With their bouffant hairstyles and pin- striped suits, the millionaire sons of Donald Trump are a chip off the old block when they appear among New York's glitterati. But one area where Donald Jnr and Eric Trump don't see eye-to-eye with their father is in killing animals for fun.

The pair have been forced to defend themselves against accusations of cruelty after photographs emerged on the internet of them standing next to animals shot dead during a hunting holiday last year.

Zimbabwean conservationists and animal-rights groups have hit out at the two millionaires – and even Donald Snr has publicly questioned why his sons enjoyed hunting so much.

The photos appeared on the website of Hunting Legend, a company that specialises in tailor-made big-game hunting across Africa for wealthy clients in Europe, the Middle East and the US.

The brothers are shown in trophy photos standing next to a dead elephant, a crocodile, a kudu, a leopard and a waterbuck. The animals were all shot on a hunting range close to Zimbabwe's Victoria Falls. In one picture, Donald Jnr is holding a knife and a severed elephant tail.

Wealthy hunters pay thousands of dollars to shoot big game in Africa. The most prized hunts are the so-called "Big Five" – leopard, lion, rhino, elephant and buffalo. Four of the five are endangered. Killing one of these can often cost $10,000 (£6,300) for licences, which are meant to be strictly rationed. Hunting lodges insist animal populations need to be controlled and that the money that is generated through licences finance conservation efforts and provide employment for locals.

In a series of tweets, 34-year-old Donald Jnr defended his holiday: "I hunt and eat game. I am a hunter, I don't hide from that." In a reply to a critic he also denied that the kills were wasteful, writing: "I can assure you it was not wasteful the villagers were so happy for the meat which they don't often get to eat. Very grateful."

But many conservation groups are uncomfortable with private hunts, especially in Zimbabwe, where endemic corruption and a poor security situation means poaching and overkill is rampant whilst little money filters down to the poor. One of Zimbabwe's most eminent conservationists told The Independent yesterday that he believed private hunting should be banned for two years until a genuine count of the country's animals could be completed.

"The government deliberately overestimates how many animals we have so they can grant more licences and make more money," Johnny Rodriquez, of the Zimbabwe Conservation Taskforce, said. "If things carry on the way they have recently there won't be any animals left in the next five or six years.