All the Lassies were actually male dogs because female collies tend to "blow coat" (go through a massive hormone-induced shedding process) with each heat cycle. While males blow coat as well in reaction to a change in season, it is much less noticeable than what occurs with an intact female. By the time that spaying, which would reduce the dramatic shedding of the female, became commonplace, it had become tradition to use a male in the role. Additionally, it was believed that males, who often outweigh their female counterparts by as much as fifteen pounds, would look more impressive on film.
This was one of the first long-running television shows to remain in its time slot and day of the week during its entire prime-time run on a US television network. It became a syndicated program for the last three years of its run.
The only program to regularly bump "Lassie" off the air in the USA was the annual CBS television showing of The Wizard of Oz, which, from 1959 to 1967, always took place on a Sunday evening.
Pal, the first ever dog to play the legendary dog "Lassie" in Lassie Come Home, appeared in the pilot of this TV series (broadcast as the first two episodes). It was his last appearance before his death in 1958.
Although it has been the subject of many spoofs and misquotes, the one situation that Timmy never needed saving from in the entire history of the show was falling down a well.
The famous "whistle" theme associated with the show's opening and closing credits was not actually introduced until Season 5. The previous four seasons used a more traditional orchestral theme for its opening and closing music.