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This thesis summarizes an investigation of antimicrobial resistance (AMR) and antimicrobial use (AMU) in cow-calf herds. The specific objectives of this project were to describe common reasons for treatment and the types of antimicrobials used in cow-calf herds, to describe the frequency of AMR in generic fecal Escherichia coli isolated from various age groups commonly found on cow-calf farms, to determine risk factors associated with the occurrence of AMR, and finally to investigate the underlying molecular mechanisms of AMR in cow-calf herds. At least 86% of the herds treated one or more calves or cows during the study period; however, the overall proportion of both calves and cows reported as treated was less than 14% for calves and 3% for cows. The majority of antimicrobials reported as used in cow-calf operations were for individual therapeutic use rather than prophylaxis, metaphylaxis, or growth promotion. Injectable formulations were the most commonly reported method of antimicrobial administration on cow-calf farms. Cow-calf herds in Wetern Canada are not a significant reservoir for resistance to antimicrobials classified as very important to human medicine such as ciprofloxacin and ceftiofur. The three most common resistances detected were to tetracycline, sulphamethoxazole, and streptomycin regardless of age group. Young calves sampled in the spring of the year were more likely to be shedding AMR E. coli than older calves sampled in the fall of the year or than cows sampled in the spring of the year. The cow-calf pair relationship was not an important factor in transfer of AMR from the individual cow to her calf, but the presence of AMR in the general cow herd was associated with AMR in the calf population. The potential importance of co-selection for AMR at the molecular level was demonstrated by both the risk factor analysis and the molecular work. Phenotypic resistance to streptomycin, tetracycline, and sulphamethoxazole were each associated with the presence of resistance genes from all six families of antimicrobials examined in this study. Several statistically significant associations were also detected between the resistance genes considered. No significant associations were detected between any of the AMR phenotypes or genotypes and the STEC virulence factors stx1, stx2 and eae.

This thesis summarizes an investigation of antimicrobial resistance (AMR) and antimicrobial use (AMU) in cow-calf herds. The specific objectives of this project were to describe common reasons for treatment and the types of antimicrobials used in cow-calf herds, to describe the frequency of AMR in generic fecal Escherichia coli isolated from various age groups commonly found on cow-calf farms, to determine risk factors associated with the occurrence of AMR, and finally to investigate the underlying molecular mechanisms of AMR in cow-calf herds. At least 86% of the herds treated one or more calves or cows during the study period; however, the overall proportion of both calves and cows reported as treated was less than 14% for calves and 3% for cows. The majority of antimicrobials reported as used in cow-calf operations were for individual therapeutic use rather than prophylaxis, metaphylaxis, or growth promotion. Injectable formulations were the most commonly reported method of antimicrobial administration on cow-calf farms. Cow-calf herds in Wetern Canada are not a significant reservoir for resistance to antimicrobials classified as very important to human medicine such as ciprofloxacin and ceftiofur. The three most common resistances detected were to tetracycline, sulphamethoxazole, and streptomycin regardless of age group. Young calves sampled in the spring of the year were more likely to be shedding AMR E. coli than older calves sampled in the fall of the year or than cows sampled in the spring of the year. The cow-calf pair relationship was not an important factor in transfer of AMR from the individual cow to her calf, but the presence of AMR in the general cow herd was associated with AMR in the calf population. The potential importance of co-selection for AMR at the molecular level was demonstrated by both the risk factor analysis and the molecular work. Phenotypic resistance to streptomycin, tetracycline, and sulphamethoxazole were each associated with the presence of resistance genes from all six families of antimicrobials examined in this study. Several statistically significant associations were also detected between the resistance genes considered. No significant associations were detected between any of the AMR phenotypes or genotypes and the STEC virulence factors stx1, stx2 and eae.

Cow-calf producers in western Canada are faced with many decisions throughout the production cycle. The choice of calving time impacts production rate, marketability of calves, income and expenses and net revenue. The purpose of this study was to determine whether June calving could increase net revenues and be a preferred choice across different risk aversion levels over March calving in western Canada. Data for this study were taken from a study carried out by Iwaasa et al. (2009), who collected information from three sites; Brandon, MB, Lanigan, SK and Swift Current SK. Stochastic budgets and a simulation model were used to study the economic impact of calving time. In Brandon and Lanigan, It was found that June calving increased net income and was the dominant alternative across all levels of risk aversion, and in Swift Current, June dominated at high-risk aversion levels.

Cow-calf producers in western Canada are faced with many decisions throughout the production cycle. The choice of calving time impacts production rate, marketability of calves, income and expenses and net revenue. The purpose of this study was to determine whether June calving could increase net revenues and be a preferred choice across different risk aversion levels over March calving in western Canada. Data for this study were taken from a study carried out by Iwaasa et al. (2009), who collected information from three sites; Brandon, MB, Lanigan, SK and Swift Current SK. Stochastic budgets and a simulation model were used to study the economic impact of calving time. In Brandon and Lanigan, It was found that June calving increased net income and was the dominant alternative across all levels of risk aversion, and in Swift Current, June dominated at high-risk aversion levels.

Master of Agribusiness / Department of Agricultural Economics / Elizabeth Yeager / Crossbreeding has long been promoted as the preferred method of production for cow-calf producers. Unfortunately, crossbreeding can add complexity to maintain a consistent cowherd and can drive the need to purchase replacement females from outside the producer’s own herd. This has led some producers to pursue straightbreeding to provide their own supply of replacements and the opportunity to more narrowly select for individuals suited to a carcass quality grid marketing system. The subject of this thesis is a Red Angus based cowherd that breeds females to Red Angus sires in early parities. The same cowherd is bred to Simmental sires in later parities to produce a terminal F1 cross. It is the objective of this thesis to explore whether this operation’s straghtbred or crossbred calf crop provides an economic advantage to the other treatment. Mortality data were collected during pre-weaning for both steers and heifers. Mortality data were collected for steers during backgrounding and feedlot phases. Wean weights and feed conversion performance during the backgrounding phase was unavailable for use in this study. Feedlot and carcass data were captured for steers from both treatments. The straightbred treatment showed an advantage in carcass quality. The composite treatment showed a slight advantage in mortality cost during pre-weaning and feedlot phase, and a slight advantage in feed conversion and cost per pound of gain while in the feedlot. The composite treatment showed a significant disadvantage during the backgrounding phase. The primary advantage for the composite treatment was the difference in actual wean weights. This difference in wean weight carried over to a higher start weight during the feedlot phase. This was the driving factor in providing the composite group the economic advantage in this study and making it the more attractive production option.

Optimizing forage productivity is essential to reduce pasture seasonality and ensure available forage to meet the nutritional needs of livestock. This study explores the risk-buffering ability of warm-season forages to fill the summer slump gap in production of cool-season grasses. Small plot experiments were initiated in summer of 2008 in Kentland Farm, Northern Piedmont AREC and Shenandoah AREC, Virginia. Treatments included endophyte-infected tall fescue (KY31 E+), endophyte free tall fescue (KY31 E-), novel endophyte tall fescue (MaxQ), Crabgrass in combination with endophyte-infected tall fescue, Teff, Bermudagrass (BG), and Caucasian bluestem (CB). Plots were harvested May through October of 2009 and 2010 at the late boot stage at a cutting height of 10cm. Subsamples were analyzed for dry matter and nutritive value. To assess risk, bootstrap distributions of biomass and quality data were generated by Monte Carlo simulation and compared against an objective function defined as 59 kg ha-1 d-1 forage yield; 10% CP; 60% TDN. Regardless of variability, warm-season grasses produced biomass yields and nutritional values adequate to fill the summer slump from cool-season forages and demonstrated a higher probability of meeting the minimum requirements in July, August and September. Teff was most consistent in meeting the minimum requirements in mid-summer. However, with good conditions for establishment, both BG and CB can help to fill the gap in summer months when compared to cool-season tall fescue. Bootstrap distributions provide producers with a tool that links their production goals with a measurable value of production risk. / Master of Science

Johne’s disease (JD) in cattle is a disease of economic importance caused by Mycobacterium avium subspecies paratuberculosis (MAP). Studies were conducted to estimate the losses due to lower weaning weight of beef calves from MAP test-positive dams, to compare the perceptions of producers and veterinarians on the burden and economic aspects of MAP infection in cow-calf herds, and to evaluate whether testing and culling MAP test-positive cows is economically beneficial. Calves from cows with strong-positive ELISA results were 21.5 kg lighter at weaning compared to calves from ELISA-negative cows. Calves from heavy MAP shedding cows were 58.5 kg lighter, and calves from moderate shedders were 40.8 kg lighter compared to the calves from fecal-culture negative cows. Based on average feeder calf value during 2007 to 2012, these losses corresponded to US $57 per calf for ELISA strong-positive dams, US $157 per calf for heavy fecal shedder dams, and US $109 per calf for a moderate fecal shedder dam. Seedstock producers and the producers enrolled in control programs were more likely to have MAP uninfected herds. The average prevalence reported by producers was 0.8%. Compared to the small herds (<50 head), the average test-positive percentages and estimated prevalences were reported to be higher in medium (50-149) and highest in large (≥150) herds. Veterinarians reported an overall animal level prevalence in their client herds of 5%. Seedstock herds had a lower prevalence and these producers were more likely to enroll in a JD control program. Income lost due to the presence of JD in an infected cattle herd was perceived to be higher by veterinarians. Compared to the veterinarians, seedstock producers were more likely to perceive genetic losses due to culling MAP positive cows. Average annual loss due to JD in a 100 cow herd with a 7% MAP prevalence was $1,644 and $1,747 based on information provided by producers and veterinarians, respectively. Herd level production decreased with increasing prevalence. Compared to test and cull after ELISA or ELISA followed by fecal culture, using fecal culture alone provided the fastest reduction in herd prevalence. Fecal culture was also the least costly alternative based on long-term cumulative costs of an annual test and cull program. Results from the current study suggest that although testing provides faster progress, limiting within herd transmission by sale of all weaned calves and purchasing only low-risk replacements can also reduce prevalence. Results suggest that MAP infection in cows causes significant losses for the calves that are produced. While the knowledge about JD varied between producers and veterinarians, seedstock producers were more enthusiastic about MAP control programs and had lower MAP prevalence in their herds. Overall losses due to MAP infection in the herd might be substantial. It is very costly to control or eliminate MAP once the infection is established in a herd.

The goal of a cow-calf producer is to produce a calf each year per cow. Research suggests that first year heifers struggle breeding back with their second calf because of the adjustments to new range/main herd conditions and the partitioning of nutrients between gaining weight, milk production, and gestation. This study was conducted at the V-V ranch at the University of Arizona for five years and looked at the effects on young cows when calves were weaned from first year heifers at 80 days rather than 205 days. Early weaning allows for gestational benefits because they are given the opportunity to adapt to herd conditions by applying feed resources to the in utero fetus and their own body condition rather than lactation. All first year heifers were included over three years, and were randomly assigned to two groups, normal weaning (NW) or early weaning (EW). This resulted in 122 heifers in the group whose calves were EW and 119 heifers in the group whose calves were NW. Heifers that were in the EW group bred back at a 27% higher rate in their second year, and had 15% greater longevity in the herd. Calves that were in utero when the nursing calves were early weaned were 16.4 kg heavier at weaning. Part of this was due to the age of the calf and part to gestational health. Early weaning was an effective strategy for improving reproductive performance of first year heifers as well as their survival rate in the herd to 5 years of age. It also resulted in improved performance for their in utero calves.

Beef cattle production in the southeastern United States differs in size, practice, and production type from other U.S. regions. Smaller, cow-calf type operations dominate in this region because the climate, forage availability, and other land use practices of farmers make this type of cattle operation more ideal for the Southeast. This research summarizes the current practices and characteristics that define the Southeastern cow-calf operation of today’s market and operating environment; it also examines the factors that influence the variability of beef production in these operations. Results indicate the following major points: 1.) 53.0% of respondents with commercial cows have fewer than 50 head. 2.) Weaning weight and its variability tend to increase as calves get older. 3.) Calves on seedstock operations wean heavier than those typical of cow-calf operations. 4.) Operators that are more financially invested in their operation seem to be more attentive to outcomes of their production process.