The effect of rumen adaptation to oxalic acid on selection of oxalic-acid-rich plants by goats

Rumen microbial degradation is an important route for detoxification of sec ondary plant compounds encountered in the diets of free-grazing ruminants. Exposure to diets containing particular secondary plant compounds can lead to increased rates of secondary compound degradation in the rumen. An exper iment was conducted to determine whether rumen adaptation to oxalic acid wo uld influence the diet selection of gears offered choices between plant spe cies differing in their oxalic acid content. Twelve adult female goats were divided into two groups of six animals each. One group received a daily or al dose, in gelatin capsules, of 0.6 mmol oxalic acid/kg live weight per d throughout the experiment while the other group received placebos consistin g of empty gelatin capsules. After an adaptation period of 8d, the animals were allowed to graze a mixture of spinach (rich in oxalic acid) and cabbag e (low in oxalic acid) for 7 hid on two consecutive days per week during fo ur consecutive 1-week periods. Intervening days were spent on grass pasture . Diet composition and intake were measured using cuticular wax n-alkanes a s internal markers. Results showed that adapted goats included a higher pro portion of spinach in their diet (P < 0.05) although absolute intakes of sp inach were the same for the two groups. Goats in the oxalic-acid-adapted gr oup consumed less cabbage than control animals (P < 0.05) suggesting that a daptation to oxalic acid at the rumen level may have interfered with detoxi fication of cabbage-derived secondary plant compounds. Voluntary intake inc reased progressively through the four experimental periods (P < 0.001) with a tendency for higher intakes among control than among adapted animals (P < 0.1). The experiment demonstrates how differences in the rate of degradat ion of secondary plant compounds may influence diet selection in ruminants.