SYDNEY, May 9 (Xinhua) -- Captive breeding programs to save endangered animals from extinction may be doing them more harm than good, with the captivity significantly impacting their internal organs, according to latest Australian research.

The findings could have implications for the breeding programs, particularly when animals are reintroduced into the wild, as the internal problems would mean they would be less likely to survive than wild-born animals, the researchers from the University of New South Wales and University of Wollongong said in a statement on Wednesday.

The researchers used house mice to compare captive and wild animals and, after one generation of mice in captivity, found that the captive-reared ones suffered from conditions such as lighter combined kidney and spleen masses.

The changes in the organ sizes occurring in captivity "could be due to the functional capacity of these organs being in excess of the actual demands, which would make the organs expensive and inefficient to maintain. Subsequently, the size of organs may have altered to deal with such inefficiency," said the researchers in the paper published in the Royal Society Open Science journal.

Identifying the magnitude and direction of such morphological changes in captivity is "an important first step" toward developing and refining ways to minimize negative impacts on animals in captivity, in turn improving captive breeding and reintroduction programs, they said.