• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 111
  • 96
  • 43
  • 33
  • 26
  • 22
  • 19
  • 12
  • 5
  • 5
  • 3
  • 2
  • 2
  • 2
  • 1
  • Tagged with
  • 455
  • 191
  • 105
  • 73
  • 57
  • 54
  • 48
  • 48
  • 43
  • 42
  • 42
  • 30
  • 30
  • 28
  • 27
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

BOVINE BENEFACTORIES: AN EXAMINATION OF THE ROLE OF RELIGION IN COW SANCTUARIES ACROSS THE UNITED STATES

Berendt, Thomas January 2018 (has links)
This study examines the growing phenomenon to protect the bovine in the United States and will question to what extent religion plays a role in the formation of bovine sanctuaries. My research has unearthed that there are approximately 454 animal sanctuaries in the United States, of which 146 are dedicated to farm animals. However, of this 166 only 4 are dedicated to pigs, while 17 are specifically dedicated to the bovine. Furthermore, another 50, though not specifically dedicated to cows, do use the cow as the main symbol for their logo. Therefore the bovine is seemingly more represented and protected than any other farm animal in sanctuaries across the United States. The question is why the bovine, and how much has religion played a role in elevating this particular animal above all others. Furthermore, what constitutes a sanctuary? Does not the notion of a sanctuary denote a religious affiliation to salvation and sanctity, and as such are bovines so sacred that they need sanctuaries? Or is it simply that they are so exploited by the livestock industry that they, above all other animals, need salvation? In such a way, this study asks the question, who is the benefactor: the bovine or the human? I highlight that depending upon the motivation the roles can be reversed, so that at a Hindu based cow sanctuary the cow is the benefactor, venerated in gratitude for the numerous gifts it bestows upon us. However, at the Vegan inspired cow sanctuaries it is the human who takes on the role of the “bovine benefactor,” for they are specifically looking to protect and offer bovines sanctuary so that they can lead an autonomous life free from exploitation. I have therefore coined the term “bovine benefactories” to refer not only to the sanctuaries where are they are venerated and protected, but also as an apt juxtaposition to the ‘fear factories’ where the bovines are made to suffer – fear factories being a more figurative name for what the industry labels as CAFOs (concentrated animal feeding operations). At the heart of this study is therefore an emphasis upon the stark juxtapositions and contradictions that Americans have with the bovine. What is deemed holy by one bovine sanctuary is deemed profane by another. At the same time, all bovine sanctuaries stand united in complete contrast to the present-day treatment of bovines within the livestock industry. Furthermore, there is an intriguing juxtaposition between America’s reliance and infatuation with beef and dairy products and their treatment of the bovine. For what is deemed more holy to Americans than the hamburger? As such, I also question whether such a dependence and passion for bovine products is a form of religious expression in itself? This study therefore analyzes to what extent food is deemed sacred to a diverse American public. For example, is the bovine sacred to a secular America because it is their ultimate benefactor? As such, this study looks to deconstruct and question what constitutes bovine veneration, highlighting that the bovine is not only venerated for its virility, aggression, and abundance, but that it has also taken on new significance as a symbol for exploitation, consumerism, and speciesism. In such a way, I highlight that there are many different religious motivations for protecting and offering bovines sanctuary. While some seek to venerate and use the bovine as a symbol, others seek to award the bovine its own autonomy – whereby it is not merely a symbol, but also an animal, with its own identity, will, and purpose beyond that of the human. This work therefore stands squarely on the shoulders of many postmodern and critical theorists that have come before me, from Judith Butler and Rebecca Alpert to Clifford Geertz and David Chidester. Their work has demonstrated that all constructs are limited by presuppositions of what is considered to be the normative – and as such, what is religion and what is deemed sacred is relative to both the individual and the community that one seeks to identify with. In such a way, I shall conclude that the largescale rearing of bovine, the mass producing and consuming of beef and dairy products, and indeed the offering of sanctuary to the bovine can all be analyzed and interpreted as unique, and at the same time intertwined, forms of religious expression and practice. / Religion
22

Nitrogen Efficiency and Regulation of Protein Synthesis in Lactating Dairy Cows

Rius, Agustin Gregorio 01 June 2009 (has links)
Dairy herds are major contributors to N pollution because 70% of the N intake is lost to the environment and 30% or less is retained in milk protein. Plasma amino acids (AA) that are not used for protein synthesis in mammary glands (MG) are catabolized in post splanchnic tissues (liver plus gastrointestinal tract, pancreas, spleen, portal system, and associated adipose tissue) and two thirds of the net supply of essential AA (EAA) are cleared in splanchnic tissues. Thus, increasing AA capture in MG would be expected to reduce AA catabolism and thereby increase efficiency of AA utilization. The objectives of the work presented in this dissertation were to test the effect of energy and N intake on cell regulatory mechanisms, nutrient kinetics, milk, milk protein yield, and N efficiency in dairy cows. The aim of the first study was to test whether metabolizable protein (MP) and dietary energy exerted independent effects on milk protein synthesis and postabsorptive N efficiency. Forty mid-lactation cows (32 multiparous Holstein and 8 primiparous Holstein x Jersey cross-breds) were used in a complete randomized design with a 2 x 2 factorial arrangement of diets. Cows were assigned to one of four dietary treatments: high-energy, high-protein (HE/HP); high-energy, low-protein (HE/LP); low-energy, high-protein (LE/HP); and low-energy, low-protein (LE/LP). Energy concentrations were 1.55 (HE/HP and HE/LP) or 1.44 (LE/HP and LE/LP) Mcal NEL/kg DM according to the NRC model. Changes in predicted MP were achieved by feeding diets with 6.6 (HE/HP and LE/HP) or 4.6% (HE/LP and LE/LP) ruminally undegradable protein (DM basis). Ruminally degradable protein was held constant at 10.1% of DM. All cows were fed HE/HP diet from day 1 to 21 followed by the respective treatments from day 22 to 43 (n=10). Milk protein yield was reduced as dietary energy was reduced. There were no interactions between dietary energy and protein for either milk or protein yield. Milk urea N was significantly affected by energy and protein with an interaction (HE/HP=17.2, HE/LP=12.2, LE/HP=21.0, LE/LP=12.2 mg/dl). Nitrogen efficiency was affected by energy and protein supplies with no interaction and ranged from a low of 31% (LE/HP) to a high of 43% (HE/LP). Although energy and protein independently affected milk and protein yield the tissue and cellular mechanisms that regulate milk production were not studied. The second experiment studied cellular mechanisms in MG that contributed to the regulation of protein synthesis in the presence of energy or protein supply. We hypothesized that metabolism of AA in the MG is controlled by systemic and local tissue adaptations and when combined with altered mammary cell function controlled milk protein yield. Six primiparous mid-lactation Holstein cows with rumen cannulas were randomly assigned to abomasal infusions of casein and starch using a 2 x 2 factorial arrangement. The design was a replicated incomplete 4 x 4 Latin-square. All animals received the same basal diet (17.6% CP and 1.58 Mcal NEL/kg DM) throughout the study. Cows were restricted to 70% of ad libitum intake and infused abomasally for 36 h with water, starch (2 kg/d), casein (0.86 kg/d), or the combination (2 kg/d starch + 0.86 kg/d casein) using peristaltic pumps. Milk weights, milk samples, and arterial and venous blood samples were collected during the last 8 h of infusions. Mammary biopsy samples were collected and tissue protein prepared to evaluate cell signaling. Animals infused with casein had increased arterial concentrations of NEAA and EAA, as well as net uptake and clearance; however, milk protein yield did not increase. Animals infused with starch however, exhibited reduced arterial concentrations of NEAA and EAA but increased clearance and net uptake of most AA. Additionally, infusions of starch increased circulating concentration of insulin, IGF-I, and glucose as well as the rate of mammary plasma flow. Abomasal infusions of starch activated mammary activity of ribosomal protein S6 irrespective of other treatments. However, mammary tissue mTOR increased activity in response to casein only when starch was present during the infusions. These results suggest that cell signaling activation responded to different nutritional stimuli. Milk and protein yield increased in animals infused with starch. Therefore, MG positively responded to energy supply and engaged local and intracellular regulatory mechanisms to achieve that response. Understanding these adaptations could be beneficial in the development of mathematical representations for nutrients utilization in lactating animals. These two studies supported our hypotheses that regulatory mechanism are activated during limiting supply of AA to sustain protein synthesis in MG. The accuracy of mathematical models for lactating animals would increase if effects of energy on AA metabolism and cell signaling related to protein synthesis were included in the representation of milk protein synthesis. / Ph. D.
23

Effect of selecting for 'robustness' on temperament in dairy cows

Gibbons, Jennifer M. January 2009 (has links)
Increased rates of involuntary culling as a consequence of poorer health and fertility had led to the conclusion that dairy cows appear to be less “robust” or adaptable than in the past. A way to address these concerns in breeding programs could be to select for health and welfare by including appropriate traits in a broader breeding index. However, it is important to consider any consequences that such breeding goals may have on dairy cow temperament and welfare. There were two phases to this study. The main objective of phase I was to develop tests for measuring responsiveness to humans and novelty, aggression at the feedface and sociability in dairy cows for use on commercial farms. To allow these tests to be used on commercial farm, they must be short in duration, non-invasive and not disruptive to the daily farming routine, while at the same time allowing comparisons between an individual cow’s responses in a number of similar situations. Results from this study suggested that a standardised human approach test and a stationary visual object are reliable tests for measuring responsiveness of dairy cows to changes in their environment. Measuring behaviour at the feedface proved to be an effective measure of between cow aggression. Inter-animal distance, position in relation to the herd, behavioural synchrony and presence at the feedface proved accurate measures of sociability. The remaining part of the study (Phase II) focussed on assessing how the implantation of a breeding index can affect the temperament of dairy cows on commercial farms. The tests developed were then recorded on 402 first lactation Holstein-Friesian dairy cows selected from sires that scored high (HI) and low (LO) for robustness (health, fertility and longevity traits) to produce two treatment groups on 33 commercial farms. For the purpose of this thesis, only the results from the assessment of aggressiveness are presented. Continuous focal sampling was used to record aggressive behaviour during feeding of the HI and LO cows within the herd. Cows from the HI group were involved in more aggressive interactions, initiated more aggression and received more aggression than cows from the LO group. There was a strong influence of management factors influencing aggression such as the quality of stockmanship, feedface design and nutrition. In conclusion, daughters from sires scoring high for robustness may be expressing a greater ability to maintain position at the feedface during an aggressive interaction. This highlights the importance of assessing the correlated effects of selective breeding, in this case for robustness, on behavioural traits.
24

A Comprehensive Analysis of Novel Dairy Cooling Systems, Their Cooling Efficiency and Impact on Lactating Dairy Cow Physiology and Performance

Ortiz de Janon, Xavier Alejandro January 2016 (has links)
Cooling systems used to reduce heat stress in dairy operations require high energy, water usage, or both. Steady increases in electricity costs and reduction of water availability and an increase in water usage regulations require evaluation of passive cooling systems to cool cows and reduce use of water and electricity. A series of experiments were conducted to evaluate the use of heat exchangers buried as components in a conductive system for cooling cows. In the first experiment six cows were housed in environmentally controlled rooms with tiestall beds, which were equipped with a heat exchanger and filled with 25 cm of either sand or dried manure. Beds were connected to supply and return lines and individually controlled. Two beds (one per each kind of bedding material) constituted a control group (water off), and the other 4 (2 sand and 2 dried manure) used water at 7°C passing through the heat exchangers (water on). The experiment was divided in 2 periods of 40 d, and each period involved 3 repetitions of 3 different climates (hot and dry, thermo neutral, and hot and humid). Each cow was randomly assigned to a different treatment after each repetition was over. Sand bedding remained cooler than dried manure bedding in all environments and at all levels of cooling (water on or off). Results from this experiment demonstrated that bed temperatures were lower and heat flux higher during the bed treatment with sand and water on. We also detected a reduction in core body temperatures, respiration rates, rectal temperatures, and skin temperatures of those cows during the sand and water on treatment. Feed intake and milk yield numerically increased during the bed treatment with sand and water on for all climates. No major changes were observed in the lying time of cows or the composition of the milk produced. The efficiency of conductive cooling as a heat abatement technique in dairy production is highly correlated with the distance between the cooling system and the skin of the cow and the type of bedding material used. A second experiment was conducted to identify possible improvements in the utilization of conductive cooling for cooling cows. Heat exchangers buried 12.7 cm below the surface as components in a conductive system ware evaluated in this study. Six cows were housed in environmentally controlled rooms with tie-stall beds, which were equipped with a heat exchanger and filled with 12.7 cm of either sand or dried manure. Beds were connected to supply and return lines and individually controlled. Two beds (one per bedding material type) constituted a control group (water OFF), and the other four (two sand and two dried manure) used water at 7°C passing through the heat exchangers (water ON). The experiment was divided into two periods of 40 days and each period involved three repetitions of three different climates hot dry (HD), thermo neutral(TN) and hot humid (HH). Each cow was randomly assigned to a different treatment after each repetition was over. The sand and water on treatment was the most efficient treatment under heat stress conditions (humid or dry heat). Cows in stalls with the sand and water on treatment demonstrated lower rectal temperatures, respiration rates, skin surface temperatures and core body temperatures compared to the other three treatments. Additionally, the sand and water on treatment increased milk yield and resting time of cows under heat stress. Also, the sand and water on treatment had the lowest bed surface temperatures and highest heat exchange compared to the other treatments. From these two experiments we confirm that heat exchangers are a viable heat abatement technique that could reduce the heat load of heat stressed cows; however, this system should be paired with additional cooling systems (e.g. fans and or misters) to most efficiently reduce the negative effects of heat stress on dairy production. Additionally, Sand was superior to dried manure as a bedding material in combination with heat exchangers. To make further recommendations of the use of heat exchangers in commercial dairy farm, a third study was developed. Based on the data obtained in the previous experiments, a comprehensive energy balance was developed to fully understand conductive cooling in two different environments (HD and HH), two bedding materials (sand and dried manure) and two depths between cows and the heat exchangers (25 vs. 12.5 cm). The energy balance estimates indicated that sand is the most efficient bedding material when utilized as bedding material with conductive cooling in both hot dry and hot humid environments. In the hot-dry environment there was an increase in the conductive heat exchanged with the reduction in bedding depth to 12.5 cm, however this did not result in a reduction in the heat storage of cows. In the hot-humid environment when heat exchangers were placed 12.5 cm from the top of the bed there was an increase in both the conductive heat loss and heat storage of cows when compared to 25 cm. Additionally, results demonstrated that the efficiency of heat exchangers as measured by heat flux was improved when heat exchangers were at a depth of 12.5 cm. The sensibility analysis indicated that a reduction in the depth and/or an increase in the thermal conductivity of both bedding materials would maximize conductive heat exchange. These results should be utilized as recommendations for the utilization of heat exchangers and conductive cooling in commercial dairy farms. Evaporative cooling is widely used in dairy farms located in arid environments. Even though, these cooling systems have been shown to effectively reduce the heat stress of lactating dairy cows, a growing shortage of water and rising cost of electricity compromise its future usage. An experiment was developed to compare two evaporative cooling systems, their interaction with lactating dairy cows and their usage of natural resources. The efficacy of 2 evaporative cooling systems (Korral Kool, KK, Korral Kool Inc., Mesa, AZ; FlipFan dairy system, FF, Schaefer Ventilation Equipment LLC, Sauk Rapids, MN) was estimated utilizing 400 multiparous Holstein dairy cows randomly assigned to 1 of 4 cooled California-style shade pens (2 shade pens per cooling system). Each shaded pen contained 100 cows (days in milk = 58 ± 39, milk production = 56 ± 18 kg/d, and lactation = 3 ± 1). Production data (milk yield and reproductive performance) were collected during 3 months (June–August, 2013) and physiological responses (core body temperature, respiration rates, surface temperatures, and resting time) were measured in June and July to estimate responses of cows to the 2 different cooling systems. Water and electricity consumption were recorded for each system. Cows in the KK system displayed slightly lower respiration rates in the month of June and lower surface temperatures in June and July. However, no differences were observed in the core body temperature of cows, resting time, feed intake, milk yield, services/cow, and conception rate between systems. The FF system used less water and electricity during this study. In conclusion, both cooling systems (KK and FF) were effective in mitigating the negative effects of heat stress on cows housed in arid environments, whereas the FF system consumed less water and electricity and did not require use of curtains on the shade structure. Results of this research indicate that effective use of conductive cooling in combination with efficient evaporative cooling systems offer opportunities to reduce both water and electricity consumption on dairy farms under both hot dry and hot humid environments.
25

The voluntary intake of silage by individual dairy cows housed in groups

Jackson, D. A. January 1988 (has links)
No description available.
26

Bioactive nutrients for improved metabolic function of dairy cattle

Olagaray, Katie E. January 1900 (has links)
Master of Science / Department of Animal Sciences and Industry / Barry J. Bradford / Dairy cows undergo many homeorhetic adaptations during the transition to lactation. Although many of the physiological processes - including increased lipolysis and postpartum inflammation - are adaptive, exaggerated responses can contribute to metabolic disease and reduced milk production. L-carnitine has been shown to increase hepatic oxidation of fatty acids and reduce hepatic lipid accumulation in early lactation cows; however, L-carnitine is degraded in the rumen. An experiment using 4 ruminally-cannulated Holstein heifers in a split plot design demonstrated that the relative bioavailability of L-carnitine was greater when delivered abomasally than ruminally. There was a dose × route interaction and a route effect for increases in plasma carnitine above baseline, with increases above baseline being greater across all dose levels (1, 3, and 6 g L-carnitine/d) when infused abomasally compared to ruminally. A second experiment used 56 lactating Holstein cows in a randomized complete block design to evaluate 2 rumen-protected products (40COAT and 60COAT) compared to crystalline L-carnitine at doses targeting 3 and 6 g/d carnitine. Although crystalline and 40COAT were effective in linearly increasing carnitine concentrations, only subtle responses were seen for the 60COAT, which were less than that for crystalline carnitine in plasma, milk, and urine. Ineffectiveness of rumen-protected products to increase carnitine concentrations beyond crystalline may have been due to over-encapsulation that hindered liberation of the carnitine and its absorption in the small intestine. Although L-carnitine has the potential to reduce postpartum hepatic lipidosis, effective rumen protection of L-carnitine while maintaining intestinal availability needs further investigation. Plant polyphenols have anti-inflammatory properties and when administered during the transition period, have been shown to increase milk production. An experiment used 122 multiparous Holstein cows in a randomized block design to determine the effect of short term (5-d; SBE5) and long term (60-d; SBE60) administration of Scutellaria baicalensis extract (SBE)on whole-lactation milk yield, 120-d milk component yield, and early lactation milk markers of inflammation. Whole-lactation milk yield was increased for SBE60 compared to control, but was not different for SBE5 compared to control. Greater total pellet intake, milk lactose yield, and reduced SCC during wk 1-9 for SBE60 compared to control, all could have contributed to the observed sustained increase in milk yield. Milk production parameters were not different for SBE5 compared to control. No treatment effects were observed for BCS or milk markers of inflammation (haptoglobin) and metabolic function (β-hydroxybutyrate). Overall, long term administration of S. baicalensis effectively increased milk production, however the mechanism by which this was achieved is unknown. Although routes of administration to effectively achieve their physiological responses were different between L-carnitine (abomasal delivery) and SBE (feeding), both bioactive nutrients can improve the metabolic function of early lactation dairy cows.
27

Circulating microRNAs as biomarkers of reproductive status in the cow

Ioannidis, Jason January 2017 (has links)
Poor reproductive performance is a major challenge for the bovine dairy industry, with implications for profitability and animal welfare. Early pregnancy diagnosis and accurate oestrus detection can improve reproductive performance through efficient herd management. However currently available methods do not allow this. Circulating microRNAs (miRNAs) have been proposed as non-invasive biomarkers of reproductive status in humans. The hypothesis for this work was that differentially expressed miRNAs in plasma will be detectable during early pregnancy / oestrus, which may provide novel potential biomarkers. Using sequencing and PCR-based platforms I successfully identified and validated increases in miR-26a and the miR-26a / miR-205 ratio as early as Day 8 of pregnancy (max. 7.5-fold) in the plasma of pregnant compared to non-pregnant heifers. These miRNAs are known regulators of immunity, angiogenesis and metabolism, however their specific roles in early pregnancy remain to be investigated. I also identified small but significant increases in the levels of miR-125b, let-7f, miR-145 and miR-99a-5p at oestrus, when compared with the luteal phase of the cycle. These miRNAs have been previously shown to regulate the follicular to luteal transition in the bovine ovary. Finally, I provide a validated high-throughput resource which can help identify potential global biomarkers of tissue function, as shown for the liver-enriched miR-802 in the present results. The findings of this work may be useful in the development of diagnostic methods for early pregnancy and oestrus, and pave the way for the functional characterisation of these miRNAs in bovine reproduction.
28

Comparison of F1 cows sired by Brahman, Boran and Tuli bulls for reproductive, maternal, and cow longevity traits

Maiga, Assalia Hassimi 25 April 2007 (has links)
Birth weight (BW) (n =1277) and weaning weight (WW) (n = 1090) of calves, pregnancy rate (PR) (n = 1386), calf crop born (CCB) (n = 1386), calf crop weaned (CCW) (n = 1294), cow’s weight at palpation (CW) (n = 1474) and cow body condition score (BCS) (n = 1473) were evaluated from 1994 to 2006 in 143 F1 cows sired by Brahman (B), Boran (Bo) and Tuli (T) bulls and born to Angus and Hereford cows. Mouth scores (MS) (n = 139) were assigned to the remaining cows in 2004 and 2005. Fixed effects included sire breed of cow, dam breed of cow, and calf’s birth year/age of cow; random effects included cow and sire of cow. BW and WW were evaluated using the same model and adding gender for both and age for WW. All two-way interactions were tested for significance. Calf’s birth year/age of dam was significant for all traits (P < 0.05) except WW. BW for calves out of F1 B, Bo and T bulls were 35.08, 34.76 and 34.87 kg, respectively, and were not different. WW differed (P < 0.05) for calves out of F1 B, Bo and T cows (235.87, 221.10 and 208.35 kg, respectively). PR (0.922, 0.955 and 0.936, respectively), CCB (0.881, 0.931, 0.890, respectively), CCW (0.848, 0.898 and 0.869, respectively), did not differ among F1 B, Bo and T cows. CW when cows were 8- or 9-year old were 600.78, 514.63 and 513.14 kg, respectively, for F1 B, Bo and T cows, with those sired by B being heaviest (P < 0.05). BCS for B-, Bo- and T-sired cows were 5.23, 5.48 and 5.18, respectively, with F1 Bo cows having highest scores. Higher MS (P < 0.05) were assigned to Bo and B-sired cows (0.95 and 0.94, respectively) compared to T-sired cows (0.78), when both broken and solid incisors were scored 1, and smooth scored 0. When both smooth and broken were scored 0, and solid were scored 1, higher scores were assigned to B- (0.53) compared to T-sired cows (0.24), the Bo-sired cows being intermediate. Higher reproductive rates were found for Boran-sired cows, but Brahman-sired cows weaned heavier calves.
29

Evaluation Of the NRC 1996 winter feed requirements for beef cows In western Canada

Bourne, Jodi Lynn 28 February 2007
A trial was conducted to evaluate the accuracy of the 1996 NCR beef model to predict DMI and ADG of pregnant cows under western Canadian conditions. Over two consecutive years, 90 Angus (587±147 kg) cows assigned to 15 pens (N=6) were fed typical diets ad libitum, formulated to stage of pregnancy. Data collection included pen DMI and ADG (corrected for pregnancy), calving date, calf weight, body condition scores and ultrasound fat measurements, weekly feed samples and daily ambient temperature. DMI and ADG for each pen of cows in each trimester was predicted using the computer program Cowbytes based on the 1996 NRC beef model. The results indicate that in the 2nd and 3rd trimester of both years the model under predicted (P≤0.05) ADG based on observed DMI. Ad libitum intake was over predicted (P≤0.05) during the 2nd trimester, and under predicted (P≤0.05) during the 3rd trimester of pregnancy. A second evaluation was carried out assuming thermal neutral (TN) conditions. In this case, it was found that during the 2nd and 3rd trimesters there was an over prediction (P≤0.05) of ADG relative to observed. Under these same TN conditions, the ad libitum intake of these cows was under predicted (P≤0.05) for both the 2nd and 3rd trimesters. These results suggest current energy equations for modelling environmental stress, over predict maintenance requirements for wintering beef cows in western Canada. The results also suggest that the cows experienced some degree of cold stress, but not as severe as modelled by the NRC (1996) equations. Further research is required to more accurately model cold stress felt by mature cattle, and their ability to acclimatise to western Canadian winter conditions.
30

Investigation of antimicrobial resistance and antimicrobial use in western Canadian cow-calf herds

Gow, Sheryl Pamela 19 September 2007
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.

Page generated in 0.0333 seconds