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Graduation date: 1998

Half-blood Bonsmara steers were evaluated for temperament during stressful situations to discover the relationships between behavioral stress responses, growth, carcass characteristics and tenderness. Two experiments were conducted to evaluate behavioral stress responses at different stages in the U.S. beef production system with growth, carcass characteristics and tenderness. The first experiment evaluated stress responses at both time of weaning and at the beginning of the feedlot period on half-blood Bonsmara X Beefmaster steers. Steers (n=156) were weaned and paired to destinations of either Uvalde or Overton for winter grazing. At weaning cattle were weighed, and temperament measurements were recorded. After grazing winter pastures, cattle entered the feedlot and were measured for temperament, weight, and condition and frame scores. Cattle were harvested in two groups; each group was selected for harvest when they reached a backfat of approximately 7 mm. Backfat endpoints were determined by visual assessment and ultrasound. Carcass data were recorded approximately 36 hrs post-mortem, and 2.5cm steaks were removed from the 13th rib for Warner-Bratzler shear force determination. The second experiment involved Bonsmara X Angus (n=207) steers grazed on wheat pasture and fed at Cattletown feedlot near Hereford, TX. The steers were evaluated near the beginning and end of the finishing phase for performance and temperament. They were harvested in two groups; each group was selected for harvest when they reached approximately 7 mm of backfat as determined by visual assessment and ultrasound. In experiments 1 and 2, behavioral or temperament measures and hormonal responses were related to each other. It appeared as cattle become acclimated to the production system, temperament measures lose their predictive ability. In Experiment 1, weaning exit velocity appeared to be more related to economically important traits such as ADG (r = -0.26), ribeye area (r = -0.37), and Warner Bratzler shear force (r = 0.27), although beginning feedlot exit velocity was associated with feedlot weights (r = -0.30). In Experiment 2, end feedlot measurements tended to be more associated with feedlot weight (r = -0.20), but there did not seem to be any high relationships with carcass characteristics and tenderness.

Pro-opiomelanocortin is a prohormone that codes for many different peptides, some of which are involved in the appetite pathway. A single nucleotide polymorphism c.288C>T in pro-opiomelanocortin (POMC) was previously demonstrated to be associated with hot carcass weight (HCW) and shipping weight (Ship wt) in cattle. While developing a commercial real time PCR test for the POMC c.288C>T we identified a 12 bp deletion (POMC c.293_304delTTGGGGGCGCGG). The deletion results in the removal of four amino acids; valine, two glycine, and alanine. The deletion does not cause a frame shift. Both the POMC c.288C>T SNP and the deletion were genotyped in 386 crossbred steers, and evaluated for associations with carcass traits. The animals with one copy of the deletion had a significantly lower end-of-background rib-eye area (P=0.04) and carcass rib-eye area (P=0.03) when compared to animals without the deletion. A significant association with the POMC c.288C>T SNP was found with start of finishing weight (SOF WT); (P=0.04), HCW (P=0.02), average fat and grade fat (P=0.05), carcass rib-eye area (REA); (P=0.03) and marbling (P=0.02). These results suggest that it would be beneficial for beef producers to know both the deletion and the POMC c.288C>T SNP genotypes when making marketing and culling decisions.

Pro-opiomelanocortin is a prohormone that codes for many different peptides, some of which are involved in the appetite pathway. A single nucleotide polymorphism c.288C>T in pro-opiomelanocortin (POMC) was previously demonstrated to be associated with hot carcass weight (HCW) and shipping weight (Ship wt) in cattle. While developing a commercial real time PCR test for the POMC c.288C>T we identified a 12 bp deletion (POMC c.293_304delTTGGGGGCGCGG). The deletion results in the removal of four amino acids; valine, two glycine, and alanine. The deletion does not cause a frame shift. Both the POMC c.288C>T SNP and the deletion were genotyped in 386 crossbred steers, and evaluated for associations with carcass traits. The animals with one copy of the deletion had a significantly lower end-of-background rib-eye area (P=0.04) and carcass rib-eye area (P=0.03) when compared to animals without the deletion. A significant association with the POMC c.288C>T SNP was found with start of finishing weight (SOF WT); (P=0.04), HCW (P=0.02), average fat and grade fat (P=0.05), carcass rib-eye area (REA); (P=0.03) and marbling (P=0.02). These results suggest that it would be beneficial for beef producers to know both the deletion and the POMC c.288C>T SNP genotypes when making marketing and culling decisions.

Beef carcass value is influenced by the quantity and distribution of adipose tissue. Elucidation of metabolic controls of caloric partitioning between adipose depots could lead to development of production solutions that enhance beef carcass value. Historical trends in Choice and Select beef supply and short-term demand structures for Choice and Select boxed beef were explored. Recent stabilization in slaughter mix may suggest an optimum is being approached. Evaluation of short-run demand supports this premise, and suggests that Choice and Select products may not be strong substitutes. Growth-based prediction equations relating carcass traits to growth traits using ultrasound measurements as the basis of projections under different growing systems were explored. Accuracy of carcass fat predictions from growth-based equations is influenced by weight gain between ultrasound and endpoint, breed, and gender; scans out to 120 d pre-harvest may be accurate. Angus steers were used to test effects of dietary energy source on muscle and adipose tissue metabolism and insulin sensitivity. Results suggest that feeding hay limited both glucose supply and tissue capacity to increase glucose utilization in response to insulin without altering acetate conversion to fatty acids. Because subcutaneous (s.c.) adipose tissue consistently utilized more acetate and oxidized more glucose than intramuscular (i.m.), these results suggest that hay-based diets may alter i.m. adipose tissue metabolism with less impact on s.c. adipose tissue. Additionally, s.c. adipose tissue may become resistant to insulin in steers fed to an excessive s.c. fat thickness. A final experiment was designed to test the effects of dietary energy source during backgrounding and compositional endpoint on adipose tissue metabolism and insulin sensitivity. Feeding hay during backgrounding may have differential effects on tissue lipogenesis. Feeding hay increased both glucose oxidation and incorporation of acetate into fatty acids; in i.m. insulin failed to stimulate glucose conversion to lipid. As physiological maturity increases, glucose conversion to CO2 and lactate increased, but the ability of insulin to stimulate lipid synthesis from glucose may be reduced. These data provide foundation for a hypothesis regarding diet-mediated regulation of differential adipose tissue metabolism. Validation of these hypotheses could generate nutritional strategies that alter the rate and site of adipose deposition.

The objective of this study was to determine if feeding behavior traits are correlated with performance and feed efficiency traits in growing heifers. Individual dry matter intake (DMI) was measured in Brangus heifers (n = 115) fed a roughage-based diet (ME = 2.1 Mcal/kg) for 70 d using Calan gate feeders (6 heifers/pen). Residual feed intake (RFI) was computed as the residuals from linear regression of DMI on mid-test BW0.75 and average daily gain (ADG). Heifers with the highest (n = 18) and lowest (n = 18) RFI were identified for feeding behavior measurements. During days 28 through 56 of the 70-d feeding trial, continuous video recordings were obtained for all heifers. Video images of two sets of four 24-h periods, two weeks apart, were analyzed for the focal animals. All occurrences of feeding were timed and counted per day, and the eight 24-h periods averaged to derive the overall feeding event (FE) and meal duration and frequency for each focal heifer. Total feeding event duration was defined as the total min per day the animal’s head was down in the feed bunk. A meal included all visits an animal made to the feed bunk that were separated by less than 5 min. The mean RFI values for the low and high RFI heifers were (mean ± SE) - 1.03 and 1.00 ± 0.03 kg/d, respectively. Low RFI heifers consumed 21.9% less (P < 0.0001) DMI, but had similar BW and ADG compared to high RFI heifers. Heifers with low RFI spent more time (P < 0.0001) eating (152 vs 124 ± 4.26 min/d) at a lower eating rate (62.8 vs 99.6 ± 3.28 g/min), but had similar FE frequencies compared to high RFI heifers. Feeding event duration was negatively correlated with RFI while FE frequency and FE eating rate were positively correlated with RFI. However, meal duration and frequency were not correlated with RFI. Therefore, measuring FE characteristics could prove more useful than analyzing meals when trying to predict RFI. Additionally, eating rate appeared to be more closely related to RFI than any of the other feeding behavior traits measured.

A practical method of reducing aerosolized pathogens and environmental contaminants during commercial transportation could prove beneficial to the health and value of cattle. Having previously determined that there was very limited airflow within moving livestock trailers, an experimental treatment that increased cross-ventilation within commercial cattle trailers by installing aluminum scoops to punch-hole trailers was evaluated. Environmental factors including temperature, ammonia and carbon dioxide concentrations, and percent dry matter of excreted urine and fecal matter were evaluated, along with physiological factors, including complete blood count, serum electrolyte concentrations, percent weight loss, the presence of Salmonella, Escherichia coli, or Mannheimia haemolytica, and 30 day health data. The experiment consisted of two trials, each with two truckloads of 80 cattle each, for a total of 320 cattle. Temperature was evaluated in the center compartments of each trailer at five minute intervals throughout both trips. Ammonia concentrations were measured using passive dosimeters. Jugular blood samples, fecal grab samples, swabs of the terminal rectum and nasal swabs were obtained 8.5 to 10 hours post-transport from 20 cattle from each trailer. Increased ventilation resulted in lower temperatures and ammonia concentrations on both trips. Percent dry matter of excreted urine and fecal matter were inconclusive. There were no treatment effects for complete blood counts or electrolyte and basic chemistry panels, possibly because the cattle had access to both hay and water between transport and sampling, which allowed for recovery. Cattle in the ventilated trailer had an average weight loss of 4.7%, compared with 5.75% for the cattle in the control trailers. Sampling for E. coli O157:H7, Salmonella, and M. haemolytica showed very few positives, likely due to the good condition of the cattle prior to transport. During the 30 days post-transport, no cattle from either treatment required veterinary attention related to transport. The results indicate that increasing ventilation through the use of external air scoops has the potential to improve the health and well-being of cattle during transport.

Half-blood Bonsmara steers were evaluated for temperament during stressful situations to discover the relationships between behavioral stress responses, growth, carcass characteristics and tenderness. Two experiments were conducted to evaluate behavioral stress responses at different stages in the U.S. beef production system with growth, carcass characteristics and tenderness. The first experiment evaluated stress responses at both time of weaning and at the beginning of the feedlot period on half-blood Bonsmara X Beefmaster steers. Steers (n=156) were weaned and paired to destinations of either Uvalde or Overton for winter grazing. At weaning cattle were weighed, and temperament measurements were recorded. After grazing winter pastures, cattle entered the feedlot and were measured for temperament, weight, and condition and frame scores. Cattle were harvested in two groups; each group was selected for harvest when they reached a backfat of approximately 7 mm. Backfat endpoints were determined by visual assessment and ultrasound. Carcass data were recorded approximately 36 hrs post-mortem, and 2.5cm steaks were removed from the 13th rib for Warner-Bratzler shear force determination. The second experiment involved Bonsmara X Angus (n=207) steers grazed on wheat pasture and fed at Cattletown feedlot near Hereford, TX. The steers were evaluated near the beginning and end of the finishing phase for performance and temperament. They were harvested in two groups; each group was selected for harvest when they reached approximately 7 mm of backfat as determined by visual assessment and ultrasound. In experiments 1 and 2, behavioral or temperament measures and hormonal responses were related to each other. It appeared as cattle become acclimated to the production system, temperament measures lose their predictive ability. In Experiment 1, weaning exit velocity appeared to be more related to economically important traits such as ADG (r = -0.26), ribeye area (r = -0.37), and Warner Bratzler shear force (r = 0.27), although beginning feedlot exit velocity was associated with feedlot weights (r = -0.30). In Experiment 2, end feedlot measurements tended to be more associated with feedlot weight (r = -0.20), but there did not seem to be any high relationships with carcass characteristics and tenderness.