Ata bin Abi Rabah (may Allah have mercy on him) narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the sacrificial animals are of eight kinds (male and female): camels, cows, goats and sheep, according to one's means; the bigger it is, the better it is.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10150