Of all Easter symbols, the lamb is probably the most strongly Christian. Other than the fact that lambs are young animals born in springtime, it has no strong ties to pagan traditions.
The lamb comes from the Jewish Passover, where each family killed a lamb as a sacrifice. When Christ became the Passover Lamb for everyone, the lamb became a symbol for His sacrifice. It is usual for the Pope to have roast lamb on Easter Sunday.
Early Christians also saw the lamb as a symbol of Jesus and used it for Easter celebration. Many people serve lamb as part of the Easter feast.