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The ChAdOx1 nCoV-19 vaccine has been associated with increased risk of thrombosis. Understanding of management of these rare events is evolving, and currently recommended treatments include human normal immunoglobulin and non-heparin anticoagulation such as direct oral anticoagulants. Our report describes three consecutive patients presenting to a London teaching hospital with vaccine induced thrombotic thrombocytopenia (VITT), also referred to as vaccine-induced prothrombotic immune thrombocytopenia (VIPIT). The patients ranged in age from 40-54 years and two had no known previous medical comorbidities. Two patients had cerebral venous sinus thrombosis and one had a deep vein thrombosis. Two were treated with anticoagulation; one with oral rivaroxaban; and the other with an intravenous argotraban infusion that was later converted to oral apixaban. One patient received three doses of human normal immunoglobulin and five days of therapeutic plasma exchange. This case series may be used to improve understanding of the clinical course and management of VITT.

For animals moving together in groups, navigating collectively requires group members to reach consensus decisions about, among other things, the direction in which to travel. This thesis focuses on how consensus collective decisions are made when certain individuals have a disproportionate influence on the group’s movement decisions. The specific focus is on hierarchical decision-making during collective movement, whereby an individual's position in the hierarchy corresponds to its relative contribution to the directional decision-making process. I used two model species, homing pigeons (Columba livia) and the Characin fish (Astyanax mexicanus) to explore the mechanisms and consequences of leadership hierarchies, using a combination of GPS tracking and high-resolution video recording. Across several experiments, the following key results emerged: Previous navigational experience contributes to structuring navigational leadership hierarchies in homing pigeons, but only at the most influential positions. Birds with local experience occupy the top hierarchical positions significantly more often than inexperienced birds. This suggests there is an advantage to individuals in having an experienced leader when homing as a group. When leader birds hold highly inaccurate information, leadership hierarchies are spontaneously rearranged causing the original leaders to lose influence over flocks. This demonstrates the importance flexibility in decision-making structures, which may thus prevent the propagation of navigational errors – detrimental to all individuals within the flock – through the hierarchy. Homing pigeon navigational leadership hierarchies can be stable over long periods of time, but only in flocks with high levels of inter-individual variation in age and experience. Flocks homogeneous in age and experience showed no hierarchy stability. This highlights the importance of flock composition in determining the stability of navigational leadership hierarchies, which potentially impacts on the advantages of these decision-making structures. Three-dimensional data are not a necessary requirement for identifying leadership hierarchies in animals that move and interact in three dimensions. A two-dimensional directional correlation delay model was able to correctly identify leader-follower interactions in three-dimensional shoals of Astyanax mexicanus. Overall, this thesis has shed light on the mechanisms of consensus decision-making, involving hierarchies of influence, during group movement. Through this knowledge we can further our understanding of the adaptive significance of collective behaviour.

Poor nutrition is a major factor limiting the productivity of small ruminants in St. Kitts and Nevis as well as in the wider Caribbean region. Inadequate quantity and quality of natural pastures during the dry season is a major constraint limiting the local supply of sheep and goat meat. The objectives of this study were the establishment of droughttolerant, high-yielding crops capable of good quality forage that could also be preserved as silage for year-round feeding of small ruminants. Two hectares of Mulato II grass (Brachiaria hybrid CIAT 36087) were planted in the dry season during February 2012, with a re-seeded section during April 2012. Forage yield after 12 weeks of successful establishment was 4,783 kg of dry matter (DM) per ha. In July the Mulato grass was harvested and conserved as silage in 153 plastic bags of 20 kg and 550 silage bags of 11 kg, for a total yield of 10,317 kg fresh ensiled material per ha. During the wet season after 3.5 weeks of re-growth, the Mulato grass produced 10,465 kg DM/ha, 2.2 times more forage compared to the dry season. For the forage sorghum (Sorghum bicolor), two cycles of Great Scott brown mid-rib were established and harvested: one in the dry season and the other in the wet season, March to May 2012 and November to January 2013, respectively. During the dry season the forage sorghum produced 1,870 kg DM/ ha with 81-day of growth, whereas in the rainy season, the forage sorghum produced 1.8 times higher, 3,429 kg DM/ha, with 53-day of growth. Successful establishment in the dry season and forage production during both the dry and wet season proved that Mulato grass and forage sorghum are valid forage options for small ruminant production under the Caribbean weather conditions, with the potential to increase farmers' income and provide year-round meat protein sources for these communities.