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Title: Relationship of feed efficiency of replacement beef heifers to subsequent feed efficiency as 3-year old suckled beef cows

Author
item BLACK, T - University Of Florida
item BISCHOFF, K - University Of Florida
item MERCADANTE, V.R. - University Of Florida
item MARQUEZINI, G.H. - University Of Florida
item Chase, Chadwick - Chad
item Coleman, Samuel
item LAMB, G - University Of Florida

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 7/10/2011
Publication Date: 7/14/2011
Citation: Black, T.E., Bischoff, K.M., Mercadante, V.G., Marquezini, G.L., Chase, C.C., Coleman, S.W., Lamb, G.C. 2011. Relationship of feed efficiency of replacement beef heifers to subsequent feed efficiency as 3-year old suckled beef cows. Journal of Animal Science Supplement. 501-502.

Interpretive Summary:

Technical Abstract: We determined the correlaton between Residual Feed Intake (RFI) measured as post-weaned growing heifers (phase 1) and RFI measured as lactating beef cows (phase 2) in the same cohort. Individual performance and daily DMI were evaluated in 74 yearling heifers, and were subsequently reevaluated upon the birth of their second calf. For both phases, a 14-d acclimation period preceded a 70 d test using the GrowSafe System (GrowSafe Systems Ltd., Alberta, Canada) to record individual feed intakes. Forage-based diets fed in both phases were formulated to support 1 kg/d in phase 1 and lactation maintenance requirements in phase 2. Cattle were weighed every 14 d and for phase 2 cows were milked on d 14 (lactation d 28 +- 7) and d 70 (lactation d 84 +-) to determine energy corrected milk (ECM) production. Fat thickness over the 13th rib (BF) and ribeye area (REA) were determined by ultrasound. Heifers were ranked by RFI and placed into Low (<0.5 SD; n = 24), Med (<0.5 SD >; n=24), and High (>0.5 SD; n=26) RFI model included d 28, d84 ECM and d 84 BF which explained 36%, 11%, and 3%, respectively, of the ariation in DMI not explained by ADG and MBW. Cows which were most efficient as heifers (Low) and lower (P<0.05) daily DMI and RFI values (13.6 +-0.6; -1.17 +- 0.5 kg/d, respectively) than cows ranked as Med (15.5 +- 0.6; 0.8 +- 0.5 kg/d) or High (15.7 +- 0.6; 0.24 +- 0.46) as heifers. In addition, cows which were least efficient as heifers (High) had the greatest d28 and d84 ECM (6.27 +- 0.36; 5.4 +- 0.31 kg/d) compared with cows that were more efficient heifers (4.66 +- 0.38 and 4.58 +- 0.33 kg/d Low; 4.66 +- 0.38 and 4.0 +- 0.33 kg/d Med). Pearson rank corrleation between heifer and cow RFI was r=0.19 (P=0.12). We conclude that ECM and BF are important sources of variation affecting evaluation of RFI in lactating beef cows and heifers ranked as more efficient subsequenlty consumed less as cows.