Eric Nævdal

Maternal investment, sibling competition, and offspring survival with increasing litter size and parity in pigs (Sus scrofa)

The aim of this study was to examine the effects of litter size and parity on sibling competition, piglet survival, and weight gain. It was predicted that competition for teats would increase with increasing litter size, resulting in a higher mortality due to maternal infanticide (i.e., crushing) and starvation, thus keeping the number of surviving piglets constant. We predicted negative effects on weight gain with increasing litter size. Based on maternal investment theory, we also predicted that piglet mortality would be higher for litters born late in a sows life and thus that the number of surviving piglets would be higher in early litters. As predicted, piglet mortality increased with increasing litter size both due to an increased proportion of crushed piglets, where most of them failed in the teat competition, and due to starvation caused by increased sibling competition, resulting in a constant number of survivors. Piglet weight at day 1 and growth until weaning also declined with increasing litter size. Sows in parity four had higher piglet mortality due to starvation, but the number of surviving piglets was not affected by parity. In conclusion, piglet mortality caused by maternal crushing of piglets, many of which had no teat success, and starvation caused by sibling competition, increased with increasing litter size for most sow parities. The constant number of surviving piglets at the time of weaning suggests that 10 to 11 piglets could be close to the upper limit that the domestic sow is capable of taking care of.

FIGHTING TRANSIENT EPIDEMICS—OPTIMAL VACCINATION SCHEDULES BEFORE AND AFTER AN OUTBREAK

Epidemic diseases afflict all countries, and all epidemics are costly to society. The present paper examines optimal vaccination trajectories before and after an outbreak of a special class of epidemics where the disease normally eradicates itself. The focus is on epidemics where mortality may be ignored, influenza being the prime example. One important insight is that there may be increasing returns to scale in vaccination.

Optimal screening for genetic diseases

Screening for genetic diseases is performed in many regions and/or ethnic groups where there is a high prevalence of possibly malign genes. The propagation of such genes can be considered a dynamic externality. Given that many of these diseases are untreatable and give rise to truly tragic outcomes, they are a source of societal concern, and the screening process should perhaps be regulated. This paper incorporates a standard model of genetic propagation into an economic model of dynamic management to derive cost benefit rules for optimal screening. The highly non-linear nature of genetic dynamics gives rise to perhaps surprising results that include discontinuous controls and threshold effects. One insight is that any screening program that is in place for any amount of time should screen all individuals in a target population. The incorporation of genetic models may prove to be useful to several emerging fields in economics such as genoeconomics, neuroeconomics and paleoeconomics.