Browsing by Author "Enns, R. Mark, advisor"
Now showing 1 - 15 of 15
Results Per Page
Sort Options
Item Open Access Angus cattle at high altitude: pulmonary arterial pressure, estimated breeding value and genome-wide association study(Colorado State University. Libraries, 2016) Zeng, Xi, author; Thomas, Milton G., advisor; Enns, R. Mark, advisor; Speidel, Scott E., committee member; Holt, Timothy N., committee memberTo view the abstract, please see the full text of the document.Item Open Access Developing a strategy for identifying genetically important animals(Colorado State University. Libraries, 2023) Wilson, Carrie S., author; Speidel, Scott, advisor; Enns, R. Mark, advisor; Lewis, Ronald, committee member; Mason, Esten, committee memberLivestock researchers often need to sample animals within a breed to serve as a representative sample of the breed. Identifying the most relevant animals to include in research for genotyping, building a reference population, or inclusion in a gene bank is a complex issue. A suboptimal sampling strategy can lead to biased results, the need for additional sampling, and can be costly. When using public funds (e.g., federal grant or federal appropriations) or member fees (e.g., breed association funds), we have a responsibility to efficiently spend these investments in a wise manner, optimizing which animals are sampled before the research, genotyping, or gene banking begins. The first objective was to develop a sampling strategy to maximize the genetic diversity captured for the sampled animals. Simulated data is ideal for this type of study as there is no limitation to the testing parameters. The primary benefit of simulation with this research was the opportunity to have known genotypes for every animal in the population. Since genotypes will almost never be available for the entire population in the real world, and identifying animals to genotype may in fact be the purpose of the sampling, pedigree-based sampling methods were chosen. Sampling methods tested included optimal contribution selection (OCS) and the genetic conservation index (GCI). The OCS selects parents based on constraining their co-ancestry rather than minimizing inbreeding. GCI seeks to maximize the number of founders in an animal's pedigree. The sampling strategy developed in Objective 1 was used to identify a subset of 100, 50, and 25 animals from each breed and the genetic diversity captured by each sampling method was assessed using both quantitative and molecular methods. AlphaSimR was used to simulate the population for sampling. After an initial randomly mating founder population was developed, an additional 15 years of selection for phenotypic weaning weight was simulated and resulted in a fully genotyped population with 13,662 animals per year. The simulation was designed to represent a sheep population. After the sampling strategies were applied to the simulated population, they were next applied to Suffolk sheep and Simmental beef populations for further assessment of their ability to capture genetic diversity. To assess population structure based on molecular data, the Suffolk and Simmental populations were limited to genotyped animals and their ancestors. The simulated population represented a large purebred population (n=204,930) with a moderate number of markers (n=53,901). The Suffolk population represented a small population (n=1,565) with many markers (n=606,006). Lastly, the Simmental population represented a large, admixed population (n=54,790) with a moderate number of markers (n=29,449). For the second objective, the population structure of the full populations, comprised of genotyped animals, was assessed, and compared to the population structure of the animals from each sampling strategy. Each sampling strategy selected 100, 50, and 25 animals. The measure of success of capturing the genetic diversity of the population was a molecular-based measure defined by capturing the available alleles in the population. Other population structure measures included a comparison of a phenotypic trait, breeding values, inbreeding levels, heterozygosity, minor allele frequency (MAF) category classification, runs of homozygosity (ROH), Ne, and model-based population structure to visualize subpopulations. While both sampling strategies were effective at capturing the available alleles in the population, OCS was more successful than GCI when comparing the same sample size. Success of capturing alleles decreased as sample size decreased from 100 to 50 to 25. Overall, OCS with a sample of 100 animals (OCS 100) was the most successful at capturing the available alleles in the population, capturing 96.5, 99.3, and 99.9 percent of the alleles for the simulated, Suffolk, and Simmental populations, respectively. For a sampling strategy to be useful, it needs to be effective across a variety of species and breeds with a variety of breed histories and population sizes. The third objective was to compare the three populations evaluated in this research and compare the effectiveness of the sampling strategies across these populations. Population structure was compared for the three populations. Then, the effectiveness of OCS 100 was compared. The three populations differed in population size and the amount of admixture present. The simulated population was characterized by a large number of low frequency alleles (n=5,339) that proved difficult to capture. The Suffolk population was small and consisted of 14 distinct subpopulations. The Simmental population had high levels of heterozygosity and less distinct subpopulation structure. Despite disparate populations, OCS 100 was the most robust across the three populations, consistently capturing the highest percentage of available alleles compared to the other sampling strategies. In summary, OCS 100 was the most effective sampling strategy across three different populations. A low-cost pedigree-based sampling strategy can be used to capture the genetic diversity in a population. Researchers will need to weigh the risk of a greater loss of alleles when selecting a smaller population size. Risk could be further reduced by increasing the selected population size. Knowledge of the prevalence of low frequency alleles in the population and the value of capturing them should be considered.Item Open Access Effects of beef cow milk production levels on longevity and stayability(Colorado State University. Libraries, 2014) Culbertson, Miranda M., author; Enns, R. Mark, advisor; Thomas, Milton G., committee member; Pritchett, James, committee memberThe objective of this study was to determine the effects of beef cow milk potential on their ability to remain in the herd. We hypothesized that in areas with more arid climates and associated forage quantity and quality challenges, cows with higher genetic potential for milk production, measured as milk EPD, may not remain in the herd as long as in more favorable environments. Two sources of data were used to examine this effect. The Red Angus Association of America provided breeder and herd records for stayability on 120,871 cows from 229 breeders with each herd subsequently classified into 8 different environments (biomes). In order to measure length of productive life, a score for longevity was assigned to each cow as the age at which she calved her last calf. Data were analyzed in ASREML3.0 using a mixed model with milk EPD, metabolic weight EPD and biome class as fixed effects to predict cow longevity (length of productive life). The quadratic term of milk EPD2 was included in the model as well as an interaction between milk EPD2 and biome. The interaction term was significant (P<0.001) with regression coefficients of 0.01414, 0.01693, 0.01096, 0.010504, 0.002240, 0.017331, 0.019607 and 0.014834 for the eight biomes of California Division, Subtropical Division, Prairie Division, Eastern Great Plains Division, Western Great Plains Division, Dry Domain, Rocky Mountain Province, and Hot Continental Division, respectively. The positive coefficients indicated that as levels of milk EPD increased so would longevity; however, rates were different depending upon biome. A logistic regression was also performed using SAS 9.3 with stayability to 6 years of age (a binary outcome) as the dependent variable for milk EPD, milk EPD2, metabolic weight EPD and biome as fixed effects. An interaction term for biome with milk EPD, and biome with milk EPD2 was also included and was significant (P<0.0001). As milk EPD increased the probability of a cow remaining in the herd increased for all biomes quantified by odds ratios. The second source of data was provided by the Colorado State University John E. Rouse Beef Improvement Center (BIC). Using SAS 9.3, the regression of longevity on the linear and quadratic effect of cow's milk EPD as a main effect was conducted resulting in a regression coefficient of 0.1002. This positive regression coefficient suggested that for higher levels of milk EPD, the positive relationship between milk EPD and longevity increased. Logistic regressions were also conducted with the BIC data for the binary outcomes of stayability to 3 years of age and 6 years of age with those regressed on milk EPD and milk EPD2. The resulting regression coefficient for stayability of 3 years was -0.0537 with an odds ratio of 0.948. For stayability to 6 years, the resulting regression coefficient was -0.0354 with an odds ratio of 0.965. These results suggested very little change in odds for receiving a stayability score of 1 as milk increases. Based on our results from the data from RAAA, we would reject our hypothesis that in areas of forage restriction that cows with higher milk EPD would not remain in the herd as long as those in environments with more abundant forage. According to the results from the BIC herd, we would also reject our hypothesis that cows with high milk EPD would have an increased probability of being culled from the herd.Item Open Access Estimation of heterotic effects on stayability in beef cattle(Colorado State University. Libraries, 2019) Huff, Emma, author; Enns, R. Mark, advisor; Speidel, Scott, committee member; Holt, Timothy, committee memberStayability in beef cattle is defined as the probability that a cow remains in the herd until age six given that she has calved as a heifer. In some breeds with total herd reporting, those cows are required to calve every year. Stayability influences herd profitability by decreasing the need for replacements by increasing the number of cows that reach the typical breakeven age of six. Stayability is a binary trait on the observed scale and is considered a lowly heritable trait. General consensus is that lowly heritable traits should be subject to higher levels of heterosis in crossbreeding programs. Therefore, heterosis should have a positive effect on the cows' ability to remain in the herd until age six. The objective was to estimate maternal and individual heterosis values for stayability. Data was obtained from the American Gelbvieh Association and included a total of 13,114 animals, with 5 being purebred American Angus and 5,493 purebred Gelbvieh, and the rest being a combination of crossbred animals. Variance components and fixed heterosis effects were estimated from single trait animal models using a probit threshold link function. The model included contemporary group as a fixed effect and breed percentage as a linear covariate. Two models were evaluated with different heterosis covariates, model one included only individual heterosis and model two included individual and maternal heterosis. Heterosis was estimated to be 48.96% when individual heterosis is 100% with the first model. For the second model 100% individual heterosis was estimated to be 48.88% and 49.57% was the estimate for 100% maternal heterosis. The results from this experiment indicate that stayability is affected by heterosis and that these effects should be accounted for in cattle evaluation using pure and crossbred data.Item Open Access Evaluating the genetic relationship between high elevation pulmonary arterial pressure and moderate elevation feedlot performance and carcass traits(Colorado State University. Libraries, 2020) Briggs, Emma, author; Speidel, Scott E., advisor; Enns, R. Mark, advisor; Thomas, Milt G., committee member; Holt, Tim, committee memberThe objective of the study was to evaluate if a genetic relationship exists between post weaning pulmonary arterial pressure (PAP) measured at high elevation and traits associated with moderate elevation feedlot performance and carcass traits. For this study, PAP (collected 1992-2018; n = 6,898), feedlot performance (2014-2018; n = 558), and carcass data (2001-2018; n = 1627) were obtained from the Colorado State University Beef Improvement Center Angus herd. At an elevation of 2,115 m, post weaning, PAP measurements were collected; subsequently, a selected group of steers were relocated to a moderate elevation feedlot (1,500 m) where feedlot performance data was collected. Genetic relationships were evaluated with a series of 5-trait models using REML statistical approaches. Traits in this analysis were assigned contemporary groups, fixed effects and a direct genetic random effect. A maternal additive and permanent environmental effect was included to weaning weight in the analysis. The heritability estimate for PAP was 0.20 ± 0.03. Genetic correlations between PAP and feedlot traits were positive, with estimates of 0.32 ± 0.20 (average dry matter intake) and 0.03 ± 0.17 (average daily gain). The strongest genetic correlation between PAP and carcass performance traits were those of rib eye area (-0.30 ± 0.12) and calculated yield grade (0.29 ± 0.12). Genetic correlations between PAP and marbling score, back fat, or hot carcass weight were 0.00 ± 0.13, -0.07 ± 0.13, and 0.14 ± 0.10, respectfully. These results suggest a favorable genetic relationship exists between PAP and feedlot and carcass traits. As cattle with lower post-weaning PAP move to lower elevation feedlot, they could potently have heavier muscled carcasses compared to their high PAP contemporaries.Item Open Access Feedlot heart disease: understanding heart score and its relationships to economically relevant traits(Colorado State University. Libraries, 2022) Kukor, Isabella, author; Speidel, Scott E., advisor; Enns, R. Mark, advisor; Holt, Timothy N., committee member; Thomas, Milton G., committee memberThe increasing occurrence of feedlot heart disease caused by pulmonary hypertension has precipitated a growing concern from producers and geneticists alike. Utilization of genetic technology for selection and breeding decisions has made a substantial amount of progress in past decades within economically relevant traits, but the focus on high performing cattle may have had adverse consequences on cardiovascular fitness. Pulmonary hypertension has become a more frequent occurrence in low to moderate elevation feedlots, causing feedlot death and the potential to predispose cattle to co-morbidities. Previously, once considered only a high-altitude issue, pulmonary hypertension appears prevalent in high genetic merit cattle within moderate elevation, high plains feedlots. With no options for treatment, management, and prevention in feedlot cattle may be the only strategy for producers struggling with the balance of desirable, fattening cattle and pulmonary hypertension risk. The objective of this study was to establish the foundation for a new heart grading system known as heart score and discover its genetic and phenotypic relationships with economically relevant traits and differentiate phenotypic differences between healthy and unhealthy scored Angus-influenced cattle. The third chapter of this thesis included phenotypic differences between cattle with healthy and unhealthy heart scores (n = 1,422). Data were obtained from Cactus Feed Yard LLC in Canyon, Texas over a two-year period (2020-2022). Means were compared between heart score groups (1,2 & 3+) to test for significant differences between the two groups. Linear models and the ANOVA table displayed significant fixed effects to each model. Systolic, diastolic, PAP, and marbling scores differed among groups (P < 0.05), while hot carcass weight displayed a tendency (P < 0.10). Unhealthy heart scored cattle tended to be heavier carcasses associating heavier cattle with pulmonary hypertension. Healthy heart scored animals had overall lower (P < 0.05 ) PAP, systolic, and diastolic measurements. The fourth chapter of this thesis highlighted the differences between repeated PAP measurements at 9 and 14 months of age. The cohort of Angus influenced cattle were housed at a feedlot in Canyon, TX and was a moderate altitude (1,080 m). Repeated PAP measurements exhibited an increase in PAP measurements between 9 months and 14 months of age, which were later grouped by their heart scores. No differences were observed among heart scored cattle at 9 months (mean minimum: 39.61 ± 2.47; mean maximum: 40.36 ± 3.47) but distinct differences were observed among cattle grouped in their 14-month PAP (mean minimum: 45.27 ± 5.69; mean maximum: 79.20 ± 21.09). High heart scores were associated with higher PAP measurements. There was a correlation of 0.20 between the measurements showcasing a positive trend between measurements, but also the inability of PAP measurements taken at 9 months may not be predictive of cattle's scores at 14-month-old. Furthermore, there were no differences between phenotypic traits of the cattle who had greater PAP differences between their measurements. The third study estimated the heritability of heart score and the phenotypic relationships with economically relevant traits (n = 1,507) in progeny of 88 sires. Phenotypes included heart scores, PAP (14 months), hot carcass weight, marbling, ribeye area, and backfat. Heart score was found to have a moderate heritability estimate 0.28 ± 0.10. Heart score had a very strong genetic correlation with PAP, and strong correlation with hot carcass weight. Positive genetic correlations were found between heart scores and carcass traits with genetic correlations between 0.07 to 0.63. Overall, these results suggest heart scores to be useful in genetic selection for a healthier cardiopulmonary system. while not drastically influencing carcass traits.Item Open Access Genetic parameter estimation and dry matter intake calculation as it applies to feed utilization in beef cattle(Colorado State University. Libraries, 2010) Pendley, Cory T., author; Crews, Denny, advisor; Enns, R. Mark, advisor; Carstens, Gordon E., committee member; Pendell, Dustin, committee memberThe majority of mating systems in the U.S. beef industry have focused on increasing revenue by applying selection pressure to economically relevant traits (ERT) for outputs such as growth, calving ease, and carcass quality. There are other ERTs that affect profitability that can be improved through selection like feed intake, heifer pregnancy, and longevity. The purpose of this thesis was to expand the effective use of residual feed intake (RFI) in two distinct manners. Therefore, the objectives of the first study were to compile published estimates of heritability and genetic correlations of feed conversion ratio (FCR), RFI, average daily gain (ADG), metabolic body weight (MBW) and dry matter intake (DMI). These estimates were used to calculate weighted estimates of the respective genetic parameters. Twenty-five sets of estimates involving more than 40,000 cattle published between 1961 and 2010 were included in a meta-analysis of genetic parameters for feed intake and related traits. A generalized least squares approach was used to compute weighted mean heritability and genetic correlation estimates, as well as their SE, where weights were a function of inverse SE. Weighted heritability estimates for FCR, RFI, ADG, MBW and DMI were 0.28±0.06, 0.38±0.08, 0.32±0.08, 0.39±0.08, and 0.38±0.06, respectively. Weighted genetic correlations of FCR with RFI, ADG, MBW, and DMI were 0.60±0.07, -0.31±0.14, 0.03±0.14, and 0.35±0.11, respectively. Weighted genetic correlations of RFI with ADG, MBW were near zero, but were correlated 0.38±0.11 with DMI. The weighted genetic correlation of ADG with MBW was 0.45±0.13. These weighted heritability and genetic correlation estimates may be more useful in the design of genetic improvement programs than relying on estimates from individual studies with low numbers of feed intake observations. For the second study, daily feed intakes were recorded on 3,702 bulls and 314 heifers across nine tests between 2007 and 2010 at Midland Bull Test in Columbus, Montana. Daily feed intake was recorded and from this DMI was calculated. Genetic variances were estimated using a multiple trait animal model and average information REML. The model was equivalent for DMI, ADG, MBW and RFI which included a fixed effect of contemporary group (breed x test x pen, n=112) and a linear covariate for age at start of test (=298.28d, SD=36.65). The heritability estimate for RFIp was 0.17 ± 0.05. Genetic correlations among growth traits (ADG, MBW and DMI) were moderate to high and positive, ranging from 0.33 to 0.70. The model including DMI and RFIp failed to converge. This resulted in the need for estimation of genetic residual feed intake (RFIg), defined as the difference between DMI EBV and expected DMI EBV. Genetic regression was used to predict expected DMI EBV from the EBVs of ADG and MBW. This approach to the genetic evaluation of RFIg allows for the estimation of breeding values that may truly reflect feed utilization differences among animals without simultaneously affecting growth or body size.Item Open Access Genetic parameters for fertility and production traits in Red Angus cattle(Colorado State University. Libraries, 2017) Boldt, Ryan John, author; Enns, R. Mark, advisor; Speidel, Scott E., advisor; Koontz, Stephen, committee memberTo view the abstract, please see the full text of the document.Item Open Access Genetic relationship between ewe longevity and structural foot and leg traits in sheep(Colorado State University. Libraries, 2022) Yazar Gunes, Hilal, author; Enns, R. Mark, advisor; Speidel, Scott E., advisor; Thomas, Milton G., committee member; Holt, Timothy, committee memberTo view the abstract, please see the full text of the document.Item Open Access Heifer pregnancy genetic prediction and simulation modeling techniques(Colorado State University. Libraries, 2008) Comstock, Carlton R., author; Enns, R. Mark, advisor; Bourdon, Richard M., advisorThe Colorado Beef Cattle Production Model (CBCPM) was rewritten with an object oriented design and used to simulate heifer pregnancy data with varying levels of age at puberty (AAP), probability of conception (PCON), and length of breeding season. Five percent of the heifers were simulated infertile due to non-genetic causes. Simulated data were used to estimate heritability of heifer pregnancy and to obtain EBV using threshold models. The EBV were tested for accuracy of prediction of the simulated genetic fertility traits. Object oriented methods used illustrated the ability of these techniques and tools, such as Unified Modeling Language, at organizing complex processes in ways to reduce errors and code maintenance effort, and to facilitate collaboration among developers. Adoption of these tools will be critical to the advancement of systems models. Heritability of heifer pregnancy from 20,000 heifers with very early puberty in the first 25 d of the breeding season was .139, .107, and .143 for mean PCON of 60, 70, and 80%, respectively, close to the .10 input heritability of PCON. The higher estimates may be due to a few heifers having two opportunities to breed. With very late puberty and 80% mean PCON in a 25 d breeding season the heritability estimate of AAP was .337, lower than the simulated .40 heritability. The estimate was lower because there was not 100% conception, some heifers were infertile, and puberty was observed as a threshold trait. Heritability estimates of heifer pregnancy generally decreased as breeding season length increased, likely due to an increasing percent of open infertile heifers. The ability of the variance component estimation software to converge on an estimate decreased as the number of open, fertile heifers decreased. The most difficulty was with high PCON, early puberty, and long breeding seasons; only one out of 100 estimates converged at 340 d AAP, 80% PCON, and 120 d breeding season. Calculated accuracy for heifer pregnancy EBV for the sires of the heifers using prediction error variances from a linear model, with the binary pregnancy observations treated as continuous data, overestimated accuracy of the EBV with respect to the simulated traits in all cases. Calculated accuracy was insensitive to changes in frequency of heifer pregnancy observations. Accuracy calculated as the simple correlation of the EBV with each simulated fertility trait for the sires of the heifers was highest in most cases at the shortest breeding season. The correlation with AAP was essentially zero for early puberty, and strongest (-.775) at late puberty. As breeding season length increased the AAP correlation declined toward zero. The accuracy for PCON was less sensitive to changes in AAP and breeding season length, ranging from .146 to .753; the strongest correlations were with early puberty and low PCON.Item Open Access Heritability and repeatability estimates of first service conception and first cycle calving in Angus cattle(Colorado State University. Libraries, 2019) Foxworthy, Heather, author; Enns, R. Mark, advisor; Speidel, Scott E., advisor; Thomas, Milton G., committee member; Callan, Robert, committee memberDescribed as the ability of an individual to conceive and remain pregnant, fertility remains one of the largest economic impacts on cattle producers. Infertility and(or) sub-fertility in the cow herd can result in financial losses due to a reduction in calf crop, lower quality calves, and increased breeding and replacement costs. Improving reproductive efficiency via altered management and selection could prove useful for cattle managers to minimize these costs while increasing genetic gain and income. However, historically the investigation of fertility traits has been minimal due to the binary nature of many of the traits making analysis difficult. In addition, given the nature of the phenotypes, heritability estimates of fertility traits are generally low, suggesting minimal genetic influence and therefore slow rates of genetic gain. First service conception (FSC) is a binary trait that describes the outcome of the first service of artificial insemination (AI) with success or failure phenotypes. Furthermore, a trait termed first cycle calving (FCC) describes the ability of a female to calve within a 21-day period of the due date based on the initial opportunity for conception in the first 21 days of the breeding season. The objectives of this thesis included the further investigation of the influential factors, genetic and environmental, on the success of first service conception and first cycle calving with the end result estimates of heritability and repeatability for these traits in Angus cattle. Data used for this analysis was sourced from the Colorado State University Beef Improvement Center (1985 to 2018; CSU-BIC; N = 8,206) near Saratoga, Wyoming where an Angus cow herd is managed for research purposes. The data used included breeding and ultrasound records, as well as data on the resulting and previous calves. Model selection resulted in fixed effects of birth year (P < 0.001), mating type (insemination based on estrus or during mass mating; P < 0.001), contemporary group consisting of synchronization protocol, semen type, and mating year (P < 0.001), previous calving ease (P < 0.001), and covariates of mating age in days (P < 0.01), and post-partum interval (P < 0.001) for both FSC and FCC. Variance components for the two traits were estimated using a REML procedure and then combined into estimates of heritability and repeatability. Analysis resulted in estimates of 0.03 ± 0.02 and 0.15 ± 0.03 for FSC and FCC, respectively for both heritability and repeatability when considering the entire female reproductive lifespan. When observations were segregated into immature and mature categories of beef females one to four years of age at mating and five years or greater, differences in parameter estimates became apparent. Estimates of heritability for FSC in immature and mature females were 0.04 ± 0.04 and 0.02 ± 0.05, respectively while repeatability was estimated for the two categories at 0.04 ± 0.04 and 0.08 ± 0.04. These estimates for mature females suggested a detectable influence of the permanent environment; however, all estimates are considered low for their respective parameter. When estimating the parameters for FCC, heritability was estimated at 0.04 ± 0.07 and 0.21 ± 0.04 for immature and mature female categories, respectively; while repeatability values were 0.11 ± 0.07 and 0.21 ± 0.04, respectively. These estimates suggest a permanent environmental effect; however, estimates of both parameters for immature females were low, while those for mature females can be classified as moderate. The findings suggested that altering temporary environmental management should remain the most critical factor when improving female reproduction. The largest genetic contribution was for FCC in mature females resulting in more potential for selection and culling based on the phenotype for that trait.Item Open Access Heterosis and breed percentage effects on reproductive performance and preweaning traits in a multibreed beef cattle herd in Panama(Colorado State University. Libraries, 2023) Gonzalez Murray, Roderick Alexander, author; Speidel, Scott E., advisor; Enns, R. Mark, advisor; Thomas, Milton G., committee member; Coleman, Stephen J., committee member; Holt, Timothy, committee memberPanama is located in Central America and is characterized by a tropical climate. Given the tropical climate conditions, Zebu cattle (Bos indicus) are the most predominant breeds in cow–calf systems due to greater resistance to internal and external parasites, and greater tolerance to elevated ambient temperatures and humidity when compared to Bos taurus beef breeds. Zebu is a breed that is reproductively inefficient due to Age at First Calving (AFC) being over 36 months and having longer calving intervals (CI), ranging between 12.2 to 26.6 months. The Panamanian cow-calf system reports an average annual birth rate of 55%, with a range of 35% to 60%, depending on the province. This reduced efficiency reported in the cattle production system is also reflected in low kilograms of weaned calves per cow exposed to AI or Bull (80kg) to 120 WW/cow exposed), high age at first calving (over 36 months), long calving interval (more than 450 days), and perhaps low-income returns ranging between 8 to 15% per dollar invested. The reproductive efficiency of a herd is one of the main components of a cow-calf system economically. Other important traits that affect the system efficiency and profitability are the preweaning traits: birth weight (BW) and weaning weight (WW). The lack of system efficiency and profitability is why different breeds have been introduced to the country to be used in crossbreeding systems to obtain the benefits of heterosis in growth and reproductive traits. The beneficial effects of crossbreeding on animal performance have been well established, benefiting low heritability traits such as those related to reproduction. For that reason, in tropical environments, matching the optimum cow numbers with the correct genetic potential in the appropriate production environment can maximize economic benefits. In the tropics, reduced pre- and post-weaning growth and reproductive efficiency are the main limiting factors in the cow-calf system. Preweaning traits are a combination of the direct genetic, maternal genetic, maternal permanent environment, and temporary environmental effects. The challenge for farmers in Latin American countries is to identify those animals that achieve maximum productive performance in a given agro-ecological environment, and to maintain a balance between longevity and generation intervals, in order to obtain the greatest genetic gain per unit of time. Knowledge of the genetic effects of breeds and their crosses in various climatic and forage conditions can be used to identify optimal breed combinations and crossbreeding systems for existing markets. Based on the heterogeneity of herds in tropical regions due to the introduction of multiple breeds and the different crossbreeding systems utilized, it is necessary to carry out a multibreed evaluation that includes all crossbred and purebred individuals into a single analysis and accounting for the direct and maternal breed and heterosis effect evaluation. As we mentioned above, different breeds have been introduced in Panamá, but no genetic evaluation program has been developed in the country, to improve the efficiency of cow-calf production. However, it is important to evaluate the breed groups and heterosis effect through productivity indicators to know the relative performance of the breeds and crosses of Zebu and Bos taurus cattle in the cow–calf system. Therefore, the objectives of this study were to determine heterosis and breed percentage effects on reproductive performance and preweaning traits in a multibreed beef cattle herd in Panama. For this, traits like age at first calving (AFC), calving interval (CI), gestation length (GL), birth weight (BW), and weaning weight (WW) that constitute important elements of the breeding objective of beef cattle producers were selected as the traits to evaluate in this study. All the reproductive and preweaning data utilized in this investigation was produced by a multibreed cattle population of the Livestock Experimental Station of Panama Agricultural Innovation Institute (IDIAP) in Gualaca, province of Chiriqui, Republic of Panama. The herd was comprised of the following genetic groups and breed percentage combinations: tropical adapted Brahman (BR), Nellore (Ne), Undefine Bos indicus (BI), Guaymi Creole (CR), Senepol (SP) Romosinuano (RS); Bos taurus (BT), Simmental (SM), Angus (AN), Red Angus (AR), Limousin (LM), Charolais (CH), Wagyu (WA), and Others (OTH); crossbreeds (CX), Beefmaster (BF), Three CX (F1 x different BT), R1(Backcross BR), R2 (Backcross BT), Composite (combination of at least 4 different breeds with less than 25% of Zebu), Upgraded Brahman (87.5% BR 12.5% BT), B1 (62.5% Zebu + 37.5% BT), B2 (62.5% BT + 37.5% Zebu). In general, this dissertation was divided into three different studies according to the physiological status of the individual producing the phenotypic record (e.g., calf, heifer, and multiparous cows). The first study estimated the influence of heterosis and breed percentage on age at first calving (AFC). An animal model was utilized to estimate variance components using data from 619 cows and 1,142 individuals in the pedigree from the multibreed herd with data collected between 2000 to 2019. The average AFC was 42.7 ± 10.5 months, with an estimated regression coefficient for AFC on heterosis of -0.046 ± 0.009 month/percent of outcross. Lower AFC was observed for the F1, R2, and B2, with 39.8 months, 39.9 months, and 39.5 months, respectively. A reduction in AFC was also observed for the Beefmaster (-0.13 ± 0.05 months) and the OTHER category (-0.14 ± 0.04 months). A heritability of 0.17  0.10 was estimated for AFC. These results suggest that heterosis had a beneficial influence on AFC measurements in a multibreed beef cattle herd in Panama. The second study focused on estimating the influence of heterosis and breed percentage on calving interval (CI) and gestation length (GL), and the correlation between age at first calving (AFC) and CI. Calving performance data included 1,291 repeated observations of CI and GL from 502 cows with a 3-generation pedigree consisting of 2,840 individuals in the pedigree with data collected between 2000 to 2021. A repeated records animal model was utilized to estimate variance components for both CI and GL. Additionally, a bivariate animal model was used to estimate the genetic correlation between CI and AFC. The average CI was 572.6 ± 140 days, and for GL was 284.2 ± 6.3 days, for this population. The regression of CI and GL on heterosis was not significant. A lower CI was observed for the F1, and Three CX, translating to 558.7 days and 567.2 days, which represents 2.3% and 1.3% reduction in CI, respectively when compared to the Zebu group. Calving interval was estimated to be lowly heritable (0.037 ± 0.026), however, a positive genetic trend over the duration of the study. The analysis between CI and AFC revealed a moderate genetic correlation (0.49 ± 0.36) which allows the establishment of a selection program to improve AFC and CI, due to the pleiotropic effect, which would improve the fertility of this multibreed herd in Panama. Finally, the third study aimed to estimate the influence of heterosis and breed percentage on birth weight (BW) and weaning weight (WW). Data from 900 calves with 2,843 individuals in the pedigree was utilized in a bivariate animal model for BW and WW was utilized to estimate variance components. The estimated regression coefficient for BW on heterosis was not significant, however, for WW was 0.072 ± 0.027 kg/percent of outcross. Lower BW and WW were observed for the Japanese, and B1, while R2 and Upgrade had the highest average WW. Heritability for BW was found to be low 0.14 ± 0.06 and moderate for WW 0.26 ± 0.09. The proportion of variation of WW accounted by the maternal permanent environment for WW was 0.2 ± 0.09. The estimated genetic correlation between additive genetic BW and WW was 0.63 ± 0.30, while a negative, additive genetic correlation was observed for WW and WW maternal -0.43 ± 0.37. These results suggested that heterosis had a beneficial influence on WW but a limited effect on BW. Additionally, increasing the percentage of WA and BR negatively influenced WW measurements in this multibreed population.Item Open Access Pulmonary arterial pressure as an indicator for high altitude disease in cattle: breed differences and relationships with growth performance(Colorado State University. Libraries, 2015) Crawford, Natalie Faye, author; Enns, R. Mark, advisor; Thomas, Milton, advisor; Holt, Timothy, committee memberHigh altitude disease (HAD), commonly known as brisket disease, is a natural occurring phenomenon in cattle. This disease occurs most often in high altitude (> 1,500 m) environments, where adaptability to the hypoxic conditions may be insufficient. Pulmonary arterial pressure (PAP) scores are the most useful tool available to cattle producers in predicting an animal’s susceptibility to HAD. The all-encompassing objectives for this thesis were to delineate the important factors influencing PAP scores and understand the relationships between PAP scores and other performance traits, where selection for more favorable PAP may have adverse effects on those performance traits. Two sources of data were used for this thesis: Historical records from the San Juan Basin Research Center, 4-Corners Bull Test (1983 to 2005; n = 2,041) and from the Colorado State University Beef Improvement Center (1993 to 2014; CSU-BIC; n = 8,718). For the 4-Corners study, data of yearling age and breed of cattle were used to determine how PAP varies with regards to both of these effects. The model of birth year, pen, breed, and yearling age effects on yearling PAP revealed these terms were all significant predictors of PAP (P < 0.01). With every one-day increase in yearling age, PAP increased by 0.03 (± 0.01) mm Hg (P < 0.01) with a mean PAP of 45.2 ± 12.8 mm Hg. Breed was found to be a highly significant factor (P < 0.001) in the model influencing PAP scores for bulls developed at high altitude. There was a 13.8-mm Hg range between breeds with the lowest adjusted PAP estimate to those with the highest adjusted PAP. The results suggested that appropriate breed selection based on reduced PAP scores could be advantageous in reducing the susceptibility of cattle to HAD and subsequent death due to pulmonary hypertension and right heart failure. The CSU-BIC data contained production weight traits of birth (36.2 ± 5.1), weaning (213.5 ± 31.8), yearling (345.6 ± 83.9), and post-weaning gain (121.9 ± 63.7) and PAP (42.4 ± 9.9) scores and these data were used to estimate heritabilities and relationships amongst them (mean ± SD; kg). Single-trait, two-trait, and multi-trait models revealed genetic correlations between PAP and the weight traits ranging from -0.11 ± 0.10 to 0.23 ± 0.08. An advantage to using a multi-trait model over a two-trait model is the increase in heritability due to the increase of information from more traits evaluated. Results of this study suggested that selection for lower PAP should not have adverse effects on the growth performance traits evaluated.Item Open Access Pulmonary arterial pressure in Angus cattle: environmental influences and relationship with growth and carcass traits(Colorado State University. Libraries, 2017) Pauling, Rachel, author; Enns, R. Mark, advisor; Holt, Timothy N., committee member; Speidel, Scott E., committee member; Thomas, Milton G., committee memberRight-side heart failure (RHF) resulting from hypoxia induced pulmonary hypertension is most commonly observed in cattle located at high elevations, but has been observed in some feedlot cattle residing at low elevations as well. Beef cattle producers typically use pulmonary arterial pressure (PAP) observations to predict an animal's susceptibility to RHF. The objective of this this study was to investigate the effect of elevation on PAP measures, and to evaluate the relationship between PAP, growth traits, and carcass traits in Angus cattle. The first study utilized PAP and elevation data obtained from the American Angus Association (AAA, n = 4,511), Colorado State University Beef Improvement Center (n = 5,433), and Dr. Timothy Holt DVM (n = 4,821). A univariate analysis of PAP as used to obtain elevation solutions to be input to a polynomial regression to determine high versus low elevation (1,620 m). Then a bi-variate analysis was performed to evaluate the genetic relationship between PAP observations obtained at high elevations as well as low elevations. Results from this study indicate that PAP observations obtained at any elevation can be considered the same trait with a genetic correlation of (0.83 ± 0.15). The second study utilized data obtained from AAA (n = 4,509) which included PAP, growth, and carcass traits. Multivariate analyses of PAP and growth traits, as well as PAP and carcass ultrasound traits were used to obtain estimates of heritability and genetic correlations. Results from these analyses indicated that there are moderate genetic correlations between PAP and maternal birth weight (0.55 ± 0.12) as well as PAP and ultrasound ribeye area (0.24 ± 0.12). These results suggested that selection for increased growth and muscling in cattle could consequently increase PAP observations.Item Open Access Random regression models for the prediction of days to finish in beef cattle(Colorado State University. Libraries, 2011) Speidel, Scott Eugene, author; Enns, R. Mark, advisor; Crews, Denny, committee member; Peel, R. Kraig, committee member; Hess, Ann, committee memberTo view the abstract, please see the full text of the document.