article_snippet: The lower frequency 'voices' of stallions tended to be associated with larger males, who had a calmer temperament and The lower frequency 'voices' of stallions offspring tended to survive for longer.
article_snippet: The researchers say the findings could also be used to help horse breeders select the best stallions for mating in the future.
article_snippet: Professor Alban Lemasson, a biologist at the University of Rennes in France, said: 'The lower pitched the stallion's voice, the slower its heart beat and the higher its reproductive success. '
article_snippet: In a study published in the journal Public Library of Science One, Professor Lemasson and his colleagues recorded the calls of 15 breeding stallions from stud farms around France.
article_snippet: male horses took blood and sperm samples from each of the horses and measured male horses heart beat.
article_snippet: male horses then played the recordings to 40 adult mares aged between seven and 27 years old at the Haras National du Pin in France.
article_snippet: Male stallions also had slower heart beats, meaning Male stallions were calmer and fewer of Male stallions offspring tended to die before or shortly after birth.
highlights_snippet: Scientists at the University of Rennes, France, recorded stallions' whinnies .
  
highlights_snippet: Male horses with deeper voices were large, calmer and had higher fertility .
  
highlights_snippet: Scientists say the findings could help horse breeders pick better stallions .