"This kid has survived so much," said McKay.
Brennagh had been "going great guns" since the bowel surgery, according to her mum, until about 12 weeks ago when green fluid started leaking into her feeding tube, signalling an issue with her bowel.
McKay said she was told by surgeons, after Brennagh's bowel surgery, that if she noticed this happening, she had an hour to get her to a hospital or she could die.
So, the 11-year-old was rushed to Palmerston North Hospital.
The green fluid, called aspirate, continued for weeks during which time Brennagh was fed very little so her bowel could rest.
"That is what has contributed to this rapid decline in Brennagh's weight loss," said McKay.
Convinced that the products her daughter was being tube fed were contributing to her bowel failure, for factors including their sugar content, and determined to stop her from becoming more malnourished, McKay started thinking about what else she could feed Brennagh to keep her alive.
"After brainstorming with a mother who has just had a baby, she said 'what if you gave her breast milk'," McKay said.
McKay decided to give breast milk a go just over two weeks ago, after doing some research. She has been adding a product called Juice Plus to the milk - a dietary supplement that contains concentrated fruit and vegetable juice extracts with added vitamins and nutrients.
"And that's all we use," she said.
"I cut everything. I cut all her drugs. I thought were going back to basics like a newborn baby because she wasn't even tolerating food that a two-year-old could eat, she wasn't even getting that much nutritional value."
McKay said since Brennagh has been having breast milk, her bowel has been functioning and the green liquid has stopped coming up her feeding tube.
"Her whole system is working like a new born baby."
At least 10 women have donated breast milk for Brennagh, however McKay said it was proving difficult to keep a consistent supply.
The mum has put out a call for breast milk on Facebook and said she has asked friends to spread the word. A Givealittle page has also been set up to help keep the milk flowing.
McKay has been picking the milk up herself or having it couriered to her home in Rongotea, near Palmerston North.
Healthy Food Guide nutritionist Claire Turnbull said a huge amount of research goes into the types of feeds used when individuals need to be tube fed. This included looking at all the requirements for energy, carbohydrate, protein and fat as well as vitamins and minerals.
"The limitation with breast milk is that [it] is a primary source of nutrition for a child up to around six months. Beyond six months babies need additional nutrients which is why we need to start introducing supplementary food.
"There are some huge advantages of breast feeding and lots of fantastic things about breast milk but still, beyond that six month mark it's not enough for even a baby."
Turnbull said the other issue with breast milk was that its nutritional value can vary from mother to mother depending on the needs of their baby. This means that sourcing breast milk from a range of mothers could make it hard to get a milk that's nutritionally consistent.
"There is a reason why specially formulated tube feeds exist. However I really do understand when people get desperate they will do anything. I completely get that."
