3n+ 1y = 1000 2

4y+ 1z = 1000 3

1 equation times 3

6z+3n = 3000……4

Equation 4- Equation 2

6z-y = 2000 5

5 equation multiplied by 4

24z-4y = 8000 6

Equation 3+ Equation 6

25z=9000

Get z=360.

Substituting 1 gives n=280.

Substitute 2 to get y= 160.

There are 2 pigs, 3 cows and 4 sheep, and the total price is less than 1000 yuan. It's no use.

Answer: pig 360 cattle 280 sheep 160.