It is possible for an urban farmer to keep livestock. For example, a wooden structure of 10x10ft can keep as many as 20 chicken.
These give not only eggs, but also meat whenever required. They also provide organic fertilisers for vegetables and other crops.
Note that when you keep chicken or any other livestock, their droppings help with the fertilisers needed to provide nutrients to the soils before and after planting.
The chicken can easily be fed on processed feeds. You can keep rabbits too, these require even much less space than chicken.
For those with larger space of about 20x20ft, it is possible to keep a zero-grazing cow for milk. The cow, if well fed can produce at least 15 litres of milk per day.
From these, you can consume 2-3, then sell off the rest. There are now farmers who specifically grow pastures for sale to urban farmers who may not have space to grow their own pastures.
A cow needs at least feeds worthy sh4,000 per day. Use odour neutralisers that are now many on the market to keep off smell.