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The effect of time of suckling calf implant (SCI) use on weaning weight (WW), post-weaning performance and subsequent carcass traits was compared in steer calves produced on one ranch in western SD. Calves were born in March and April of each year and were reared on native range prior to weaning. The SCI strategies used included: non implanted controls (NI) or implanted with Synovex C either in May (MAY), or August (AUG). Age groups of dams (≥4 years) were managed separately through the breeding seasons. At weaning (late October) all calves were weaned and relocated to the SDSU Ruminant Nutrition Center feedlot. Steers were individually weighed, vaccinated, and treated for parasites and the processing body weight recorded was considered the WW. Steers were sorted into feedlot pens by SCI treatment (8 or 9 steers/pen; 8 pens/treatment; 24 pens/yr). Steers were backgrounded and finished using diets and management typical for this region and included the use of implants uniformly across SCI treatments. Both the MAY and AUG implant treatments increased WW over non-implanted calves. The magnitude of this was response interacted with the age of the dams. Steers nursing mature cows and implanted in May had the greatest increase in WW over NI (40 lb). The WW advantage for steers nursing mature cows and implanted in August was reduced to 17 lb. Timing of implant administration had the opposite effect in young cows and was more beneficial when steers were implanted in August. The weight advantage due to suckling implants persisted through to carcass weight. The SCI treatments did not affect the post-weaning ADG or feed efficiency of the steers and had no adverse effects on Quality Grade of the carcasses produced. There was a substantial benefit to the cow calf producer to match the time of implant administration with the age of the dam with no adverse impact on overall beef production.

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