If the flock is lambed on the range, assistance is not given to individual ewes. Catching those needing help causes so much disruption of ewes with normal lambs and results in so many orphans, it is detrimental. One of the primary advantages of shed lambing a range flock is being able to better assist during birth and those first crucial hours of life.
Bagley, Clell, "Dystocia (Difficult Lambing)" (1997). All Current Publications. Paper 464.