Seasonal regulation of condensed tannin consumption by free-ranging goats in a semi-arid savanna

Abstract

Although condensed tannins (CTs) are known to reduce forage intake by mammalian herbivores in controlled experiments, few studies have tested these effects in the field. Thus the role of CTs on foraging ecology of free-ranging herbivores is inadequately understood. To investigate the effects of CTs under natural savanna conditions, we pre-dosed groups of goats with polyethylene glycol (PEG, a CT-neutralising chemical), CT powder or water before observing their foraging behaviour. While accounting for the effects of season and time of the day, we tested the hypothesis that herbivores forage in ways that reduce the intake rate (g DM per minute) of CTs. We expected pre-dosing goats with CTs to reduce CT intake rates by (1) consuming diets low in CTs, (2) reducing bite rates, (3) increasing the number of foraging bouts, or (4) reducing the length of foraging bouts. Lastly, (5) expected CT to have no influence the number of dietary forage species. In both wet and dry seasons, pre-dosing goats with CTs resulted in lower CT consumption rates compared to PEG goats which seemed relieved from the stress associated with CT consumption. During dry season, the number of dietary forage species was similar across treatments, although goats that were dosed with PEG significantly increased this number in the wet season. Dosing goats with PEG increased the number and length of browsing bouts compared to goats from the other treatments. Pre-loading goats with PEG also tended to increase bite rates on browse forages, which contributed to increased consumption rates of CTs. Based on the behavioural adjustments made by goats in this study and within the constraints imposed by chemical complexity in savanna systems, we concluded that herbivores under natural conditions foraged in ways that minimised CTs consumption. More research should further elucidate the mechanism through which CTs regulated feeding behaviour.

Rumen function in goats, an example of adaptive capacity

“…This ability can be linked to a behavioural adaptation towards some secondary metabolites. It may lead to modifications of the dietary selection pattern (Duncan et al ., 2000; Mkhize et al ., 2018), but also to specific detoxification enzymatic batteries of secondary metabolites which can be realised at different places in ruminants but mainly in the epithelium of the rumen. In the case of rhodanese, a ubiquitous enzyme playing a central role in cyanide detoxification, the activity was highest in the epithelium of the rumen of goats (Nazifi et al ., 2003).…”

Effect of Tannin-rich Mimosa pigra Leaf Meal in Molasses-based Blocks on Feed Intake, Rumen Parameters, and Blood Metabolites of Dairy Heifers

“…Therefore, ammonia nitrogen to be absorbed across the rumen wall into the portal vein to process the urea cycle is the limit. Feeding with tanniniferous supplements is generally a decrease in blood urea nitrogen (Mkhize et al, 2018;Zhang et al, 2019) in response to the formation of nitrogen complexes condensed tannin in the rumen and enhancing protected protein supply into the small intestine (Min and Hart 2003). Although high in inorganic contents of MBB, no sign of impaired kidney function was detected in response to total protein and creatinine levels.…”

Effects of dietary replacement of broiler litter withMucuna pruriens utilisforage and seed meal on performance, carcass characteristics, blood biochemical and physiological parameters in indigenous goats

“…However, even goats under free-range conditions will reduce intake of tannin-rich feed in order to regulate the amount of tannins in their digestive systems. In this regard, they regulate their foraging behaviour by changing the number and lengths of browsing and grazing bouts in ways that minimise condensed tannin consumption [89].…”