Assessing the welfare of laboratory-housed marmosets (Callithrix jacchus): Effects of breeding and infant rearing background

Abstract

The common marmoset is the most frequently used New World primate in laboratory research and testing. In the UK, their use is strictly controlled by the Animals (Scientific Procedures) Act, which is underpinned by the principles of humane science: Replacement, Reduction and Refinement. Despite their use, there are a number of problems associated with the breeding of marmosets, including low dam longevity and increasing litter sizes. Large litters have led to high infant mortality and the need for human intervention to improve infant survival, which involves removal from the family for substantial periods of time. Previous research in a range of primate species shows that early life family separation is associated with numerous adverse behavioural and physiological effects. This project therefore sought to systematically investigate the effects of breeding and infant rearing practices, integrating a number of measures to assess the welfare of laboratory- housed marmosets. Potential predictors of dam longevity and litter size were first identified in three captive UK colonies, over four decades. Dam longevity was found to be approximately 6 years, with heavier dams living longer, but overall there was no consistent improvement in longevity over the decades. As longevity varied widely between colonies and over time, environment may be one of the most important factors. Approximately half of all births at each colony were litters larger than two, and these larger litters had greater infant mortality. Only dam weight at conception was useful in predicting litter size, with heavier dams producing larger litters. The consequences of large litters and early separation from the family for supplementary feeding were then investigated. Although twins had lower body weight than 2stays (two infants remaining with the family after death of the other littermate/s) and supplementary fed triplets, they also had the fewest health problems. There was also some evidence that animals from larger litters were more at risk of suffering from extreme low weight. Some minor differences were found in behavioural development between litter sizes. Singleton infants received more rejective rearing, while 2stays received more protective rearing, perhaps following the loss of an infant. While twin infants gained independence earlier than singletons or 2stays, they did not appear to cope better with stress in adulthood, displaying more significant increases in stress-related behaviour following the routine stressor of capture and weighing, compared to 2stays and supplementary fed triplets. While overall cortisol unexpectedly decreased from baseline to post capture, there were only significant fluctuations in 2stay marmosets. Instead, there were some increases in positive behaviour in supplementary fed triplets following the stressor, suggesting enhanced coping ability. However, in another group of supplementary fed triplets, there were subtle increases in depressive-like symptoms, measured using cognitive bias and preference tests, suggesting a reduced expectation of and interest in rewards. There were however no differences between family-reared and supplementary fed marmosets in time to learn a visual discrimination task, or in responses to temperament tests. Therefore, while it was hypothesised that early family separation would have adverse developmental consequences, there were actually very little differences between marmosets of different litter sizes and rearing backgrounds, across the range of measures. Results suggest that the current supplementary feeding programme, along with a regular human socialisation programme, minimises any potential negative effects. However, we should always be finding ways to improve the lives of animals in our care. Possible Refinements include reducing dam weight to increase twin births and improve infant survival, and training to allow supplementary feeding on the carrier’s back, to prevent infant separation and reduce disruption to the family. These Refinements could reduce fear and allow monkeys to become more resilient to the laboratory environment.