Why are portholes being used on cows?
A video showing researchers using a porthole to gain access to a cow's stomach has been criticised by an animal rights group in France.
Portholes are openings on the side of a cow that allows researchers to access an animal's stomach with a cannula.
The group L214 posted a video of a researcher putting their hand into a porthole. It was allegedly recorded at Sourches Experimental Farm in northwestern France.
LS214 claims it is an "unfair system".
But experts say that in some cases cows with portholes live longer.
So what are portholes and why are people using them today?
Jamie Newbold, Academic Director at Scotland's Rural College told the BBC that studying cows' stomachs is important if "we are going to maximise food production and minimise greenhouse gases".
There are three ways of studying a cow's stomach - by using samples of deceased cows, a stomach tube, or by cannulation.
Mr Newbold said that cannulation gives direct access to the cow's stomach, known as the rumen "so people can take out samples".
He said: "It's becoming less popular because there are laboratory models of the rumen. They are plastic but they mimic the fermentation in a cow."
"It's an operation normally done under anaesthetic, but once the animal has recovered it tends to live far longer than the average cow. It suffers pain during the process but I'm aware of animals living 12 - 15 years after the operation has been done.
Sourches Experimental Farm is owned by Sanders, a animal feed provider and subsidiary of the food group Avril. Avril told the AFP news agency that the procedure had been used for "many years in research on animals". It said the method was currently being used on six cows.
It said that the aim is to "improve the digestive health of millions of animals, reduce the use of antibiotics, and lower the nitrate and methane emissions linked to livestock farming".
Criticism from animal rights groups
In the video, L214 said: "They have pierced a hole into the cow's stomach so they can regularly access its content. Employees come regularly to open the porthole to deposit food samples or take them out. The aim is to perfect the most effective form of feeding so the cows produce as much milk as possible."
The group has launched a petition to end the practice. Brigitte Gothière, co-founder of L214 said: "Today from genetic selection to food, everything is optimised for animals to produce more eggs, milk or meat.
"Many of them already suffer from lameness, infections, lung or heart problems. And yet, instead of stopping this cycle, we are always pushing further. It is high time to put this unfair system into question."
France is Europe's second largest milk producer after Germany. It has some six million dairy cows housed at more than 61,000 dairy farms.