The influence of different boundary conditions on the response of the head to impact: a two-dimensional finite element study.

The objective of the present study is to gain a better understanding of the possible importance of skull-brain interface conditions, boundary conditions at the head-neck junction, and brain material properties when modeling the response of the human head to transient loadings. To that end, a two-dimensional plane strain finite element model of a para-sagittal section of a human head has been developed. The model comprises the brain and the skull, with the foramen magnum represented by a force-free opening. The model geometry was obtained from MRI data. The material properties used were adopted from the literature and are homogeneous and isotropic. In all analyses the skull bone was modeled as a linearly elastic material. First, to enable a comparison between simulation results and experiments reported in the literature, the loading conditions, realized in experiments reported in literature, were used as input to the completely linearly elastic model without a kinematic constraint at the head-neck junction. This was done for both rigid coupling and no coupling at the skull-brain interface. Next, various versions of the model were constructed by using different combinations of the following features: linear elastic or viscoelastic brain material properties, different contact conditions at the skull-brain interface, and incorporation of a neck constraint. The results show that both coup and contrecoup pressures are much more sensitive to the type of skull-brain interface condition than to the presence or absence of a force-free foramen magnum. A neck constraint proves to be an important modeling assumption, because of its effect upon the deformation of the brain. The use of different time-dependent deviatoric material parameters for the brain did not significantly change the head's response.

Individual behavioural characteristics in pigs--influences of group composition but no differences in cortisol responses.

To determine the effect of group composition on backtest (Bt) responses and to determine the predictive value of the Bt for the physiological stress response to weaning and mixing, 814 pigs were backtested at 3, 10 and 17 days of age. Twenty-nine percent of all pigs were cross-fostered at 3 days according to Bt responses and groups were formed of animals with high responses (HR) only, low responses (LR) only or mixed groups of animals with high, intermediate and low responses (MISC). Original litters (OR, no cross-fostering) were used as controls. Cortisol responses were measured in saliva after weaning at 4 weeks of age and after moving and mixing at 9 weeks of age. In HR groups, mean Bt responses decreased after cross-fostering while in LR groups, mean Bt scores increased. In both groups, Bt responses of individual animals before and after cross-fostering were not correlated. In MISC and OR groups, all Bt scores were correlated. Weaning and mixing caused a significant rise in cortisol in all animals while moving or weighing did not. No relations were found between Bt scores and cortisol levels. We conclude that Bt behaviour can change according to the social environment between 3 and 10 days. This could be intentional, to form a varied group, or it might be caused by a change in the hypothalamic-pituitary-adrenal (HPA) function due to social stress. At an older age, this ability is lost and common farm practises such as regrouping, weaning and mixing of piglets at ages >10 days might have a negative effect on the piglets.

A note on the influence of starting position, time of testing and test order on the backtest in pigs.

The backtest determines the coping behaviour of a piglet in a standardised stress situation, which might be a measure for the coping style of that animal. Backtest results are related to other parameters such as immune responses and production. In this study, the backtest was standardised and it was studied if time of testing or the order in which animals were tested influenced backtest results. One hundred and eight-four piglets from 18 sows were tested at 3, 10 and 17 days of age. Before testing, the sow was disturbed to ensure that all piglets were awake. This standardisation of the starting position before testing did not improve the correlations between backtest results in the successive tests. No relations were found between backtest results and time of testing or test order.

[Comparison of the efficacy of two different iron supplements for anemia prevention in piglets]. / Vergelijkend onderzoek naar de werkzaamheid van twee verschillende ijzersupplementen voor anemiepreventie in biggen.

In a randomized, confirmatory study performed between July and October 2000 the efficacy of two iron products in preventing iron deficiency anaemia was compared. A total of 102 newborn piglets from ten litters were treated intramuscularly with 200 mg iron as iron dextran per ml, or 200 mg iron as gleptoferron per ml. For true comparison, piglets within a litter of a sow were subdivided into pairs on the basis of birth weight (one pair of the two heaviest piglets, et cetera). Within a pair, treatment with the iron supplements was randomly allocated. One group of piglets was injected at an age of 1 day (experiment 1) and the other group of piglets was injected at an age of 3 days (experiment 2). The piglets were weighed and blood samples were taken at an age of 18 days (experiment 1) or at an age of 19 days (experiment 2). Average daily weight gain and haemoglobin concentrations of both treatment groups were compared. Both products were very effective in preventing anaemia. No significant differences could be found between the two formulations. It can be concluded that iron-dextran and gleptoferron can be used with similar effect for anaemia prevention in piglets.

[Individual behavioral characteristics of pigs and their impact on production]. / Individuele gedragskarakteristieken van varkens en de relatie met productieresultaten.

Two studies were carried out with pigs to determine the relationship between back test results and production parameters and between back test results and other factors. In the first study, 823 piglets were tested with the back test at 10 and 17 days of age. Production parameters such as average daily weight gain and lean meat percentage were determined. In the second study, the back test was performed on 566 piglets at 3, 10, and 17 days of age. The number of escape attempts in the back test (back test score) of the mother was known for 364 piglets. Parameters concerning the health of the sow and piglets were recorded, as well as the sow's reaction to piglet removal for testing. The relationships between production parameters and back test scores of the animals were calculated, as well as the influence of birth weight, sex (all males were castrated), parents, and health parameters on back test scores. Back test scores were fairly consistent over successive tests for each piglet. Males had higher back test scores than females, and piglets from sows with low back test scores also had low scores. Finally, a higher back test score was correlated with a higher lean meat percentage and a better carcass grading at slaughter; no relation with daily weight gain was found. It is concluded that there are individual differences in the way pigs cope with a stressful situation, as measured with the back test, and that this coping behaviour is consistent. A positive correlation exists between back test scores at a young age and lean meat percentage at slaughter. The response to stress, and hence back test scores, is assumed to be inheritable.