Master of Science / Department of Animal Sciences and Industry / Terry Houser / Crossbred yearling steers (n = 144 initial BW 367 ± 18.46 kg) were randomly allotted by BW to a randomized complete block design with a 2x3 factorial treatment arrangement to 1) assess the impact of supplementing dried distiller grain with solubles (DDGS) while grazing late season forage for 90 d and 2) the impact of a short feeding period on animal performance, carcass characteristics and meat quality traits. Treatments consisted of DDGS supplementation during grazing (0 or 1% of BW as DDGS; DM basis) and finishing days on feed (DOF;75, 100, 125). During grazing supplemented cattle had greater (P < 0.01) ADG than un-supplemented cattle but un-supplemented cattle had greater ADG than supplemented cattle during the finishing period. There were no differences between grazing treatments for DMI (P = 0.91) during the finishing period. Supplemented cattle had decreased (P = 0.02) G:F during the finishing period compared to un-supplemented cattle. Supplemented cattle had heavier (P < 0.01) HCW and larger (P = 0.02) LM area than un-supplemented cattle. Increasing DOF linearly increased (P ≤ 0.03) HCW, 12th rib fat thickness, LM area and USDA marbling score. No differences were observed for USDA yield grade. Increasing DOF decreased (Linear; P < 0.01) carcass protein %, moisture %, and increased (Linear; P < 0.05) carcass fat %. Increasing DOF increased (Quadratic; P = 0.01) L* values, while decreasing (Quadratic; P < 0.01) a* and b* values for external fat color. No differences were observed with respect to the percentages of any fatty acids for any treatment. Increased (P = 0.01) sensory off-flavors were present at 100 DOF when compared to 125 DOF. No other differences among treatments were observed for any sensory traits, instrumental tenderness, lean color or fatty acid profile for any treatment. In conclusion, supplementing cattle with 1 % DDGS during grazing altered grazing and feedlot performance as well as impacted carcass characteristics. In addition, utilizing a shortened feeding period had minimal effects on meat quality traits, but increasing DOF resulted in a greater amount of whiter external fat.

Three interrelated genes postulated to affect economically important traits related to growth and/or carcass quality of beef cattle were chosen to characterize and perform association analyses for this study. Melanocortin 1 receptor (MC1R), melanocortin 4 receptor (MC4R) and agouti related protein (AGRP) play an integral role in the appetite pathway and in fat deposition.<p> We genotyped 328 crossbred steers of various coat colours that were purchased at weaning and fed until slaughter for the previously published alleles ED, E+ and e. The E+ allele was present at five percent in this population and therefore was not included in further analysis. Black cattle of ED/ED or ED/e genotype had increased backfat (P<0.05) and required significantly fewer days (15-25) (P<0.01) on feed to reach a target fat level for slaughter compared to the red cattle. Red cattle of e/e genotype were found to have significantly larger longissimus dorsi (l. dorsi) area, shipping weight and hot carcass weight. Subsequent analysis revealed that the differences were comparable whether black versus red coat colour or MC1R genotype was used as the criteria for the group of cattle.<p> MC4R sequence was obtained from 20 random crossbred steers. In addition to several previously published polymorphisms, a novel Ser330Asn polymorphism was detected. A population of 382 crossbred Canadian steers and 985 crossbred American steers was genotyped for this Ser330Asn polymorphism. A minor allele frequency of 0.01 was observed in the Canadian and 0.02 in the American steer populations. No homozygous g.989AA cattle were detected. In the Canadian population, heterozygous steers had increased grade fat (P=0.036) and decreased lean meat yield (P=0.032). Similarly in the American population, steers of the g.989GA genotype had increased backfat (P=0.031) and less desirable yield grades (P=0.022,) but also lower ribeye area measurements (P=0.031). These results suggest that genotyping for the Ser330Asn polymorphism may lead to increased quality of carcasses either through lean meat production or backfat measurements, depending on the goal of the beef operation.<p> Sequence data obtained from 38 Bos taurus beef cattle, 4 Holsteins and 4 Bos indicus cattle revealed six polymorphisms in the AGRP gene. No polymorphisms that altered amino acids were detected in Bos taurus cattle. Genotyping of 382 crossbred beef steers was performed for two polymorphisms, an intronic deletion (g.439_440delTC) and a base pair substitution in exon 4 that did not alter an amino acid (g.715G>A). An ANOVA analysis, using PROC Mixed, was performed for both polymorphisms on several growth and carcass traits. No significant differences were observed.<p> Polymorphisms in MC1R and MC4R could be used as genetic tests which may be beneficial for beef producers in North America. The significant differences observed in this study in relation to cattle growth and fat deposition would represent savings for producers when used for sorting feedlot cattle or in selection of breeding cattle.

Three interrelated genes postulated to affect economically important traits related to growth and/or carcass quality of beef cattle were chosen to characterize and perform association analyses for this study. Melanocortin 1 receptor (MC1R), melanocortin 4 receptor (MC4R) and agouti related protein (AGRP) play an integral role in the appetite pathway and in fat deposition.<p> We genotyped 328 crossbred steers of various coat colours that were purchased at weaning and fed until slaughter for the previously published alleles ED, E+ and e. The E+ allele was present at five percent in this population and therefore was not included in further analysis. Black cattle of ED/ED or ED/e genotype had increased backfat (P<0.05) and required significantly fewer days (15-25) (P<0.01) on feed to reach a target fat level for slaughter compared to the red cattle. Red cattle of e/e genotype were found to have significantly larger longissimus dorsi (l. dorsi) area, shipping weight and hot carcass weight. Subsequent analysis revealed that the differences were comparable whether black versus red coat colour or MC1R genotype was used as the criteria for the group of cattle.<p> MC4R sequence was obtained from 20 random crossbred steers. In addition to several previously published polymorphisms, a novel Ser330Asn polymorphism was detected. A population of 382 crossbred Canadian steers and 985 crossbred American steers was genotyped for this Ser330Asn polymorphism. A minor allele frequency of 0.01 was observed in the Canadian and 0.02 in the American steer populations. No homozygous g.989AA cattle were detected. In the Canadian population, heterozygous steers had increased grade fat (P=0.036) and decreased lean meat yield (P=0.032). Similarly in the American population, steers of the g.989GA genotype had increased backfat (P=0.031) and less desirable yield grades (P=0.022,) but also lower ribeye area measurements (P=0.031). These results suggest that genotyping for the Ser330Asn polymorphism may lead to increased quality of carcasses either through lean meat production or backfat measurements, depending on the goal of the beef operation.<p> Sequence data obtained from 38 Bos taurus beef cattle, 4 Holsteins and 4 Bos indicus cattle revealed six polymorphisms in the AGRP gene. No polymorphisms that altered amino acids were detected in Bos taurus cattle. Genotyping of 382 crossbred beef steers was performed for two polymorphisms, an intronic deletion (g.439_440delTC) and a base pair substitution in exon 4 that did not alter an amino acid (g.715G>A). An ANOVA analysis, using PROC Mixed, was performed for both polymorphisms on several growth and carcass traits. No significant differences were observed.<p> Polymorphisms in MC1R and MC4R could be used as genetic tests which may be beneficial for beef producers in North America. The significant differences observed in this study in relation to cattle growth and fat deposition would represent savings for producers when used for sorting feedlot cattle or in selection of breeding cattle.