Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: V. Postweaning growth, feed intake, and feed efficiency.

This study was conducted to quantify differences in feed efficiency among 4 sire breeds using records from 1,109 crossbred lambs over 3 yr. Lambs were produced from mating Columbia, USMARC-Composite (Composite), Suffolk, and Texel rams to adult Rambouillet ewes. After weaning, lambs were finished on a high-energy diet in group-fed pens. Efficiency was assessed at 45 and 90 d on study, 50 and 60 kg of BW, and 6.6 and 9.1 mm of fat depth between the 12th and 13th ribs. Sire breed affected most of the traits that were measured. At 90 d, Suffolk-sired lambs had gained 13 to 19% more BW (P < 0.001), were 7 to 13% heavier (P < 0.001), and had consumed 4 to 11% more (P < 0.001) ME than the other breed crosses. However, at 90 d, G:F (59.9 vs. mean of 56.2 g BW gain/Mcal of ME; P < 0.01) and residual BW gain (RG; 0.94 vs. -0.33 kg BW; P < 0.05) were greater for Suffolk-sired lambs than for the other 3 sire breeds. Also, RG for Suffolk-sired lambs was greater (P < 0.01) at 6.6 and 9.1 mm of fat depth (0.62 vs. -0.24 kg and 0.87 vs. -0.33 kg of BW, respectively) and at 60 kg of BW (0.73 vs. 0.31 kg of BW) than for the other sire breeds. At 90 d, Columbia-sired lambs had the greatest (P < 0.01) residual feed intake (RFI; 7.01 vs. mean of -2.33 Mcal ME for the 3 other sire breeds). At 60 kg of BW, Texel- and Composite- (-2.34 Mcal ME, combined) had more favorable (P < 0.01) RFI than Columbia-sired lambs (6.42 Mcal ME), and Suffolk-sired lambs (0.49 Mcal ME) were intermediate and not different from the other 3 sire breeds. At 6.6 mm of fat depth, Columbia- and Suffolk- (3.30 Mcal ME, combined) had greater (P < 0.001) RFI than Texel-sired lambs (-4.23 Mcal ME); at 9.1 mm of fat depth, Columbia-sired lambs had the greatest (P < 0.05) RFI (7.35 vs. -2.11 Mcal ME for the other breeds combined). In summary, except for ME intake at 90 d, Suffolk-sired lambs were equal or superior to Columbia-, Composite-, and Texel-sired lambs for BW, BW gain, ME intake, G:F, RFI, and RG to 90 d, 60 kg of BW, and 9.1 mm of fat depth. Breed rankings were consistent across the study period for G:F and RG, but rankings changed over time for RFI.

Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: II. Postweaning growth and ultrasonic measures of composition for lambs fed a high-energy feedlot diet.

Over 3 yr, postweaning growth patterns and changes in ultrasonic measurements of fat depth (FD) and LM area were assessed for 1,049 crossbred ewe and wether lambs (Ovis aries) produced by mating adult Rambouillet ewes to 1 of 22 Columbia, 22 USMARC-Composite (Composite), 21 Suffolk, or 17 Texel rams and raised to weaning under extensive Western rangeland conditions. After weaning, lambs were transitioned to a high-energy finishing diet in a feedlot, weighed weekly for 13 to 16 wk, and scanned using ultrasound at 2-wk intervals to estimate FD and LM area between the 12th and 13th ribs. Lambs sired by Suffolk rams were 5 to 12% heavier (P < 0.05) at start of test, grew 14 to 22% faster (P < 0.001), and were correspondingly 7 to 14% heavier (P < 0.001) after 90 d on test than lambs sired by rams of the other 3 breeds. At this time, lambs sired by Texel rams were 5% lighter (P < 0.01) than Columbia- or Composite-sired lambs, which did not differ (P > 0.20). Columbia-sired lambs had less FD (8.9 mm) but smaller LM areas (15.6 cm(2)) at 90 d on test (both P < 0.01) than lambs sired by rams of the other breeds (average of 9.8 mm for FD and 16.6 cm(2) for LM area), which did not differ for either measurement at this time. At 60 kg, predicted FD differed among sire breeds (P < 0.001) and were similar for Suffolk- (7.6 mm) and Columbia-sired (7.9 mm) lambs, intermediate for Composite-sired lambs (9.1 mm), and largest for Texel-sired (10.1 mm) lambs. At a BW of 60 kg, LM area differed between all pairs of sire breeds (P < 0.05), and was largest for Texel-sired lambs (16.7 cm(2)), followed by Composite-, Suffolk-, and Columbia-sired lambs (15.7, 14.8, and 14.5 cm(2), respectively). At a predicted FD of 9.1 mm (the boundary between U.S. Yield Grades 3 and 4), the predicted LM area for Suffolk-sired lambs (16.2 cm(2)) was similar (P > 0.10) to that of Texel-sired lambs (16.0 cm(2)) and superior (P < 0.01) to that of Composite- (15.7 cm(2)) and Columbia-sired lambs (15.4 cm(2)). Lambs sired by Suffolk rams were thus equal or superior to lambs sired by the other 3 breeds in growth, FD, and LM area at comparable ages, fatness at 60 kg, and LM area at a FD of 9.1 mm, but inferior in LM area to Texel- and Composite-sired lambs at comparable BW.

Identifying differences in feed efficiency among group-fed cattle.

Identification of efficient animals in the postweaning growth phase for use in selection for improved feed efficiency is important to improve the economic and environmental sustainability of the beef cattle industry. Progeny testing using group-fed animals in commercial feedlots is the most common and practical method used to evaluate postweaning growth on large numbers of animals. We developed the Cornell Value Discovery System (CVDS) to dynamically predict growth rate, accumulated weight, days required to reach target body composition, carcass weight, and composition of individual beef cattle fed in group pens. Observed BW, ADG, BW at 28% empty body fat (EBF), breed type, environmental conditions, and dietary ME concentration are used by the CVDS to predict, for each animal in a pen, the feed DM required for maintenance (FFM), the feed DM required for gain, and the total DM required for maintenance and gain (DMR). The CVDS then computes DMR-to-ADG ratio (DMR:ADG), which is a feed conversion measure, and ADG-to-DMR ratio (ADG:DMR), which is a feed efficiency measure, for each animal. This study used the observed F:G ratio of 362 individually fed steers to evaluate CVDS-predicted indicators of feed efficiency and the Kleiber ratio. A subset of 37 data points was used to evaluate residual feed intake (RFI) as an indicator of feed efficiency. The database included 4 published studies, each with detailed individual animal description, environment, diet, and body composition information. The CVDS-predicted DMR:ADG accounted for 84% of the variation in the actual F:G ratio with a mean bias of 1.94% (P = 0.20). The predicted FFM to actual DMI ratio had a high correlation with actual ADG (R2 = 0.76), and indicated a decay-type nonlinear dilution of FFM as ADG increased. The CVDS-predicted ADG:DMR and the Kleiber ratio had a significant (R2 = 0.88) logarithmic relationship. In an analysis of a contemporary group within the database, RFI was highly correlated with the F:G ratio (r = 0.71). There was a positive relationship between RFI and EBF. The RFIM (DMI - DMR) was moderately correlated with DMI and ADG (0.37 and -0.38; respectively), suggesting that selecting for low RFI(M) would decrease DMI and increase ADG in this database. We conclude that the CVDS model can be used to identify differences in the F:G and G:F ratios by predicting DMR for individual growing cattle fed in groups.