Browsing by Author "Thomas, Milton G., committee member"
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Item Open Access Beef cattle maternal and terminal economic selection indices(Colorado State University. Libraries, 2013) Zeng, Xi, author; Enns, Richard Mark, advisor; Thomas, Milton G., committee member; Dalsted, Norman L., committee memberThe breeding objective in most livestock operations is to increase profit ability by improving production efficiency. Animals with different purposes are associated with different production systems. The objective of the study is to develop economic selection indices for females and males in three different production systems: maternal, terminal with self-replacement females, and terminal without self-replacement females, based on production characteristics in the intermountain region of the US. Profit equations were constructed to derive economic values under fixed herd size scenario. The parameters used to calculate the cumulative discounted gene expressions (CDGE) and genetic parameters were estimated from 10,007 individual records and 27,165 pedigree records from the Angus herd at the John E. Rouse Beef Improvement Center of Colorado State University. There were 313 sires with an average generation interval of 3.30 years involved in the study, as well as 2,160 dams with an average generation interval of 5.32 years. Sensitivity tests were performed to test the effect of changing production and economic variables on economic selection indices weights. The impacts on selection index for all systems were small with changing production variable. Also, varying economic variables had small effect on selection index of maternal system with correlations among objectives more than 0.80. However, it affects the selection index of two terminal systems a lot with low (-0.05) or even negative (-0.82) correlation between one and another other. The selection responses with considering the cumulative discounted gene expression and based on six economic selection indices were $259.77, $957.10, $93.901, $361.58, $71.81 and $279.30 per generation for females and male in the three production systems, maternal, terminal with self-replacement heifer and terminal without self-replacement heifer, assuming that the selection intensity is one standard deviation. Under all scenarios, selection will lead to increasing profit.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 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 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 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 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 Selection for fertility in lactating dairy cows: implications of conceptus-derived signals(Colorado State University. Libraries, 2016) Liebig, Bethany Ellen, author; Hansen, Thomas R., advisor; Thomas, Milton G., committee member; Van Campen, Hana, committee member; McConnel, Craig S., committee memberInfertility is a source of major economic loss in the dairy industry. Selection for fertility in dairy cows is difficult because fertility traits based on a genetic evaluation, such as daughter pregnancy rate (DPR), are lowly heritable (h2 ≤ 0.04), influenced by on-farm events, such as services per conception (SPC), and influenced by complex mechanisms that cause embryo mortality (EM). Embryo survival depends on robust interferon tau (IFNT) production and release from the trophectoderm, induction of IFN stimulated genes (ISG) in the endometrium to block the luteolytic, pulsatile release of prostaglandin F2α (PGF), and continued progesterone production by the corpus luteum throughout maternal recognition of pregnancy. Genes negatively affecting IFNT and ISG expression may increase the occurrence of EM. We hypothesized that selection for high direct genomic value for DPR (DGV-DPR) and low on-farm SPC records would be associated with increased: 1) IFNT production by the conceptus, 2) ISG expression in endometrium and peripheral blood mononuclear cells (PBMC), and 3) embryo survival. Freshening dairy cows (n=86) were sorted by DGV-DPR (determined by Clarifide®, Zoetis) and SPC into high fertile (HF; -1.3 DGV-DPR; 1.4 SPC) nonpregnant (NP) or pregnant (HP), and low fertile (LF; -2.3 DGV-DPR; 3.7 SPC) pregnant (LP) groups (n = 7 each). After the voluntary wait period, cows were estrous synchronized and time-artificially inseminated to a HF bull (+1.8 DPR). NP cows were not inseminated. On day 16 following onset of estrus, embryos were flushed from the uterus and typed as viable or EM based on morphology and length. The DGV-DPR was negatively correlated (r = -0.57; P < 0.05) with SPC. Days in milk and number of lactations were not different between groups. Serum progesterone tended (P < 0.10) to be lower in the cows carrying EM embryos than NP cows. Two of 7 embryos from HP cows and 3/6 embryos from LP cows were classified as EM. Viable embryos were significantly (P < 0.05) longer than EM embryos when fertility group was not considered. Viable HP embryos tended to be longer (P < 0.10) than LP embryos. Interferon tau concentrations in uterine flushing (UF) were: 1) greater in HP compared to LP and NP cows (P < 0.05), 2) positively correlated with DPR (r = 0.68; P < 0.05) and 3) negatively correlated with SPC (r = -0.59; P < 0.05). Interferon stimulated gene 15 mRNA concentrations were significantly: 1) upregulated in endometrium from HP viable compared to LP viable and NP cattle (P < 0.05), and 2) upregulated in peripheral blood mononuclear cells from HP compared to LP and NP cows (P < 0.05). Furthermore, ISG15 protein concentrations in endometrial tissue were significantly upregulated in HP compared to LP and NP cattle (P < 0.05). In conclusion, selection of dairy cows combining DPR and SPC may improve fertility through increased production and action of IFNT.Item Open Access The physiological ramifications of chorionic somatomammotropin RNA interference(Colorado State University. Libraries, 2021) Tanner, Amelia R., author; Anthony, Russell V., advisor; Rozance, Paul J., advisor; Engle, Terry E., committee member; Thomas, Milton G., committee member; Winger, Quinton A., committee memberTo view the abstract, please see the full text of the document.