Early weaning and postweaning nutritional management affect feedlot performance of Angus x Simmental heifers and the relationship of 12th rib fat andmarbling score to feed efficiency

Early-weaned Angus x Simmental heifers were used to evaluate the effects of postweaning nutritional management on feedlot performance, carcass merit, and the relationship of intramuscular and subcutaneous fat deposition to th e feed efficiency among:heifers fed for a high-quality market. Sixteen heif ers were weaned at 73 +/- 5.5 d of age and grazed on endophyte-infected tal l fescue for 18 mo before entering the feedlot (early-weaned-P). Eighty hei fers from the following year's calf crop were weaned at 71 +/- 5.5 d of age and allowed either ad libitum access to a 25% concentrate diet (early-wean ed-25C) or limit-fed a 90% concentrate diet (early-weaned-90C) to achieve a similar ADG. Following a 119-d growing period, 16 early- weaned-90C and 16 early-weaned-25C calves were paired based on BW and growth rate and indivi dually fed during the finishing period along with the early-weaned-P heifer s. Ultrasound-measurements of s.c. and i.m. fat were recorded at approximat ely 60-d intervals throughout the finishing period. Feed efficiency was reg ressed against s.c. and i.m. fat, and i.m. fat was regressed on s.c. fat. D espite a similar ADG, early-weaned-SOC calves gained more efficiently (P le ss than or equal to 0.05) in the feedlot than early-weaned-25C calves. Heif ers finished as yearlings tended (P less than or equal to 0.10) to gain fas ter but gained less efficiently (P less than or equal to 0.01) than early-w eaned-90C heifers finished as calves. The rate of s.c. and i.m. fat deposit ion was similar between early-weaned-90C and early-weaned-25C heifer calves . The calves were grouped together for comparison to yearlings. Feed effici ency decreased quadratically (P less than or equal to 0.01) as s.c. fat cov er increased. The rate at which feed efficiency decreased relative to incre asing s.c. fat cover was similar regardless of age at feedlot entry. Howeve r, heifers finished as calves gained more efficiently (P less than or equal to 0.01) than yearlings at any given fat thickness. Feed efficiency decrea sed linearly (P less than or equal to 0.01) as i.m. fat increased among hei fers finished as calves. Additionally, heifers finished as calves deposited i.m. fat at a faster rate relative to s.c. fat (P less than or equal to 0. 01) than yearlings. These data suggest that heifers finished as calves prod uce high-quality carcasses with less s.c. fat cover while gaining more effi ciently than heifers finished as yearlings.