Complex sentence: Anselmo was brought back to stud at the age of 21 when a lack of stallions after World War II led to concerns that the line would not survive and produced several stallions who are represented in all Haflinger breeding populations worldwide.
Split into simpler sentences: Anselmo was brought back to stud at the age of 21 when a lack of stallions after World War II led to concerns that the line would not survive. After being brought back to stud, he produced several stallions who are represented in all Haflinger breeding populations worldwide.