Reviewing factors affecting neonatal health and survival in farm animals
The animal Article of the Month for November is entitled ‘Prenatal stress, immunity and neonatal health in farm animal species’
In farm mammals, preweaning mortality rates are high and variable between farms: 10-25% in lambs, 7-50% in kids, 0-50% in calves, 0-35% in foals, 5-35% in pigs. The major causes of mortality and health problems are hypothermia, hypoxia or starvation of weak neonates. Maternal undernutrition, mismothering, injury and infection are also other significant causes of morbidity and mortality after the perinatal phase. Important efforts are performed by farmers to reduce these economically and ethically questionable losses. Concurrently, gestating females are often exposed to stressors or poor housing conditions that also question modern industrial farming acceptability. For example, climatic stress, being moved into a new housing environment, handling and fear from human, hunger due to food limitation, leg disorders and social stress due to grouping with unfamiliar conspecifics are common stressors. When occurring during early gestation, these events might lead to abortions or to partial foetal losses in species giving birth to large litters. Most of the time, however, the development of the foetuses continues until term. Studies in rodent and primates show that maternal stress during gestation influences the developing foetus, and can be a risk factor for health disorders later in life, during infancy as well as adulthood.
In farm animals, accurate data investigating whether prenatal stress impairs neonatal mortality and morbidity are lacking. On one hand, most of the studies conclude negatively about an influence on birth weight, neonatal mortality and morbidity but these studies are based on too small numbers of experimental animals to be accurate. On the other hand, experimental studies suggest that prenatal stress might impact important factors involved in the preservation of neonatal health. These factors can be either related to maternal biology or to long-term alterations in foetal ontogeny. This article is a review of the literature that summarizes the knowledge about these two aspects.
In pigs and ruminants, maternal stress alters the transfer of passive immunity from the mother to the newborn, by decreasing the quantity and quality of the colostrum produced by the mother and reducing the absorption of colostral IgG through the gut of the neonate. Maternal stress can sometimes alter other important maternal parameters of neonatal survival such as maternal care to the newborn, and maternal immune function and health, which can influence the transfer of pathogens from the mother to her foetus or neonate. At the level of the offspring, prenatal stress can also alter immune defenses during the first weeks of life such as the inflammatory response and lymphocyte functions. Cortisol and reproductive hormones controlling colostrogenesis are pointed out as possible hormonal mediators.
In conclusion, even if maternal stress is shown to alter important parameters related to neonatal survival in farm animals, field data and epidemiological studies are still needed to quantify the role of maternal welfare problems in neonatal health and survival.
Authors: E. Merlot, H. Quesnel and A. Prunier
The animal Article of the Month is selected by the Editor-in-Chief and is freely available for one month