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    Clinical impact of Mycoplasma bovis on New Zealand cattle farms : a thesis presented in partial fulfilment of the requirements for the degree of MVS in Veterinary Science at Massey University, Palmerston North, New Zealand. PERMANENT EMBARGO.
    (Massey University, 2019) Hamill, Carolyn Louise
    Mycoplasma bovis was diagnosed for the first time in New Zealand in July 2017 after an outbreak of non-responsive mastitis and arthritis in a dairy herd in North Otago. Subsequent tracing by Ministry for Primary Industries (MPI) found a network of infected farms in multiple regions around New Zealand, predominantly in the South Island, and a decision was made to eradicate M. bovis through testing and slaughtering. This thesis summarises a herd-level observational case study of 69 infected properties (IPs) New Zealand-wide. The survey was conducted in 2018/19 with the aim of determining the clinical and subclinical impact of M. bovis on cattle farms, including dairy herds and calf/drystock properties. Data were collected on the incidence of clinical disease known to be caused by M. bovis such as refractory mastitis, arthritis, pneumonia and otitis media, as well as morbidity and mortality rates. The association between the subclinical effects of M. bovis on milk production, somatic cell count and antimicrobial usage was also examined on a seasonal basis. Data was then compared with data from seasons before and after the introduction of M. bovis as a within-farm control. In addition, factors that may have had an effect on disease severity were investigated. Farms were surveyed through questionnaires, veterinary sales records, milk production data and laboratory testing results. Clinical disease attributable to M. bovis was not widespread. On drystock properties, little clinical disease caused by M. bovis was confirmed, although many infected calf-rearing enterprises experienced respiratory and gastrointestinal disease secondary to other pathogens. Clinical disease was also rare on dairy farms, but when present it was severe. Two multi-platform dairy herds showed severe non-responsive multiple quarter mastitis, both in dry and lactating cows. One of these affected herds also displayed severe arthritis in milking cows and experienced an uncommon presentation of disease in calves characterised by prematurity, neurological signs and failure to thrive accompanied by arthritis. Compared to milk production prior to exposure to M. bovis, milk production on infected dairy farms did not significantly decrease after exposure. Bulk tank somatic cell count levels and restricted veterinary medicine (RVM) sales across all farms did not show a significant increase after M. bovis infection. The results of this survey could be built upon using longitudinal studies with larger sample size to further assess the impact of M. bovis infection on subclinical disease in New Zealand cattle at both the cow and herd level.
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    Nitrification rate in dairy cattle urine patches can be inhibited by changing soil bioavailable Cu concentration
    (Elsevier, 17/01/2023) Matse D; Jeyakumar P; Bishop P; Anderson C
    Ammonia oxidation to hydroxylamine is catalyzed by the ammonia monooxygenase enzyme and copper (Cu) is a key element for this process. We investigated the effect of soil bioavailable Cu changes induced through the application of Cu-complexing compounds on nitrification rate, ammonia-oxidizing bacteria (AOB) and archaea (AOA) amoA gene abundance, and mineral nitrogen (N) leaching in urine patches using the Manawatu Recent soil. Further, evaluated the combination of organic compound calcium lignosulphonate (LS) with a growth stimulant Gibberellic acid (GA). Treatments were applied in May 2021 as late-autumn treatments: control (no urine), urine-only at 600 kg N ha-1, urine + dicyandiamide (DCD), urine + co-poly-acrylic-maleic acid (PA-MA), urine + LS, urine + split-application of LS (2LS), and urine + combination of GA plus LS (GA + LS). In addition, another four treatments were applied in July 2021 as mid-winter treatments: control, urine-only at 600 kg N ha-1, urine + GA, and urine + GA + LS. Soil bioavailable Cu and mineral N leaching were examined during the experimental period. The AOB/AOA amoA genes were quantified using quantitative polymerase chain reaction. Changes in soil bioavailable Cu across treatments correlated with nitrification rate and AOB amoA abundance in late-autumn while the AOA amoA abundance did not change. The reduction in soil bioavailable Cu induced by the PA-MA and 2LS was linked to significant (P < 0.05) reduction in mineral N leaching of 16 and 30%, respectively, relative to the urine-only. The LS did not induce a significant effect on either bioavailable Cu or mineral N leaching relative to urine-only. The GA + LS reduced mineral N leaching by 10% relative to LS in late-autumn, however, there was no significant effect in mid-winter. This study demonstrated that reducing soil bioavailable Cu can be a potential strategy to reduce N leaching from urine patches.
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    An empirical analysis of the cost of rearing dairy heifers from birth to first calving and the time taken to repay these costs
    (Cambridge University Press, 8/02/2017) Boulton AC; Rushton J; Wathes DC
    Rearing quality dairy heifers is essential to maintain herds by replacing culled cows. Information on the key factors influencing the cost of rearing under different management systems is, however, limited and many farmers are unaware of their true costs. This study determined the cost of rearing heifers from birth to first calving in Great Britain including the cost of mortality, investigated the main factors influencing these costs across differing farming systems and estimated how long it took heifers to repay the cost of rearing on individual farms. Primary data on heifer management from birth to calving was collected through a survey of 101 dairy farms during 2013. Univariate followed by multivariable linear regression was used to analyse the influence of farm factors and key rearing events on costs. An Excel spreadsheet model was developed to determine the time it took for heifers to repay the rearing cost. The mean±SD ages at weaning, conception and calving were 62±13, 509±60 and 784±60 days. The mean total cost of rearing was £1819±387/heifer with a mean daily cost of £2.31±0.41. This included the opportunity cost of the heifer and the mean cost of mortality, which ranged from £103.49 to £146.19/surviving heifer. The multivariable model predicted an increase in mean cost of rearing of £2.87 for each extra day of age at first calving and a decrease in mean cost of £6.06 for each percentile increase in time spent at grass. The model also predicted a decrease in the mean cost of rearing in autumn and spring calving herds of £273.20 and £288.56, respectively, compared with that in all-year-round calving herds. Farms with herd sizes⩾100 had lower mean costs of between £301.75 and £407.83 compared with farms with <100 milking cows. The mean gross margin per heifer was £441.66±304.56 (range £367.63 to £1120.08), with 11 farms experiencing negative gross margins. Most farms repaid the cost of heifer rearing in the first two lactations (range 1 to 6 lactations) with a mean time from first calving until breaking even of 530±293 days. The results of the economic analysis suggest that management decisions on key reproduction events and grazing policy significantly influence the cost of rearing and the time it takes for heifers to start making a profit for the farm.