Andrew Thomas pleaded guilty after DNA tests were used to prove lambs born to stolen ewes had been fathered by rams on the victim's land in Carmarthenshire.
The 39-year-old farmer was ordered to pay Â£1,000 in compensation.
Dyfed-Powys Police said this was the first time animal DNA evidence had been used in Wales in relation to stolen sheep.
Swansea Crown Court heard 18 sheep were sold at Llanybydder market two weeks after about 50 sheep were stolen from Alan Price's land at Derwydd near Llandybie.
Mart officials and farmers became suspicious of Thomas, from Garnant, after it became clear that the sheep's earmarks had been tampered with.
Judge Geraint Walters said the "farming community had pulled together to defeat those who seek to deceive it".
He sentenced Thomas to an eight month jail term, suspended for two years.
Judge Walters told him he had "caused a great deal of hurt and had stolen from those he worked alongside," and it would be "long time before they forgave him".
A man has been given a suspended prison sentence for handling stolen sheep.