Destriers refers to warhorses, a term that evokes a sense of medieval chivalry and power. It's a much more evocative and less common word than simply "chevaux" (horses).
In the song, the phrase "infidèles destriers" (unfaithful warhorses) is used metaphorically. It suggests that the women in the song, who are passionate about horses, eventually find that their equine companions, or perhaps the dreams associated with them, are not as steadfast as they once believed, leading them to consider other paths or "riders" in their lives.
Have you ever dreamed of something so intensely as a child that it shaped your whole life? MPL's "Infidèles Destriers" [Unfaithful Steeds] tells the story of girls who fall in love with horses from a young age, starting with plastic ponies and posters on their bedroom walls. They spend their Wednesdays at the stables, dreaming of "grandes chevauchées dans des plaines indiennes" [great rides in Indian plains].
But as they grow older, the song takes a turn. The lyrics suggest that their deep connection with horses might be holding them back from other experiences, especially romantic relationships. The repeated chorus, "Allez, jetez vos cravaches, mesdames / Pour une fois osez le cavalier / Au diable, vos infidèles destriers" [Come on, throw away your whips, ladies / For once, dare to try the rider / To hell with your unfaithful steeds], is a blunt call to embrace human connection. It's a bittersweet look at how childhood passions can become lifelong obsessions, sometimes at the expense of other desires, even leading to a sense of regret and loneliness as they realize "les bons chevaux se font rare" [good horses are rare] and they've missed out on other paths.