Evaluation of feedlot feed efficiency relationships as well as genetic and phenotypic performance, carcass, and economic outcomes

Several feed efficiency values have recently been proposed including: feed conversion ratio in terms of feed:gain (FCR), residual feed intake (RFI), and residual BW gain (RG), and residual intake and BW gain (RIG). These all have production efficiency potential since they include feed intake inputs and production outputs. The objective of this dissertation was to investigate: 1) heterosis effects on feed efficiency, 2) how measures of feed efficiency affect one another, 3) heritability estimates, 4) genetic and phenotypic relationships of performance, carcass, economic, and feed efficiency traits and 5) the relationship of economic factors and prediction of these factors utilizing performance, carcass, and feed efficiency characteristics. Steers were all early weaned (78 ± 24 d) and managed similarly prior to weaning and in the feedlot. Steers were all of known Simmental (SM), Angus (AN), and SM x AN genetics. Steers were pen-fed and individual DMIs were recorded using the GrowSafe® automated feeding system (GrowSafe® Systems Ltd., Airdrie, Alberta, Canada). Two experiments (1: n = 612) (2: n = 158) were conducted to analyze the effect of heterosis on subsequent steer progeny. Maternal heterosis was classified by dam breed into four categories: 1) 100% AN (AN), 2) 75% AN (75AN), 3) 50% AN (50AN), and 4) 75% or greater SM (SM). Results from experiment 1 showed that ADG was 0.08 kg higher (P < 0.05) for progeny of SM compared to AN dams. Dry matter intake and consequently RFI were improved (P < 0.05) for 75AN and 50AN compared to AN and SM dams. Residual BW gain was improved in (P < 0.05) progeny of SM dams when compared to AN dams. In conclusion, dams of varying AN breed composition produced offspring that performed differently with progeny from 75AN dams excelling in the feedlot. Next, Purebred AN and SM sires and dams were utilized. Progeny of SM dams had a more desirable RFI (P < 0.05). An improved HCW, backfat, LM area, and consequently yield grade was shown by progeny of SM dams (P < 0.05); however, marbling score was 80 units higher for progeny of AN dams (P < 0.05). The only sire by dam breed interaction was for marbling score (P = 0.05). Overall, maternal heterosis effects on performance, feed efficiency measures, and carcass traits of resulting progeny appear to be important. All feed efficiency traits investigated were favorably correlated both genetically and phenotypically to one another. Feed conversion ratio was genetically correlated to RG and RIG at -0.97 and -0.95, respectively. Feed conversion ratio is highly correlated with growth traits therefore an increase in weight led to a more desirable FCR. While a phenotypic increase wasn’t significant, a genetic increase in carcass value was associated with a more desirable FCR. A similar effect was shown when utilizing RG since it is very similar to FCR. While RFI does a good job at reducing intake, but it is genetically correlated to HCW at 0.34 having the genetic potential to also reduce weight. Residual intake and BW gain combined the advantageous performance aspects of reduced DMI like RFI and increased ADG like RG. It is also moderately heritable at 0.22 ± 0.10 like its component traits. Economic characteristics are favorable toward RIG; however, it was associated with a slightly lower marbling score in this study. All feed efficiency values were correlated (P < 0.05) favorably with profit per steer. Carcass value was correlated (P < 0.05) with RG and RIG and a ten percent improvement in RIG yielded $22.55 increase in value. The model for carcass value explained 96% of the variation among carcasses and included HCW, marbling score, and yield grade. Average daily gain, marbling score, yield grade, DMI, HCW and year born constituted all 81% of the variation in the prediction of profit. Variation in cost of gain was mainly explained by ADG and DMI. Next, prediction equations were developed that excluded ADG and DMI and included feed efficiency values. Cost of gain was explained primarily by FCR (r2 = 0.71). Seventy-three percent of profitability was explained by the calculated prediction equation; RG and marbling made up 54% of this total explained variation. These models represent the relative importance of factors contributing to economic success in feedlot cattle based on current prices. In summary, feedlot feed efficiency was affected by breed composition and related to important performance, carcass, and economic characteristics of feedlot cattle. Selection for feed efficiency traits will be an important tool for lowering input costs and can lead to an increase in profitability; however, desirable performance and carcass traits are the larger determinates in profitability.

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