By Jon Herskovitz

JOHANNESBURG (Reuters) - A South African province home to thousands of elephants is planning a birth control campaign for the pachyderms to prevent a population explosion that could threaten plants and wildlife.

Unlike other parts of Africa where elephant stocks have dwindled to dangerously low levels due to poaching and a loss of habitat, South Africa has seen its populations steadily grow through conservation, with the country pressed for room to house the massive animals with hefty diets.

KwaZulu-Natal province, in the southeast, is looking to expand a project running for more than a decade where elephants populations have been controlled by injecting cows with a vaccine that triggers an immune system response to block sperm reception.

"Slowing the growth rate will allow time to be gained to achieve other biodiversity objectives, such as land expansion, without having to cull the elephants," said Catherine Hanekom, an ecologist for Ezemvelo KZN Wildlife.

South Africa, which had just over 100 elephants nearly a century ago, now has more than 20,000, studies said.

The overpopulation problem is the most dire in neighboring Botswana, home to at least 133,000 elephants, where vast forests have been lost to satiate their appetites. With a human population of 2 million, it has the highest elephant-to-people ratio in Africa, at one for every 14 people.

Adult elephants consume about 100 to 300 kgs (220 to 660 pounds) of food a day and most elephants in South Africa are in fenced-in reserves where vegetation could be decimated if populations grow too large.

"Because we have taken away opportunities, they don't have the chance to remedy the overpopulation naturally as they would through migration," said Audrey Delsink Kettles, an elephant ecologist who has been leading studies for years on contraception at Makalali Private Game Reserve.

Testing of the vaccine, administered by dart and requiring an annual booster, has been conducted at 14 small reserves. Studies have shown it is reversible, nearly 100 percent effective and has no adverse impact on elephant health or behavior, Kettles said.

Contraception is seen as a humane alternative for controlling populations over the other main options of culling herds or moving them vast distances to areas with more food.

The Humane Society of the United States and Humane Society International have backed the vaccine.

"Failure to control the reproduction of the species ... leads to a population that exceeds the carrying capacity of the reserve and to habitat degradation," they said in statement.

(Reporting by Jon Herskovitz, editing by Paul Casciato)

Also on HuffPost:

Loading Slideshow...
  • An Asian elephant takes a sandshower at the zoo in Krefeld, Germany, 05 July 2012. A light coating of sand on the back acts as sunscreen and provides some cooling. AFP PHOTO / ROLAND WEIHRAUCH

  • Nelly the elephant kicks the ball in the Italian goal at the Serengeti-Park in the northern German city of Hodenhagen on June 25, 2012 . Nelly already predicted the previous German matches correctly. AFP PHOTO / HOLGER HOLLEMANN

  • An Asiatic elephant baby stands next to its mother in their enclosure in Berlin, on May 10, 2012. The young elephant was born on May 8, 2012 und is not given a name yet. AFP PHOTO / STEPHANIE PILICK

  • Juvenile elephants play in the river at the Pinnawela Elephant Orphanage in Pinnawela on June 10, 2012. Sri Lanka's main elephant orphanage staged its biggest mass christening June 10 by naming 15 baby elephants born in captivity, an official said. Thirteen babies born last year and the other two in 2010 were given names chosen from among thousands suggested by visitors to the Pinnawala orphanage. AFP PHOTO/Ishara S. KODIKARA

  • A Baby elephant explores the open-air enclosure at the zoo in Berlin, Germany, on June 5. The elephant baby was born on May 31. AFP PHOTO / SEBASTIAN KAHNERT

  • Citta, a 33-year-old female elephant reacts after she chose a melon above a sign indicating a win for the Poland football team at Krakow zoo on June 6, 2012 at the zoo in the southern Polish city of Krakow. Citta was given the option to choose between a win for the Poland football team, the Greek team or a draw between the two, for their first round Euro 2012 football championships match on June 8, 2012. Zoo organisers arranged melons over signs for both teams, so that the first melon she ate would signal her prediction of a win for that team or a draw if she chose the melon above the middle 'draw' sign. A similar stunt was perfomed for the 2010 South Africa football world cup and 2010 European football Championships in Austria and Switzerland when Paul the octopus using a similar system stunned organisers by correctly predicting all 7 of Germany's world cup games and the final match. AFP PHOTO/ CARL DE SOUZA

  • Elephants 'Shahrukh' (R) and 'Shanti'play with a ball at Hagenbecks Tierpark in Hamburg, northern Germany, on June 8, 2012. The elephants 'Shahrukh' and 'Shanti' act as a soccer oracle and picked Germany as the winner of the Euro 2012 matchup Germany versus Portugal. AFP PHOTO / ANGELIKA WARMUTH

  • An female elephant born on May 29, 2012, stands near her mother on June 18, 2012 at the Pont-Scorff zoo, western France. Weighing 70 kg, the young animal should gain a kilogramme each day during the first year, said Nicolas Chatelain, manager at the zoo. AFP PHOTO / FRED TANNEAU

  • Elephants are pictured at the Pinnawela Elephant Orphanage in Pinnawela on June 10, 2012. Sri Lanka's main elephant orphanage staged its biggest mass christening June 10 by naming 15 baby elephants born in captivity, an official said. Thirteen babies born last year and the other two in 2010 were given names chosen from among thousands suggested by visitors to the Pinnawala orphanage. AFP PHOTO/Ishara S. KODIKARA

  • BERLIN, GERMANY - MAY 10: A baby Asian elephant, born only two days before, seeks his mother's breast in his enclosure at Tierpark Berlin zoo on May 10, 2012 in Berlin, Germany. The male elephant calf, who does not have a name yet, weighs 102kg and is 91cm tall. (Photo by Sean Gallup/Getty Images)

  • A asian elephant takes a sandshower at the zoo in Krefeld, western Germany, on July 5, 2012. The sand protects the animals back. AFP PHOTO / ROLAND WEIHRAUCH

  • SYDNEY, AUSTRALIA - JUNE 27: 'Pak Boon' the female elephant makes a paint print on a canvas at Taronga Zoo on June 27, 2012 in Sydney, Australia. Taronga and Western Plains Zoo today pledged a a new elephant conservation project in Thailand and animals at Taronga made their pledge by dipping their feet and hands in paint and smudging them on canvas. (Photo by Cameron Spencer/Getty Images)

  • Donna, a two-year-old elephant, sprays water in her mouth after playing a game of football with her keepers at Whipsnade Zoo near Dunstable, central England on May 28, 2012. The elephants were playing with the ball with their keepers as the zoo prepares to host a sporting extravaganza. AFP PHOTO / ADRIAN DENNIS

  • Nelly the elephant kicks the ball in the Italian goal at the Serengeti-Park in the northern German city of Hodenhagen on June 25, 2012 . Nelly already predicted the previous German matches correctly. AFP PHOTO / HOLGER HOLLEMANN

  • Elephant keeper Gary Miller (R) holds up a canvas showing the painted footprint of female elephant Pak Boon (C) at Taronga Zoo on June 27, 2012. Over the past weeks keepers have been collecting the paw, hand, flipper and hoof-prints of some of the 4,000 animals at Taronga and Taronga Western Plains Zoos before the announcement, on June 27, of Taronga's commitment to an elephant protection project in Thailand's Kui Buri National Park. AFP PHOTO / Greg WOOD

  • MKOMAZI, TANZANIA - JUNE 19: A five month old orphaned elephant called 'Tembo' being taken for a walk by his keeper at Tony Fitzjohn's Mkomazi rhino sanctury on June 19, 2012 in Mkomazi, Tanzania. The Aspinall Foundation along with the Tusk Trust and the George Adamson Trust combined forces to stage a rare translocation of three captive born black rhino to Mkomazi National Park in Tanzania in order to rejuvenate numbers of the black rhino in the area. The three animals, Grumeti, Monduli and Zawadi were airlifted in a dedicated DHL Boeing 757 from Manston Airport in Kent direct to Kilimanjaro Int Airport in Tanzania. The rhino have been donated by Damian Aspinall, Chairman of The Aspinall Foundation, from their breeding group at Port Lympne Wild Animal Park in Kent. The reintroduction of endangered species to the wild to assist breeding programmes is a major focus of The Aspinall Foundation. Prince William as Patron of Tusk Trust and a dedicated campaigner against poaching visited the rhinos at Port Lympne ahead of their translocation and today released a speech via the BBC highlighting his dedication to the fight against the illegal trade of ivory. (Photo by Chris Jackson/Getty Images)

  • An female elephant born on the end of May 29, 2012, stands near her mother on June 18, 2012 at the Pont-Scorff zoo, western France. Weighing 70 kg, the young animal should gain a kilogramme each day during the first year, said Nicolas Chatelain, manager at the zoo. AFP PHOTO / FRED TANNEAU

  • Elephants 'Shahrukh' (R) and 'Shanti' eat fruits and vegtables decorated as a German flag with honeymelons and aubergines at Hagenbecks Tierpark in Hamburg, northern Germany, on June 8, 2012. The elephants 'Shahrukh' and 'Shanti' act as a soccer oracle and picked Germany as the winner of the Euro 2012 matchup Germany versus Portugal. AFP PHOTO / ANGELIKA WARMUTH

  • A Baby elephant stands between it's mothers legs at the open-air enclosure at the zoo in Berlin, Germany, on June 5. The elephant baby was born on May 31. AFP PHOTO / SEBASTIAN KAHNERT

  • CHESTER, ENGLAND - MAY 22: Baby elephant Nayan, aged two, gets cooled off with water by keepers at Chester Zoo on May 22, 2012 in Chester, England. As parts of Britain bask in temperatures up to 25c the herd of Indian elephants at Chester Zoo enjoyed a cool shower courtesy of the keepers and a hosepipe. (Photo by Christopher Furlong/Getty Images)

  • A herd of wild elephants from the nearby Rani forest reserve are seen in wetlands at Mikir village in the outskirts of Guwahati on May 19, 2012. At least 25 wild elephants were sighted foraging for food in the wetlands late May 18. AFP PHOTO/STR

  • BERLIN, GERMANY - MAY 10: A female, 18-year-old Asian elephant named Nova sniffs at visitors with her trunk in her enclosure at Tierpark Berlin zoo on May 10, 2012 in Berlin, Germany. Nova gave birth to a male calf two days before that today weighs 102kg and is 91cm tall. (Photo by Sean Gallup/Getty Images)

  • BERLIN, GERMANY - MAY 10: A baby Asian elephant, born only two days before, explores his enclosure at Tierpark Berlin zoo on May 10, 2012 in Berlin, Germany. The male elephant calf, who does not have a name yet, weighs 102kg and is 91cm tall. (Photo by Sean Gallup/Getty Images)

  • In this photo taken Tuesday Oct. 9, 2012 seven-and-a-half month old orphaned elephant calf named Moses reacts with one of his carers, at his home in Lilongwe, Malawi. Moses was found alone and close to death in the Vwaza Wildlife Reserve. He has been adopted by the Jumbo Foundation where he is cared for and is being raised by humans. (AP Photo/Denis Farrell)