Les séismes glaciaires ont des magnitudes Mw~5 et sont liés au vêlage d’icebergs instables volumineux (km3). Dans le but de caractériser la force à l’origine des signaux sismiques longue-période (10-100~s) mesurés lors de tels évènements, nous développons une méthode d’inversion de la fonction source et un modèle mécanique numérique du phénomène. Grâce à l’analyse détaillée des histoires de forces inversées, nous mettons en lumière l’existence de plusieurs phénomènes responsables de la génération du signal sismique, à savoir (1) une avalanche de glace déclenchée par le détachement d’un iceberg, (2) le vêlage et le basculement de l’iceberg qui applique une force horizontale normale au glacier, et (3) l’accélération de l’ice-mélange dans le fjord. On montre que la magnitude des séismes glaciaires ne peut être interprétée de manière simple car elle englobe plusieurs processus distincts. D’après les résultats de modélisation numérique, l’amplitude de la force générée par un iceberg tournant contre un terminus ne varie pas de manière linéaire avec le volume de glace mais est largement déterminée par plusieurs facteurs qui influent sur la dynamique du mouvement. Ceci démontre que, l’estimation de la perte de glace lors des séismes glaciaires ne semble pas évidente à partir de leur magnitude. La comparaison des forces inversées et modélisées montre que nous sommes capables de reproduire les signaux sismiques et d’accéder ainsi à la dynamique du phénomène. Les informations contenues dans les variations temporelles de la force de vêlage permettent notamment d’inverser chaque paramètre individuel du modèle et d’estimer ainsi les dimensions et le volume de glace détaché / Glacial earthquakes have magnitudes Mw~5 and associated to the calving of large-scale (km3) unstable icebergs. In order to characterize the force at the origin of long-period seismic signals (10-100~s), we develop a source inversion scheme and a numerical modeling of iceberg capsize. Thanks to detailed analysis of the inverted force histories, we reveal the existence of several phenomena responsible for the seismic signal generation, being (1) an ice-avalanche triggered by the detachment of a first iceberg, (2) the calving and capsize of icebergs which apply a horizontal force normal to the glacial terminus, and (3) the ice-melange acceleration in the fjord. This shows that the interpretation to the event magnitudes is not straightforward as they represent the energy that is released by distinct mechanisms. With mechanical numerical modeling of the phenomenon, we show that the force amplitude does not linearly scales with the iceberg volume but also depends on various parameters that control capsize dynamics. This implies that the calving-induced mass loss cannot be estimated from the glacial earthquake magnitude only. Nevertheless, by comparing between seismic inverted forces and the modeling results, we are able to reproduce seismic signals and access the event dynamics. Informations that are contained in the force histories enable to invert each model parameter and thus estimate the iceberg dimensions and then volume

The consequences of complications during calving are currently costing the UK dairy cattle industry approximately £110 for a calving of moderate difficulty and £400 for one that is severe. With incidences of difficult first calvings reaching 24% and 4% for a moderate and severe difficult calving respectively, reducing calving complications would be of great benefit to the UK dairy cattle industry. This PhD evaluates (i) the importance, (ii) the most optimal way, and (iii) the potential consequences of genetically selecting for two main traits associated with calving complications, calving ease (CE) and stillbirth (SB). For this, approximately 50.000 first parity and 300.000 later parity national calving data records were kindly provided by two major milk recording organisations in the UK. The work carried out shows that detrimental effects following a difficult first calving are long-lasting as subsequent performance of both the dam and the calf involved is worsened. Fertility of the dam is negatively affected by a difficult calving resulting in an increased calving interval and decreased ability to conceive. A reduction in milk production of a veterinary assisted dam, compared to a non-assisted dam, was detected in the first part of lactation. Veterinary assisted born calves showed a significantly lower milk yield, compared to farmer assisted calves, throughout their first lactation as adult heifers suggesting that the physiological effects, or causes underlying a difficult birth, are long lived. The study advises that genetic parameters of calving traits are to be estimated with an extended sire multi-trait model (accuracy vs. practicality). On average, direct and maternal heritabilities for calving traits are low. A highly heritable indicator trait such as gestation length (GL) can aid in the estimation of genetic parameters for CE and SB although genetic correlations of these traits with GL are moderate. A significant negative genetic direct-maternal correlation was found for CE in first parity recommending farmers to consider both direct and maternal genetic merit for CE when making a selection decision. CE and SB are highly positively correlated traits. GL is maternally correlated to SB in first parity and directly to CE in later parities, both correlations are positive. Estimated genetic correlations with other important traits in dairy cattle breeding show that CE and GL are both directly and maternally related to important selection traits which need to be taken into account if implementation into breeding indices occurs. Results advise limiting the use of GL to benefit the prediction of parameters for low heritable calving traits rather than selecting on GL itself. Genetic correlations suggest that individuals born easily are genetically prone to high milk yield and have reduced fertility in first lactation. Difficult calving heifers are likely to be associated with being wide and deep and high producing animals with a reduced ability to subsequently conceive. Individuals that are born relatively early are associated with good genetic merit for milk production. And finally, individuals carrying their young longer are genetically associated with being wide and large animals that were born relatively early themselves. Lastly, an extension of the current univariate genomic model to a bivariate model, which allows for a possible genetic direct-maternal covariance, shows that improvement in accuracy of genomic breeding values can be gained from use of a bivariate genomic model for maternal traits such as CE. Further development of the model is however recommended prior to the publication of genomic proofs for CE or any other maternal trait. Genetic selection can serve as a tool in the reduction of difficult calvings. The results of this thesis serve to let this happen in a controlled and sustainable manner.

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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.

I apply a suite of seismic techniques to investigate iceberg calving at large glaciers around Greenland. Iceberg calving accounts for up to half of the Greenland Ice Sheet's annual mass loss, which makes understanding the physics of the calving process vital to gaining a clear picture of current behavior and future evolution of the Greenland Ice Sheet. However, the varied and complex modes of calving behavior at individual glaciers, paired with the challenges to data collection presented by an actively calving glacier, mean that much remains unknown about the dynamics of calving at marine-terminating glaciers. Seismic data offer a unique opportunity to study this active phenomenon, by allowing remote observation of calving events and quantification of the forces active during calving. Using seismic data collected during the most productive three years of buoyancy-driven calving on record, I estimate the forces active during iceberg calving at 13 glaciers around Greenland. My waveform-modeling results highlight the large number of buoyancy-driven calving events currently occurring at Jakobshavn Isbrae and other glaciers in west Greenland. I demonstrate that a glacier's grounded state exerts control on the production or cessation of rotational calving events and investigate the dynamics of calving at individual glaciers. I pair seismic results with terminus imagery to identify the location of individual calving events within calving sequences that occur over days to weeks at a single glacier terminus. By applying a new cross-correlation technique to seismic data collected within 100 km of three of Greenland's largest glaciers, I identify the occurrence of buoyancy-driven calving events with iceberg volumes up to two orders of magnitude smaller than previously observed. These small calving events frequently occur within ~30 minutes of a larger calving event. In between calving sequences, a glacier terminus changes little, suggesting that the majority of ice lost from marine-terminating glaciers occurs through these sequences. I estimate that these small events may contribute up to 30% more to dynamic mass loss than previously thought (up to 15 Gt/yr). I find no evidence of the cliff failure predicted by the marine-ice-cliff-instability hypothesis, in which catastrophic failure occurs when an ice cliff reaches a theoretical maximum-height limit, despite the three glaciers I investigate in detail having some of the tallest ice cliffs in the world. I use independent constraints on iceberg size from high-quality terminus imagery to present the first demonstration of an empirical relationship between glacial-earthquake magnitude and iceberg size. I investigate this relationship further by considering additional metrics of glacial-earthquake magnitude, and find advantages to using maximum force, rather than the more commonly employed mass-distance product Mcsf, as a measure of glacial-earthquake size. Through a detailed investigation into the character of the glacial-earthquake source, I identify key characteristics of the source function that generates the glacial-earthquake signal. I use experiments on both synthetic and observed waveforms to demonstrate that more-accurate estimates of glacial-earthquake size can be retrieved using source models constructed using a representation of the force history that is more sophisticated than that captured by the simple boxcar model. I confirm the presence of a correlation between iceberg volume and glacial-earthquake size, which moves us closer to having the ability to use remotely recorded seismic signals to quantify mass loss at Greenland glaciers. This work presents testable hypotheses for future model development.

Ultrasound-guided transvaginal follicular aspiration was used to obtain oocytes from cows to study follicular development and oocyte morphology. Follicular aspiration was conducted once during wk 1 to 12 postpartum on 120 lactating cows with 6 groups, separated by biweekly intervals. Approximately one half of the aspirated cows at each session were from the early groups (wk 1-2, 3-4, or 5-6) and the other half from the later groups (wk 7-8, 9-10, or 11-12). On the day of aspiration the number of follicles on each ovary, and their sizes, small (2-5 mm), medium (6-10 mm) and large (≥ 11 mm), were recorded. The collected oocytes were morphologically classified into 4 grades, with 4 = excellent, 3 = good, 2 = fair, and 1 = poor. Blood samples from the jugular vein and follicular fluid samples from the largest follicle were collected in order to perform hormone and metabolite assays. Environmental data were obtained from the local airport. There was a significant (P < .01) quadratic days pre- and postpartum by parity interaction for BCS. Body condition score for older cattle was the lowest at 90 d prior to calving and changed the least amount over time, while youngest cattle had the highest initial BCS at d 90 prior to calving and had the greatest change in BCS over time. Body condition score was the highest during summer calving season (3.3 ± .06) compared to BCS during winter calving season (2.6 ± .06). But the loss in BCS was greater for cows that calved in summer (-0.53 ± .06) compared to cows that calved in winter (-0.07 ± .08). Increased serum NEFA concentrations with simultaneous decreases in serum insulin concentrations for younger cattle implied a more negative EB status than for older cattle. The total number of follicles and total number of oocytes retrieved was significantly (P < .001) affected by a linear days postpartum by parity interaction with younger cattle having linear increases compared to decreases in the total number of follicles for older cattle. Oocyte quality score was affected by the quadratic days postpartum by parity interaction (P < .01) and calving season (P < .01). Younger cattle had higher initial quality scores compared to older cattle, but older cattle had higher quality oocytes towards the end of the 12 wk period compared with younger cattle. Younger cattle had higher E2 and IGF-I concentrations in follicular fluid associated with a higher number of total follicles and number of oocytes, compared to older cattle. However, oocyte quality of younger cattle seemed to be reduced and oocytes were less competent than for older cattle. Cattle in 3rd and greater lactation showed very little change in BCS and hormone and metabolite measures during early lactation, with no apparent decrease in oocyte quality, despite the aging effect on follicle numbers. This study demonstrated that conditions related to early lactation have a negative effect on oocyte quality and endocrine measures of dairy cattle and that animals of different ages are differentially affected. / Master of Science