Length of the weaning period does not affect post-weaning growth or health of lightweight summer-weaned beef calves

Bovine respiratory disease (BRD) is the most economically devastating feedlot disease. Risk factors associated with incidence of BRD include: 1) stress associated with maternal separation; 2) stress associated with introduction to an unfamiliar environment; 3) low feed intake associated with the introduction of novel feedstuffs into the diet; 4) exposure to novel pathogens upon transport to a feeding facility and commingling with unfamiliar cattle; and 5) inappropriately administered respiratory disease vaccination programs. Management practices collectively referred to as preconditioning are thought to minimize carcass damage resulting from BRD. Preconditioning management attempts to eliminate or reduce risk factors for respiratory disease by: 1) employing a relatively long ranch-of-origin weaning period following maternal separation, 2) exposing calves to concentrate-type feedstuffs, and 3) improving resistance to respiratory pathogens through a pre-weaning vaccination program. The effectiveness of such programs for preserving animal performance is highly touted by certain segments of the beef industry. Ranch-of-origin weaning periods of up to 60 days are suggested for preconditioning beef calves prior to sale; however, the optimal length of the weaning period has not been determined experimentally. The objective of this study was to test the validity of beef industry assumptions about the appropriate length of ranch-of-origin weaning periods for summer-weaned calves aged 100 to 160 days