The Welfare Impact of Increased Gavaging Doses in Rats

Abstract

AbstractTextbook recommendations for gavaging rats vary between 1-5 ml for an adult rat. Rats weighing either 130 g or 250 g were gavaged with varying dosages of barium sulphate (BaSO4). After dosing, radiographs were taken at 0, 15 and 60 min. Animals showing a section of the small intestine totally filled with BaSO4 were scored as displaying spontaneous release. Other rats of the same sizes were gavaged with similar doses and subsequently tested in an open-field arena for behavioural abnormalities that might indicate stress or pain resulting from the procedure. Body temperature before and after treatment was recorded using microchip transponders. None of the 250 g rats in the 1 ml dosage group showed spontaneous release through the pyloric sphincter. In the 2 ml and 4 ml dosage groups, only one out of five animals showed spontaneous release. In the 6 ml dosage group, half of the animals showed spontaneous release. In the 8 ml and 10 ml dosage groups, five out of six and four out of five, respectively, showed spontaneous release. If doses were higher than 12 ml, no animal was able to keep all of the BaSO4 in its stomach. In the rats weighing 130 g, the 3 ml dosage group showed only one out of four rats with spontaneous release, whereas in the 5 ml and 7 ml dosage groups, all animals showed spontaneous release. After 15 min, all of the rats in both weight groups showed BaSO4 in the duodenum. Ambulation, rearing up onto the hind legs and defecation, as well as body temperature immediately after dosing, correlated very strongly with the dose (ml kg−1); increasing the dose resulted in reduced ambulation, rearing, defecation and body temperature. However, 10 min after performance of the open-field test, neither body temperature, serum corticosterone nor serum glucose showed any correlation with dose. This study indicates that high doses (ie doses up to 10 ml for a 250 g rat) might be safe to use; however, if an adverse impact on the rat is to be avoided, use of much lower doses should be considered—for example, doses that do not enforce opening of the pyloric sphincter in any rat. This would be less than 4 ml kg−1 in a 250 g rat.