Helen Davies of the Rainbow Rehoming Centre says that one rescued dog had to have an eye removed because of ill-treatment, another is chronically obese and a young dog was found with a surgical pin protruding from his hip.
However she reports that more people are coming forward to rehome dogs and cats - and that the organisation's website has recorded hits from all over the world, including America.
Potential rehomers are also travelling from Belfast to offer abandoned pets a home and now the Helen says that staff are looking out for new, larger premises.
Currently at the centre is Kerry Blue Terrier 'Teddy' - who is recovering from surgery to remove his badly damaged eye.
"Teddy was found by one of our volunteers tied to a barbed wire fence between Omagh and Strabane," said Ms Davies.
"He had been treated very badly. His eye was so shrunken and badly damaged, it was hardly there so we had to have it removed. This is an injury which would have been occuring for a long time before he was picked up.
"He is only about 18 months old and he has a lovely nature, it is such a shame someone treated him like that."
Another resident is Bruno, a chocolate Labrador, who is very overweight.
"Bruno was seen being dumped out of the back of a 4x4 close to the centre," said Helen.
"He is about three years old and we are trying to get some of the weight off him."
A German Shepherd was another of the many dogs let loose close to the centre, but the organisation also now takes animals from Derry City Council's dog pound, which destroys dogs after seven days if they cannot be rehomed, sold or returned to their owners.
One of those was a young collie, which had in the past undergone extensive surgery but was found roaming with a metal pin protruding from his hip.
"That wee dog was only young and had obviously had a big, expensive operation to pin his hip, maybe he had been hit by a car or something, we just don't know.
"When he was found he was very underweight and the pin was sticking out of his body. We just can't understand why people would spend money on an expensive breed like a Kerry Blue Terrier or surgery like a pinned hip, and then either abandon them or not move heaven and earth to find them again if they were lost or stolen."
However it is not all bad news for the centre, not least because of the success of their website, www.rainbowrehoming.com.
"The website is being updated very frequently by staff member Louise Graham. We are getting hits from all over, including America, and people from Belfast have been coming to look at dogs and cats after reading about them on the internet.
"In fact lots more people are coming forward to rehome animals, and that is very good news.
"We are actually on the lookout for new premises to buy, a few acres with outbuildings, as we do need to expand our facilities."
Helen has also reminded cat owners that kitten season is imminent and has asked anyone who wants financial assistance to have their cats neutered to contact the centre on 028 7181 2882.
She added: "We are as always expecting an influx of kittens as the breeding season starts and would ask cat owners to neuter their cats to help prevent unwanted cats who all to often end up with us here at Rainbow."