Mahabharat Book 12 Section CLXV Line says
Having slain a Vaisya one should perform such a sacrifice for two years and make a present of a hundred kine with one bull. Having slain a Sudra, one should perform such a sacrifice for one year and make a present of a hundred kine with one bull. Having slain a dog or bear or camel, one should perform the same penance that is laid down for the slaughter of a Sudra.
According to the above shloka, the penance for killing the Vaisya and Shudra are as follows:
Vaisya: penance for 2 years + 100 kine + 1 bull
Shudra: penance for 1 year + 100 kine + 1 bull
Q1: Why the penance for slaying a Shudra is less?
Q2: Why is the penance for killing a Shudra equal to the killing of a dog/bear/camel? (refer to the bold text in the shloka above)