Your writing here is perfectly coherent with good grammar and punctuation.
If this is your normal writing style then I think you're much too hard on yourself.
If you've dictated this to a computer to type, you're still very capable in language terms.
If you're on PIP, do you also claim ESA, Housing Benefit and Council Tax Credit etc or UC?
Do you drive? If so, your skills in observation, decision making and being able to take the pressures of driving will be higher than you think they stress.
PDA is probably the biggest boundary here from what you've described.
Qualifications are not the be all and end all, but to work for someone you'll need to be able to take instruction, carry out allotted tasks, understand and abide by rules such as health and safety, timekeeping etc - is that achievable?
Working with animals and especially in agriculture is a type of work that's been highly professionalised over the years, hence the qualifications required.
Could you visit or contact an agricultural college to discuss your options?
Have you been able to do things like volunteer roles in the past?