Veterinary Science - Theses
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ItemEffect of feeding slowly fermentable grains as protection against heat stress in ruminants( 2017)The combination of high environment temperatures, the heat increment resulting from feed fermentation and digestion (HI), high metabolic rates and metabolic heat production (HP) make ruminants susceptible to heat stress (HS). The reduction in the ratio forage-to-concentrate in the diet during HS is a traditional nutrition management aimed at increasing the energy content of the diet to compensate for reductions in dry matter intake (DMI) frequently observed in heat stressed ruminants. Wheat is a rapidly fermentable grain commonly used as an energy source for ruminants in Australia. However, the rapid rate of rumen starch fermentation of wheat is associated with rumen acidosis and elevated body temperature in cattle. By contrast, slowly fermentable grains, like corn, are associated with better utilization of metabolisable energy (ME) and reduced HI. Chemical treatment of wheat grains with sodium hydroxide (NaOH) or Bioprotect (BP) may reduce the rate of starch fermentation, HI and metabolic HP. The effect of feeding cereal grains differing in rumen fermentability on physiological, metabolic and productive responses of ruminants under high thermal load has not previously been evaluated. Therefore, it was hypothesised that by feeding slowly fermentable grains, the HI would be reduced, thereby reducing the effects of HS in ruminants. The research presented herein firstly investigated the differences between rapidly (barley and wheat) and slowly fermentable grains (corn, 3 % NaOH- and BP-treated wheat) on gas production kinetic parameters, pH, and starch and dry matter (DM) digestibility using in vitro experiments. Then, using in vivo experiments the effect of feeding either slowly or rapidly fermentable grain diets at different feed intake on HS related changes on physiological, metabolic and digestibility variables of wethers and the physiological, metabolic and productive responses of lactating dairy cows fed grain-based diets differing in grain fermentability during summer were investigated. In vitro experiments demonstrated the slower fermentability and higher pH during incubation of corn, BP- and 3 % NaOH-treated wheat compared with untreated wheat and barley. In vivo experiments demonstrated that HS induces changes in physiological variables, blood-acid base balance, and energy utilization in ruminants; that elevated DMI increases the thermal load of wethers under HS; that feeding wethers either a corn- or 3 % NaOH-treated wheat based diet, may increase the glucose available for intestinal absorption, can reduce the HI and ameliorates the physiological variables negatively affected by HS compared with untreated wheat; that the reduced total apparent starch digestibility of corn diets explains the improved responses observed in corn-diet fed wethers under HS condition; and that feeding 3 % NaOH-treated wheat improves apparent starch, DM digestibility, and DMI of wheat diet without increasing the metabolic HP. In the dairy cow experiment, a lower rectal temperature and higher milk yield was found in cows fed corn diets that were associated with reduced HI and metabolic HP, and higher glucose availability than in cows fed untreated wheat. It was also demonstrated that rumen temperature is a sensitive predictor of core body temperature and physiological and productive variables negatively affected by HS. Thus, this thesis demonstrated that the use of slowly fermentable grains is a viable nutrition management to improve thermo-tolerance of ruminants under high heat loads.
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ItemAnthelmintic resistance in gastrointestinal nematode parasites of dairy cattle in the Macalister irrigation district of Victoria( 2016)Gastrointestinal nematode parasitism is one of the most production limiting diseases of pasture-based dairy enterprises in Australia, in terms of its effect on early lactation milk production and live weight gain of replacement heifers. Farmers are heavily reliant upon the use of anthelmintics to control parasitism, which raises concerns about the development of anthelmintic resistance. Studies in beef cattle in Australia and overseas have demonstrated very high levels of resistance to all available anthelmintic classes. However, there have been no substantial investigations of anthelmintic resistance on dairy cattle farms anywhere in the world. The objective of the first trial was to report anthelmintic resistance in gastrointestinal nematode parasites of cattle on commercial dairy farms in the Macalister Irrigation District of Gippsland, Victoria. Faecal egg count reduction tests (FECRTs) were used to assess anthelmintic resistance on 20 farms between May 2013 and June 2014. All three currently available anthelmintic classes for cattle nematodes in Australia were tested. Faecal samples were collected 10-14 days post-treatment for individual faecal egg counts (FEC) and larval differentiation. The arithmetic mean FEC for each treatment group was compared with an untreated control post-treatment. Resistance was defined as <95% reduction in FEC, with a lower 95% confidence interval <90% when the mean FEC of the control group, differentiated by genus, was greater than 25 eggs/g. Anthelmintic resistance was present on all 20 dairy farms involved in this study. Resistance to doramectin in at least one species was detected on 15/20 (70%) farms, fenbendazole on 16/20 (80%) farms and levamisole on 5/20 (25%) farms. On three farms, resistance by Ostertagia ostertagi to all three anthelmintic classes was detected. This is the first report of anthelmintic-resistant O. ostertagi on Australian dairy farms and is of concern, given the high pathogenicity of this species. There is universal agreement that reliance upon chemical-based parasite control must be addressed in order to ensure the long term sustainability of current and future anthelmintics. One option for reducing the selection pressure for anthelmintic resistance in dairy replacements is the concept of targeting anthelmintic treatments to only those animals that require it, rather than the whole group. The second trial aimed to compare whole group treatment applied at 6-weekly intervals (control) with a live weight gain-based targeted selective anthelmintic treatment (TST) regime, in terms of anthelmintic use and growth performance, using a non-inferiority study design. Four-hundred and thirty heifers were allocated to either a TST or control group according to odd or even ear tag number. Live weights and faecal egg counts were monitored three times over 12 weeks (day 0, week 6, week 12). Heifers in the control group were all treated on each occasion with a subcutaneous injection of moxidectin. Heifers in the TST group were treated only if they failed to achieve a predetermined live weight target calculated for each visit. An arbitrary non-inferiority margin of 10%, considered the largest commercially acceptable difference, was defined a priori and average daily gain (ADG; g/day) for each group was compared statistically. The results showed that ADG of heifers in the TST group were not inferior to whole group anthelmintic treatment and anthelmintic usage was reduced by 48%. This supports the case for a larger scale study of this strategy in Australian dairy herds; particularly since long-term TST in sheep has been shown to slow the development of anthelmintic resistance in the field.
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ItemA novel approach to treating cows with postpartum anoestrus and associated risk factors( 2016)This project combines the findings of two distinct, but related research studies investigating postpartum anoestrus (PPA) in lactating dairy cows. These studies involved five seasonally calving commercial Victorian dairy herds. The first study was completed as a cross-sectional analysis of prevalence and risk factors for PPA on the five herds involved, and the second study was conducted as a clinical trial to investigate the differences in reproductive success of cows with PPA when treated with either a FTAI based protocol, or a protocol that relied on oestrus detection. Study one assessed data from 3,194 cows from within the five herds. Prevalence was calculated as the proportion of animals which were presented for PPA treatment to a veterinarian as a proportion of the total number of cows within herds at the start of each herd’s Mating start date (MSD). Risk factors that were assessed included age, days in milk (DIM), body condition score (BCS), and herd. The outcome of interest for the study was risk of PPA, and this was assessed in a multivariable logistic regression model. Risk factors were reported as adjusted odds ratios from the model, and because a significant interaction terms of BCS x DIM was discovered, these variables were referenced to each other in the model, and the combined variables were reported with predicted probabilities. The average prevalence of PPA across the herds involved was 44%. The association between age and the probability of being diagnosed as anoestrus was greatest for 2-year-old cows with the odds of anoestrus being 2.43 (95% CI 1.80 to 3.27) times greater in this group compared with cows aged 6 years and greater. For cows that were > 90 DIM at MSD, the odds of anoestrus for cows that were < 4.0 BCS was 8.05 (95% CI 3.20 to 20.2) times that of cows that were BCS 4.5 to 5.5. For cows that were > 90 DIM at MSD the odds of anoestrus for cows of BCS ≥ 4.0 to < 4.5 was 2.10 (95% CI 1.25 to 3.54) times that of cows that were BCS 4.5 to 5.5. The highest predicted probability of anoestrus was for cows of BCS < 4.0 that were DIM < 60 at MSD (0.89, 95% CI 0.85 to 0.93). Study two involved a clinical trial with 1,167 cows that were presented for treatment of PPA. This compared Ovsynch + P4 (FIXED) to a protocol that removed the final GnRH injection and instead relied on detection of oestrus (HEAT). The aim of this trial was to determine whether improvements in first service conception rate (FSCR) could be made with an alternative program to Ovsynch + P4, and to assess whether reductions could be made in the proportion of cows with prolonged return to oestrus interval after an unsuccessful insemination. The FSCR for the HEAT treatment group was numerically, but non-significantly, higher than the FIXED treatment group, however this did not result in superior reproductive performance overall, with 49-day pregnancy rates similar between treatment groups. The proportion of cows that had returned to oestrus by 24 days after an unsuccessful insemination differed across the two treatment groups, 46% versus 67% for FIXED and HEAT respectively (χ2 test statistic 25.19; df 1; P < 0.001). When assessed in a Cox proportional hazard regression model, for cows in the HEAT treatment group, the daily hazard of returning to oestrus was 1.75 (95% CI 1.40 to 2.19) times that of cows in the FIXED treatment group. Overall, the studies within this project provided new information regarding prevalence of PPA in seasonally calving Victorian dairy herds, as well as highlighting key risk factors. The clinical trial highlighted that alternative strategies may be implemented to further enhance the reproductive success observed in cows with PPA when treated with an alternative synchrony protocol that does not rely on FTAI.
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ItemDeterminants of reproductive performance of dairy cows in commercial herds in Australia( 2004-06)Reproductive performance of lactating dairy cows was studied using a prospective observational study of 29,462 cows in 168 commercial herds in 9 regions in Australia. There was substantial variation in all reproductive performance measures between herds, suggesting that important increases in reproductive performance would be possible in many commercial Australian herds if causal factors were identified and modified. Multivariable multilevel logistic models were used to study potential determinants for two measures of overall reproductive performance - pregnancy by week 6 after start of the mating period (mating start date or MSD) and non-pregnancy by week 21 after MSD, and for two components of overall reproductive performance - submission by week 3 after MSD and conception to first service.
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ItemThe effects of post-partum and pre-mating start date weight change and production level on reproductive performance in lactating cows in a seasonal calving, pasture-based system( 2013)Retrospective fertility data from a 600 cow, predominantly Holstein-Friesian, seasonal calving herd in south west Victoria was analysed to ascertain fertility trends on the farm over 10 years. Prospectively, daily body weights were collected and analysed with reproductive and production data to establish associations between weight change and production level both post-partum and pre-mating start date and reproductive performance. Body weights from automated walkover weighing scales at the exit to the dairy were collected, filtered and analysed to determine weight change trends post-partum (PP) and pre-mating start date (MSD). Herd reproductive parameters were established from calving dates, AI dates and early ultrasound pregnancy testing results. Production data from inline milk meters were collected and analysed to provide measures of PP and pre-MSD production level. The effects of PP and pre-MSD weight change and production variables on reproductive performance, together with the confounding variables age, time calved and calving induction, were statistically analysed to establish predictors of poor reproductive performance. ACCURACY OF THE SCALES Initially, a study was performed to determine the repeatability of the walkover scales and their agreement with static scales. Forty-six cows from the study herd were weighed once using a set of static scales and repeatedly using the automated walkover weighing system. The walkover weighing system showed substantial agreement with the static scales when assessed using Lin’s concordance correlation coefficient. This contrasted with limited agreement when assessed using Bland and Altman’s method, largely due to poor repeatability. Removal of a single outlier from the data set increased all measures of agreement and repeatability. Cow misbehaviour during walkover weighing accounted for many of the larger weight discrepancies. The limited agreement and poor repeatability suggest that the automated weighing system is inadequate for detecting small body weight differences in individual cows based on comparisons of single weights. Excluding outlier weights and comparing means of 7 consecutive daily weights may improve agreement sufficiently to allow meaningful assessment of small short-term changes in automated weights. WEIGHT CHANGE TRENDS Once an accurate weight dataset was established through data filtration, weight change trends over time were established. Linear regression lines were fitted through all filtered weights recorded between days 8 to 28 and 29 to 49 PP and days 42 to 22 and 21 to 1 pre-MSD. Positive slopes were assigned ‘Up’ trend and negative slopes were assigned ‘Down’ trend resulting in one of four possible double weight trends – Down Down (DD), Down Up (DU), Up Down (UD) and Up Up (UU) - for both PP and pre-MSD weight change. EFFECTS OF WEIGHT CHANGE AND PRODUCTION ON REPRODUCTIVE PERFORMANCE The most important factor affecting reproductive performance was duration of time calved. An increased time from calving to MSD resulted in improved measures of reproductive performance. PP weight change, age and yield at 100 days-in-milk were also significant predictors of submission by 3 weeks with PP DU cows having 1.7 times the odds of being submitted compared to DD cows. Three to 5 year olds had almost 3 times the odds of being submitted compared to 2 year old cows. Producing an extra 100L of milk by 100 days-in-milk resulted in 5% reduced odds of being submitted by 3 weeks. Pre-MSD weight change was a significant predictor of not being in-calf by 21 weeks. Pre-MSD DU, UD and UU cows had reduced odds of not being in-calf compared to DD cows. Cows producing an extra litre of milk daily in the 3 weeks prior to MSD had 5% reduced odds of submission by 3 weeks and 7% increased odds of becoming an NVO. In summary, reduced reproductive performance was observed in first calving heifers, animals not long calved, DD cows and high producing animals. The ability to identify these high risk animals prior to MSD could assist reproductive management, either through modified nutritional supplementation, prompt implementation of hormonal treatments or through alteration of insemination choices. Assessing the efficacy of these suggested management modifications at improving reproductive performance of high risk animals was beyond the scope of this study but provides suggestions for further research.
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ItemThe role of ADAM 12 in determining skeletal muscle development and intramuscular fat deposition in cattle( 2011)The research undertaken throughout this PhD thesis aimed to better understand the cellular mechanisms that influence development of skeletal muscle and intramuscular fat in beef cattle. In particular, I investigated the role of the extracellular matrix protease disintegrin and metalloprotease protein 12 (ADAM 12) in regulating muscle development and intramuscular fat deposition. These experiments sought to determine whether ADAM12 can be used as a potential modulator to manipulate these processes to increase muscling and intramuscular fat (IMF) deposition in cattle. My intital investigation sought to determine if variation in ADAM 12 expression in skeletal muscle was associated with different muscle phenotypes observed in cattle of various breeds. Primary skeletal muscle cells were isolated from Angus (high muscling), Hereford (moderate muscling) and Wagyu cross (X) Angus (low muscling) and grown in culture. The myogenic potential was found to differ between breeds of cattle whereby myoblasts from Angus cattle were found to proliferate at a greater rate than those of Hereford and Wagyu X Angus during early stages of growth (5-20 hours in culture) in vitro. The proliferation rates of myoblasts during early stages of culture in vitro were also found to be positively related to the liveweight of cattle. ADAM 12 gene expression was not found to be related to in vitro proliferation rates, suggesting that its influence on muscling was negligible, or that its expression in in vitro culture conditions was not reflective of its role in development of muscle tissue in vivo. The role of ADAM 12 during fat development was investigated using an in vitro model of adipogenesis, 3T3-L1 cells. ADAM 12 gene expression was knocked down over a 13-day developmental timecourse using Stealth™ RNAi. DNA, RNA and protein samples were collected to closely analyse the effect of ADAM 12 knockdown on proliferation and differentiation of 3T3-L1 cells. ADAM 12 gene knockdown was found to reduce the proliferation and differentiation of 3T3-L1 cells. However, in ADAM 12 knockdown cells enzyme markers of adipogenesis G3PDH (early adipogenic marker- glucose metabolism) and FAS (late adipogenic marker- lipid filling) were found to be greater. This was consistent with the phenotypic observation and morphometric analysis that the ADAM 12 gene knockdown treated cells displayed hypertrophy, with fewer lipids of greater size. Microarray analysis found the pathway most affected by ADAM 12 gene knockdown to be regulation of insulin-like growth factor by insulin‐like growth factor binding proteins which is thought to be responsible for the effect found on proliferation. Adipocytokines such as adiponectin and adipsin were also found to be significantly down‐regulated in ADAM 12 gene knockdown cells. Absence of these adipocytokines, in particular adiponectin, have previously been shown to cause hypertrophy of mature adipocytes due to alterations in insulin‐sensitivity and fatty acid oxidation. Thus ADAM 12 appears to be an important regulator through all stages of fat development (proliferation, differentiation and energy metabolism). Following in vitro experimentation, the role of ADAM 12 in skeletal muscle and intramuscular fat development in vivo was investigated. The m. longissimus dorsi and m. semitendinosus (LD and ST) muscles from five Angus and Brahman cattle were collected for histology and ADAM 12 gene expression analysis. Muscle fibre typing was used to determine if ADAM 12 expression patterns related to differences in skeletal muscle traits, such as muscling and IMF deposition, which are often influenced by proportions of the different muscle fibres. Consistent with other findings, the ST muscle was found to contain a higher proportion of glycolytic myofibres than the LD muscle which contained a greater proportion of oxidative myofibres. ADAM 12 gene expression was also found to be greater in the LD compared with the ST muscle. Fluorescent immunohistochemical (FIHC) staining for ADAM 12 and image analysis found that the relative amount of ADAM 12 distribution to also be greater in the LD muscle. Regression analysis found a positive relationship for the distribution of ADAM 12 against the proportion of type I myofibres (r2 = 0.86, p < 0.05) and a negative relationship for the distribution of ADAM 12 against type IIX myofibres (r2 = 0.82, p < 0.05). The gene expression and regression analysis suggest ADAM 12 is type I myofibre specific in cattle. This was further confirmed by FIHC staining of ADAM 12 with slow myosin heavy chain I (slow MHC-I) with which ADAM 12 co-localised. The type I myofibre specificity of ADAM 12 may be important in the regulation and maintenance slow myofibres in the LD and of IMF deposition, to which proportion or number of type I myofibres have been related to previously. Lastly, the expression profiles of ADAM 12 was investigated in skeletal muscle across a developmental time-course in two cattle breeds with extreme muscle phenotypes, Piedmontese X Hereford (high muscling) and Wagyu X Hereford (high marbling) cattle. Muscle biopsies (from LD muscle) were collected at 3, 12 and 25 months of age. PiedmonteseX cattle contained a greater proportion type IIX, type IIAX and type IIC myofibres compared with WagyuX cattle which had a higher proportion of the more oxidative type I and type IIA myofibres. Gene and protein expression of ADAM 12 was not different between breeds of cattle. However, ADAM 12 gene expression at 3-months of age was found to be positively related to feedlot average daily weight gain (kg/d) (r2 = 0.62, p < 0.05), liveweight at 25-months of age (kg) (r2 = 0.67, p < 0.05), hot carcass weight (kg) (r2 = 0.81, p < 0.05), retail beef yield (kg) (r2 = 0.65, p < 0.05) and eye muscle area (cm2 ) (r2 = 0.77, p < 0.05). These results suggest ADAM 12 is a candidate to be used to predict muscling and beef yield in cattle from a very young age. Analysis of ADAM 12 protein and gene expression found that expression of ADAM 12 in skeletal muscle was elevated at 3-months of age during pre-weaning muscle growth, with reduced expression at 12-months of age. Expression of ADAM 12 in skeletal muscle was upregulated again at 25-months of age, possibly related to its role in IMF deposition and marbling during this stage of growth in cattle. Thus ADAM 12 proves to be an important regulator during muscle development and IMF deposition in cattle and is a candidate to predict beef yield from a very young age. Findings from this PhD thesis show that ADAM 12 may be an important regulator of muscle and marbling development in cattle. The specific association of ADAM 12 with type I myofibres, and its role in signalling adipogenesis as outlined by this PhD thesis and work by others also suggest it is a candidate to increase marbling in cattle. Greater muscling and marbling by modulation of ADAM 12 may improve the quality and value of beef and efficiency of beef production (by increasing beef yield) to enhance competitiveness of Australia’s beef export.