Thesis (M. Sc.)(Animal Science)--University of Pretoria, 2005. / Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (M.S.)--Virginia Polytechnic Institute, 1946. / Includes bibliographical references (leaves 152-158). Also available via the Internet.

The objectives of this study were accomplished with two experiments in growing Bonsmara bulls (N = 68) (experiment 1), and Simmental crossbred calves (N = 132) (experiment 2). Specific objectives for experiment 1 were to characterize residual feed intake (RFI) in growing bulls, and examine relationships between RFI and performance, fertility, temperament and body composition traits. In experiment 2, the objectives were to examine stocker-phase supplementation effects on feedlot feed conversion ratio (FCR) and RFI and to characterize relationships between these feed efficiency traits, and performance and carcass traits in finishing calves. In both experiments, individual feed intakes and BW were measured. Ultrasound technology was used to measure body composition in experiment 1, while actual carcass measurements taken at harvest were used for experiment 2. Experiment 1 demonstrated that temperament affected ADG and DMI, but not FCR or RFI. Residual feed intake was not phenotypically correlated to scrotal circumference or bull fertility traits. Experiments 1 and 2 demonstrated that RFI was independent of ADG and BW, but that there was a tendency (P < 0.10) for RFI to be phenotypically correlated with 12th rib fat thickness (r = 0.20 and 0.22). However, RFI was not correlated with longissimus muscle area in either experiment. Both experiments demonstrated that low RFI (< 0.5 SD below mean RFI) calves consumed significantly (20 and 22%) less feed and had improved (21%) FCR compared to calves with high RFI (> 0.5 SD above mean RFI). Results from experiment 2 suggest that RFI measured while calves are consuming high-grain diets may be less influenced by previous level of stocker supplementation compared to FCR or residual gain efficiency traits. In summary, RFI was found to be phenotypically independent of growth rate and BW, had no effect on bull fertility or temperament traits, and was less impacted by previous plane of nutrition compared to FCR.

The implementation of the Central America-Dominican Republic Free Trade Agreement (CAFTA-DR) has expanded trade opportunities for U.S. agricultural producers. U.S. beef is a critical product affected by the legislation, and the United States Meat Export Federation (USMEF) invested in a new product promotion program to increase exports of U.S. beef to Guatemala. The consumer responsiveness and effectiveness of the U.S. branded beef promotion program are analyzed in this study. Demand responses to promotion activities that launched three new U.S. beef value cuts in Guatemala’s Hotel, Restaurant and Institutional (HRI) sector were estimated by applying the Parks Model of Generalized Least Squares regression to pooled, time-series and cross sectional data. Results show a negative relationship between own price and sales quantity, while the effect of advertising on quantity sold is positive. Demand for the U.S. beef value cuts increased as a result of the promotion, although the costs of the promotion program exceeded the additional revenue generated as a result of promotion activities.

The objective of this study was to update the existing nutritional data available in the USDA National Nutrient Database for Standard Reference by providing revised nutritional information on the round and loin cuts evaluated in Phase III of the Nutrient Database Improvement Project. A total of 20 carcasses were selected from three packing plants across the United States, and round and loin subprimals from these carcasses were collected and transported to Texas A&M University. These subprimals were fabricated 14 to 21 d postmortem, dissected either raw or cooked, and divided to determine the amount of separable lean, separable fat, and refuse amounts per cut. Separable lean from these cuts was homogenized and proximate analyses were conducted in order to determine percent total chemical fat, protein, moisture, and ash. Cooking yields and fat retention values were determined for the cuts that were grilled and roasted. Cuts with external fat had higher cooking yields than cuts with external fat removed. Cuts with external fat had higher fat retention values than the cuts with no external fat. Dissection data indicated that cuts trimmed to lower levels of external fat had the highest values for percent lean and the lowest values for percent seam and external fat and bone-in cuts had the lowest values for percent lean and the highest values for percent refuse. Proximate analyses indicated a decrease in percent moisture as the percentage of total chemical fat increased. Also, round cuts evaluated in the study contained a lower percentage of total chemical fat than loin cuts on a raw basis. When total chemical fat was stratified by USDA quality grade, it was evident that there was a clear separation between upper Choice, lower Choice, and Select cuts. Data resulting from this study will be used to update the existing nutritional database and will provide a current nutritional profile for beef loin and round products.

Neurotensin (NTS) is a tridecapeptide which is widely distributed in the central nervous system and digestive tract. It is highly expressed in neurons of the hypothalamus, a region of the brain known to control feeding behavior. Several studies have shown that intracerebroventricular injection of NTS decreased food intake in rats. NTS was therefore characterized and analyzed for associations with growth and carcass traits in beef cattle.<p>NTS mRNA was successfully isolated from brain, spinal cord, abomasum, rumen wall, small intestine and skin samples. The complete bovine mRNA sequence was obtained from skin, along with partial genomic sequence. Three single nucleotide polymorphisms (SNPs) in the 3 untranslated region (3UTR) and six intronic SNPs were identified. The three SNPs in the 3UTR were not in linkage disequilibrium. Of the three SNPs in the 3UTR, two had minor allele frequencies of 2% and therefore were not analyzed further. The minor allele frequencies for the third SNP (*419G>A) ranged between 0% and 23% for four major beef breeds. The *419G>A SNP was also used to map NTS to bovine chromosome five between markers BM6026 (13 cM, LOD=4.03) and RM103 (4 cM, LOD=3.63).<p>No significant associations between the *419G>A SNP and growth traits were identified. Statistical analysis revealed significant genotype associations for rib eye area (REA), grade fat and moisture in the Canadian Beef Reference Herd (CBRH). These associations were not verified in a second group of purebred yearling bulls. However, significant associations with end of trial fat, %fat and fat deviation were associations for marbling and quality grade. In all cases the AA genotype was associated with increased fat.<p>Although significant associations between carcass measurements and genotype at the *419G>A SNP were present in some populations, none of these associations were found in more than one population. It was therefore concluded that the *419G>A SNP on the bovine NTS gene does not prove to have an economic advantage to the beef cattle industry.

Temperament in cattle, defined as an animals response to handling by humans, had been associated with production traits such as average daily gain and meat quality, and can also be considered a welfare issue. Temperament is a stress response trait, and therefore the hypothalamic-pituitary adrenal (HPA) axis likely plays a role in determining individual animals responses. The purpose of this study was to examine whether there are associations between single nucleotide polymorphisms in two genes involved in both the HPA axis and growth, Corticotropin-releasing hormone (CRH) and Leptin (LEP), and various measurements of temperament in beef cattle. In this study, 400 crossbred beef steers were evaluated over three sessions using a traditional subjective score and three objective measurements of response to handling: Strain Gauge (absolute strain force, ASF), Movement Measurement Device and Exit Time (ET) as well as habituation for all measurements (session 3 values session 1 values). Backgrounding growth and final carcass data were also collected. The steers were genotyped at three previously reported SNPs: CRH 22C>G, CRH 240C>G and LEP 73C>T by PCR-RFLP. Subsequently, the genotypes and two-way interactions between LEP and each CRH SNP were analyzed as effects on the various temperament, growth and carcass measurements. There was a significant interaction between LEP and CRH 240C>G for ASF 1, ET 3 and ET 3-1, with the LEP CC/CRH 240C>G CC genotype appearing favorable. Additionally, the LEP CC/CRH 22C>G GG genotype appears to be favorable for ASF 1. These results indicate that it may be possible for cattle producers to select for favorable temperament using these SNPs, however these results should first be validated in additional populations.

This study evaluated methods for controlling Escherichia coli O157:H7 and Salmonella non-pathogenic bacterial surrogates during the production of marinated non-intact beef products. Hot (~30 degrees C) boneless, beef strip loins (n = 54, Institutional Meat Purchase Specification 180) were inoculated with one of two levels (approximately 5.8 and 1.9 log10 CFU/cm2, hereafter referred to as high- and low-inoculated, respectively) of non-pathogenic, rifampicin-resistant E. coli organisms used to simulate harvest floor contamination. The inoculated beef strip loins were chilled at 2 degrees C for 24 h, and then vacuum packaged and aged for 7 to 24 days at 2 degrees C. The beef strip loins were subjected to one of five treatments or control (no treatment). Spray treatments were: 2.5% L-lactic acid, 5.0% L-lactic acid, 1,050 ppm acidified sodium chlorite, 205 ppm peroxyacetic acid, and tap water. Lactic acid treatments were applied at ~53 degrees C, whereas the other sprays were applied at room temperature (~25 degrees C). Treated and control pieces were tumble marinated using a commercial marinade. Sample counts were collected throughout the experiment to track reductions in inoculated microorganisms as impacted by antimicrobial treatment and processing. For the high-inoculated strip loins, the 5.0% L-lactic acid treatment was most effective (P < 0.05) across treatments and control at reducing surrogate organisms on meat surfaces before marination, producing a 2.6 log10 CFU/cm2 reduction. The water treatment accounted for the least (P < 0.05) reductions across treatments and control of surrogate organisms on the meat surface before marination. Peroxyacetic acid produced the greatest reduction of surface surrogate organisms in the finished, marinated product. The water treatment resulted in greater internalization of surrogate microorganisms when compared to the control. Furthermore, certain less effective antimicrobial sprays such as water may facilitate internalization of surface bacteria, more so than non-treated subprimals. It is important that producers of non-intact beef products focus on using effective antimicrobial sprays that maximize reductions and minimize internalization of surface bacteria into the finished product.

Neurotensin (NTS) is a tridecapeptide which is widely distributed in the central nervous system and digestive tract. It is highly expressed in neurons of the hypothalamus, a region of the brain known to control feeding behavior. Several studies have shown that intracerebroventricular injection of NTS decreased food intake in rats. NTS was therefore characterized and analyzed for associations with growth and carcass traits in beef cattle.<p>NTS mRNA was successfully isolated from brain, spinal cord, abomasum, rumen wall, small intestine and skin samples. The complete bovine mRNA sequence was obtained from skin, along with partial genomic sequence. Three single nucleotide polymorphisms (SNPs) in the 3 untranslated region (3UTR) and six intronic SNPs were identified. The three SNPs in the 3UTR were not in linkage disequilibrium. Of the three SNPs in the 3UTR, two had minor allele frequencies of 2% and therefore were not analyzed further. The minor allele frequencies for the third SNP (*419G>A) ranged between 0% and 23% for four major beef breeds. The *419G>A SNP was also used to map NTS to bovine chromosome five between markers BM6026 (13 cM, LOD=4.03) and RM103 (4 cM, LOD=3.63).<p>No significant associations between the *419G>A SNP and growth traits were identified. Statistical analysis revealed significant genotype associations for rib eye area (REA), grade fat and moisture in the Canadian Beef Reference Herd (CBRH). These associations were not verified in a second group of purebred yearling bulls. However, significant associations with end of trial fat, %fat and fat deviation were associations for marbling and quality grade. In all cases the AA genotype was associated with increased fat.<p>Although significant associations between carcass measurements and genotype at the *419G>A SNP were present in some populations, none of these associations were found in more than one population. It was therefore concluded that the *419G>A SNP on the bovine NTS gene does not prove to have an economic advantage to the beef cattle industry.

Temperament in cattle, defined as an animals response to handling by humans, had been associated with production traits such as average daily gain and meat quality, and can also be considered a welfare issue. Temperament is a stress response trait, and therefore the hypothalamic-pituitary adrenal (HPA) axis likely plays a role in determining individual animals responses. The purpose of this study was to examine whether there are associations between single nucleotide polymorphisms in two genes involved in both the HPA axis and growth, Corticotropin-releasing hormone (CRH) and Leptin (LEP), and various measurements of temperament in beef cattle. In this study, 400 crossbred beef steers were evaluated over three sessions using a traditional subjective score and three objective measurements of response to handling: Strain Gauge (absolute strain force, ASF), Movement Measurement Device and Exit Time (ET) as well as habituation for all measurements (session 3 values session 1 values). Backgrounding growth and final carcass data were also collected. The steers were genotyped at three previously reported SNPs: CRH 22C>G, CRH 240C>G and LEP 73C>T by PCR-RFLP. Subsequently, the genotypes and two-way interactions between LEP and each CRH SNP were analyzed as effects on the various temperament, growth and carcass measurements. There was a significant interaction between LEP and CRH 240C>G for ASF 1, ET 3 and ET 3-1, with the LEP CC/CRH 240C>G CC genotype appearing favorable. Additionally, the LEP CC/CRH 22C>G GG genotype appears to be favorable for ASF 1. These results indicate that it may be possible for cattle producers to select for favorable temperament using these SNPs, however these results should first be validated in additional populations.