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Southern right whales (Eubalaena australis) are mysticete cetaceans commonly observed in the coastal waters of Brazil, particularly in Santa Catarina State. There is limited understanding of the causes of calf mortality in this species, particularly concerning infectious diseases. We report a case of omphalophlebitis caused by Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) that led to septicemia in a Southern right whale calf. Gross examination revealed an incompletely healed umbilicus with fibrin deposition and amorphous yellow material present in the lumen of the umbilical vein on the cut surface. The main histopathological findings showed fibrinosuppurative omphalophlebitis with numerous coccoid basophilic bacterial aggregates. These aggregates were also observed in the lamina propria, submucosa, and muscular layers of the small intestine and uterus, as well as in the interstitium of the kidneys and within blood vessels of the skin, skeletal muscle, heart, and ovaries. Tissue samples taken from the umbilicus and uterus were inoculated on 5% sheep blood agar and MacConkey agar. Small, transparent colonies that exhibited complete hemolysis were identified on blood agar. Gram staining revealed the presence of Gram-positive cocci arranged in chains. The bacterial isolate was analyzed using the MALDI-TOF technique, which confirmed its identity as S. zooepidemicus. The presence of S. equi antigen in the extra-umbilical aggregates was confirmed through immunohistochemistry. These findings underscore the significance of streptococcal infections in cetaceans and contribute valuable data regarding calf mortality in baleen whales. Furthermore, we provide new insights into the understanding of marine ecosystem health markers., Competing Interests: Declarations. Ethics approval: This article agrees with the content of the Brazilian resolutions of the National Council for Control of Animal Experimentation– CONCEA where it involves animals. The authors assume full responsibility for the presented data and are available for possible questions should they be required by the competent authorities. This study was approved by the Comissão de Pesquisa of the Universidade Federal do Rio Grande do Sul (COMPESQ/UFRGS) (number 46630). Sistema Nacional de Gestão do Patrimônio Genético e do Conhecimento Tradicional Associado (SisGen) registration number: A37FC83. Competing interests: The authors declare no competing interests., (© 2025. The Author(s), under exclusive licence to Springer Nature B.V.)

Improving our understanding of energy allocation in reproduction is key for accurately parameterizing bioenergetic models to assess population responses to environmental perturbations and anthropogenic disturbance. We quantified the energetic cost of gestation in humpback whales (Megaptera novaeangliae) using historical whaling records, non-invasive unoccupied aerial system (UAS) photogrammetry and post mortem tissue samples. First, we estimated relative birth size using body length measurements of 678 mother-fetus pairs from historical whaling records and 987 mother-calf pairs measured in situ using UAS-photogrammetry. The total energetic cost of gestation includes fetal growth (FG), heat increment of gestation and placental tissue development. FG was modelled from conception to birth, with fetal volume and mass estimated using the volume-to-length relationship of perinatal calves and published humpback whale tissue composition estimates. Tissue-specific energy content was quantified using post mortem bone, muscle, viscera and blubber samples from a neonatal humpback whale. Placental tissue development was estimated using humpback whale placental tissue and published equations. Relative birth length was found to be 33.75% (95% CI: 32.10-34.61) of maternal length. FG rates and absolute birth size increased with maternal length, with exponential growth in fetal length, volume and mass resulting in minimal energetic costs over the first two quadmesters (0.01-1.08%) before increasing significantly in the final quadmester (98.92%). Gestational heat constituted the greatest energetic cost (90.42-94.95%), followed by fetal (4.58-7.76%) and placental (0.37-1.83%) tissue growth. Our findings highlight the energetic costs endured by capital breeding females preceding parturition, with the most substantial energetic costs of gestation coinciding with migration and fasting. KEY POINTS: We quantified the energetic cost of gestation using body length measurements of mother-fetus pairs from historical whaling records, length estimates of mother-calf pairs measured in situ using aerial photogrammetry and post mortem tissue samples. Fetal growth rates and birth size increased with maternal length, with fetal length, volume and mass increasing exponentially over gestation. Energetic costs over the first two quadmesters were negligible (0.01-1.08%) before increasing significantly in the final quadmester (98.92%). Though larger females incur nearly twice the energetic cost of smaller females, they are likely buffered by greater absolute energy reserves, suggesting smaller females may be less resilient to perturbations in energy balance. We demonstrate the significant energetic costs incurred by pregnant humpback whales, with most of the energetic expenditure occurring over the final 100 days of gestation. Late-pregnant females are, therefore, particularly vulnerable to disruptions in energy balance, given periods of greatest energetic stress coincide with fasting and migration., (© 2024 The Authors. The Journal of Physiology © 2024 The Physiological Society.)