Widespread ignorance among cat-owners about the sex lives of their pets may be leading to more than 200,000 unplanned litters -- or more than 850,000 kittens every year in the UK, finds research published online in Veterinary Record.

In fact most litters of cats born in the UK are unplanned, the findings indicate. It is thought that up to 150,000 cats in the UK ended up in animal welfare facilities in 2009-10, and that unplanned litters account for up to one in seven cats being given up for rehoming by an owner.

Unplanned litters also boost the risk of health problems for the mother cat and her kittens, including birth defects as a result of inbreeding, say the authors.

The authors base their findings on a survey of almost 10,500 UK households and more than 3000 completed returns (30% response rate).

Information was gathered on pet ownership, with specific questions asked of owners of female cats about how many planned or accidental litters their pets had had. The survey also aimed to probe the prevalence of common misconceptions about the breeding patterns of cats.

In all, data were collected from 715 cat-owning households, of which 426 owned one or more female cats. Around 1 in 8 (13%) of these owners said that their pets had had one or more accidental litters. A total of 128 litters had been produced by 91 (out of 552) female cats; 65 of these had given birth to 102 unplanned litters, meaning that just under 80% of all litters had been accidental.

Unplanned litters were more than twice as likely in households owning more than one cat and more than four times as likely if the owner mistakenly believed that a female cat should have a litter before being neutered, the responses showed. Men were more than twice as likely as women to hold this belief. The authors calculate that if this belief were dispelled, there could be around 213,000 fewer litters and more than 851,000 fewer kittens born in the UK every year.

Half (49%) of 682 cat owners surveyed believed that cats should either have a litter before being neutered (23%) or were unsure if they should (26%), despite there being no evidence whatsoever that this benefits feline health.

Similarly, among the 659 owners who answered the question about puberty, most (83.5%) mistakenly believed that the youngest age at which a cat could get pregnant was five months, with a further one in four (26%) believing that an unneutered female cat (queen) couldn't get pregnant before the age of 12 months. It's not common for a four month old kitten to get pregnant, but it does happen, say the authors.

Furthermore, one in seven cat owners incorrectly thought that unneutered related cats wouldn't mate with each other, and a further one in four (24.5%) were unsure.

"The vast majority of litters born to cats in the UK are not planned," conclude the authors. They add: "This study suggests that improving cat-owner knowledge of the reproductive capacity of cats is likely to have a significant impact on the numbers of accidental litters."

Dispelling the commonly held belief that cats should have a litter before neutering would have the single biggest impact on the figures, they suggest.