blind, white eyes 
[b]Size:[/b] 768x768 Sampler Steps: 20 CFG Scale: 9.00 Model: indigoFurryMix_v120Hybrid Seed: 1356915897 
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[b]Upscale:[/b]
Size: 1536x1536 Sampler Steps: 15 CFG Scale: 9.00 Denoising Strength: 0.45 Seed: -348229336