Romanian emergency teams managed to save 26 sheep on Tuesday, two days after a vessel carrying 14,600 animals sank off the Romanian coast.
Emergency department official Raed Arafat said 75 sheep had now been rescued from the Queen Hind, which capsized on Sunday after setting out from Midia on the Black Sea bound for Saudi Arabia.
Officials gave no estimate for how many of the remaining sheep could have survived, though an animal welfare group said it was unlikely many more would be saved.
Arafat said the rescue effort would continue "tonight, tomorrow and the day after tomorrow... if the weather and the situation allows".
"Tonight we'll cut some holes in the ship so we can enter from more access points and save more animals," he said during a visit to Midia.
Kuki Barbuceanu, president of the Animal Rescue and Care charity, said he and his volunteers had been helping the rescue effort and had found "some 300 dead animals".
He said most of them had been in the water and it was likely they had fallen when the ship listed.
"I think a maximum of 100 sheep can be saved from now on," Barbuceanu said, adding: "The operation could have been better if the intervention was faster. Thousands could have been saved."
It has not been possible to move the ship back towards port yet as it is still listing.
The crew of 20 Syrians and one Lebanese aboard the Queen Hind were rescued after the accident, the cause of which is still not clear.
It has drawn fresh attention to the controversial sea transport of livestock.
In July, the European commissioner in charge of health and food safety demanded that Bucharest stop the transport of 70,000 sheep to the Gulf because of animal welfare concerns.