Stanton PhD Thesis final_docx - Atrium - University of Guelph

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When a stressful stimulus occurs, a stress response is initiated via an increase in the cyclic pulsations of corticotrophin releasing hormone (CRH) and arginine-vasopressin neurons of the paraventricular nuclei of the hypothalamus. This activation of the Hypothalamic–Pituitary– Adrenal (HPA) axis results in increased adrenocorticotropic hormone (ACTH) and cortisol secretory episodes. ACTH is the key regulator of glucocorticoid secretions (Tsigos and Chrousos, 2002). Activation of the sympathetic nervous system occurs simultaneously to HPA activation and redirects blood flow from the interior organs of the body to the exterior where it can be used for rapid response in the flight or fight response (as reviewed by Carroll and Forsberg, 2007). There is also a redistribution of leukocytes from various compartments resulting in increased numbers of white blood cells in peripheral circulation. This results in enhancement of the cell mediated immune response as a result of acute stress (Dhabhar and Mcewen, 1997). In the case of chronic stress, there is an increased duration at, which glucocorticoids act. This negates the positive aspects of acute stress on the immune system and results in suppression of interleukin-6 and the cell mediated immune response. This is an adaptive response since repeated stimulation of the HPA axis and the immune system by glucocorticoids could lead to an increased risk of autoimmune disease (Dhabhar and Mcewen, 1997). Chronic stress can lead to decreased growth and performance in livestock (Barnett and Hemsworth, 1986; Hemsworth et al., 2000). Two of the main stressors for the milk-fed calf are nutritional stress and social isolation. Two of the main stressors for the post-weaned calf are social mixing and transport stress. 9
1.4.2 Nutritional Stressors Dairy calves are primarily fed a milk based diet until weaning is initiated. Energy intake in the pre-weaning period is currently recommended to be 4.8-5.3 Mcal/day for a 50 kg calf under thermoneutral conditions in order to gain 1.0 kg/day (Drackley, 2008). The traditional feeding practice for North American calves is to feed 10% of their body weight; a 45 kg calf is fed 4.5 kg of milk. However, recent data from the National Research Council found that 45 kg calves need to consume approximately 2.5L of whole milk for maintenance and the remaining milk can be used for growth (National Research Council, 2001; Drackley, 2008). These calculations are based on a thermoneutral environment , which does not require animals to exert energy to maintain homeostasis; heat or cold can increase the maintenance demands of calves further reducing the energy available for growth on a restricted feeding regime (as reviewed by Drackley, 2008). For this reason, the recommended caloric intake of calves has begun to change, with the National Farm Animal Council’s Code of Practice for Care and Handling of Dairy Cattle recommending calves be fed 20% of their body weight (National Farm Animal Council, 2009). To avoid a post-weaning slump in weight gain when calves transition from a primarily milk based diet to a grain based diet it is essential that their rumen is adequately developed to absorb nutrients from a grain based diet. At birth, a calf’s rumen is small and underdeveloped. Highly fermentable dry feed is necessary for it to develop in size, musculature and absorptive capacity (Davis and Drackley, 1998). It takes approximately three weeks of grain and water intake for the rumen to develop to a size and absorptive capacity that is necessary for maintenance of growth and four months for it to reach the size of a mature animal (Davis and 10
Page 1 and 2: AN EVALUATION OF THE IMPACT OF MANA
Page 3 and 4: differences in weight gain or calf
Page 5 and 6: 3.2.2 Experimental Study Design 68
Page 7 and 8: 7.4.5 Culling and mortality prior t
Page 9 and 10: Table 6.5: Reasons for death loss a
Page 11 and 12: and season as fixed effects and for
Page 13 and 14: , which requires that “all calves
Page 15 and 16: ehaviour of dams challenged with LP
Page 17 and 18: In cattle, early disease detection
Page 19: increased rest and decreased appeti
Page 23 and 24: humans, the metabolic rate increase
Page 25 and 26: Without human intervention, calves
Page 27 and 28: average group size of three or four
Page 29 and 30: al., 2004). Group composition and g
Page 31 and 32: first is the addition of antibiotic
Page 33 and 34: viral diarrhea virus (BVDV) bovine
Page 35 and 36: 1.7 CONCLUSION AND THESIS OBJECTIVE
Page 37 and 38: Buhman, M. J., L. J. Perino, M. L.
Page 39 and 40: Hemsworth, P. H., G. J. Coleman, J.
Page 41 and 42: Schein, M. W. and M. H. Fohrman. 19
Page 43 and 44: Waltner-Toews, D., S. W. Martin and
Page 45 and 46: ehavioural observations ( Borderas,
Page 47 and 48: and had access to ad libitum calf s
Page 49 and 50: may indicate abdominal discomfort,
Page 51 and 52: identified in 5% (40/788) of calves
Page 53 and 54: of diarrhea in calves on this farm
Page 55 and 56: The most common response to the vig
Page 57 and 58: at any observation period. For this
Page 59 and 60: 3 was associated with lower ADG rel
Page 61 and 62: of heifers to allow them to calve a
Page 63 and 64: 2.5 REFERENCES Al-Chaer, E. D. & Tr
Page 65 and 66: Panivivat, R., Kegley, E. B., Penni
Page 67 and 68: Table 2.2: List of exclusions used
Page 69 and 70: Table 2.4: The lsmeans ± S.E. of t
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Figure 2.1: Timeline describing tri
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Proportion of calves performing beh
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in a lower rate of vocalizations an
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sites. During the summer months bot
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treatment and weight gain category.
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pre-weaning calf starter intake, an
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Calves spent a total of 13 ± 6 (me
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calves were still allowed access to
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It was hypothesized that the more t
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calves to consume sufficient calf s
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Table 3.1: Descriptive list of obse
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Number of steps per day 7000 6000 5
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Number of lying bouts per day 35 30
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Weight gain (kgs) first 7 days post
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The concept of separating stressors
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were bedded with straw. While house
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4.2.5 Data Collection Calf starter
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4.3 RESULTS enrolment. On average,
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4.3 DISCUSSION There was no effect
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4.4 REFERENCES Chua, B., E. Coenen,
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Steps per day 2500 2000 1500 1000 5
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Appendix 4.1: Scoring sheet used fo
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positive for M. bovis and 4 differe
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feedlots (Van Donkersgoed, 1992). I
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protocol included the identificatio
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(cases) and two calves closest in a
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No statistical analysis was perform
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5.4.3 Growth Three calves returned
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5.4.4 Testing for Mycoplasma Of the
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may be an early sign of respiratory
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small number of unilateral ear droo
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evaluated for efficacy and carefull
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5.6 REFERENCES Biddle, M. K., L. K.
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USDA. 2007. Dairy 2007, part II: Ch
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Table 5.2: Incidence and median age
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Table 5.4: Breakdown of the number
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Figure 5. 5.1: 1: Images taken from
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6.1 ABSTRACT Bovine respiratory dis
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efore entry into the milking herd o
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with bovine viral diarrhea (BVD). O
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6.3.3 Outcome Measures All calves w
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tests, or multiple partial F-tests,
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The effect of treatment on height a
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this study involved continuing with
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is important to emphasize that the
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6.7 REFERENCES J. Carroll and N.E.
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Table 6.1: Disease variables consid
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Table 6.3: Least squares means ( ±
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Table 6.5: Reasons for death loss a
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CHAPTER 7: THE IMPACT OF BOVINE RES
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7.2 INTRODUCTION Bovine respiratory
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days following study enrolment than
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Age at First Calving Since age at f
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(Weaning, Transition, Grower 1, Gro
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The excluded source farm resulted i
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of calves with BRD60 survived to fi
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7.4.8 Milk Production First Test Da
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BRD before 6 months of age decrease
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BRD following movement to group hou
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calves with BRD60 were 1.5 (95% CI:
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7.7 REFERENCES Correa, M. T., C. R.
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Table 7.1: Calving Ease Scoring Sys
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Table 7.3: Least-square means (± S
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Table 7.5: Proportion of calves sur
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Table 7.7: Producers primary reason
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Table 7.9: Effect of BRD60 on calvi
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Table 7.11: Distribution of heifers
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Figure 7.2: Difference in least squ
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Figure 7.4: Time to event analysis
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CHAPTER 8: CONCLUSIONS AND FUTURE R
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Heifers with poor post-weaning grow
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strategic antimicrobial use was met
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Specifically, How can disease sever
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Does transportation, initial social
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