An improved method for quantifying intake rate and ingestive behaviour of ruminants in diverse and variable habitats using direct observation

摘要

Using heterogeneous vegetation through grazing is a necessary component of de-intensification of livestock systems and conservation of natural environments. Better understanding of the dynamics of animal feeding behaviour is therefore needed, in particular in response to feed diversity and variability. On the basis of three on-farm experiments with ewes and goats, we improved a direct observation method that links intake behavioural response with variations in plant structure. This method makes it possible to continuously and closely monitor an individual animal's ingestive behaviour during the daily meals, by recording the mass and nutritive quality of its ingestive bites in situ and within its group. "Language" stemming from a coding grid for "bite categories" is proposed for real-time recording of all the bites taken from the full range of available plant parts. Bite categories are defined in order to be applicable to diverse and numerous plant species which allowed real-time recording in very diversified environments, while the impact of grazing alters the plant structure. The continuous presence of an observer does not appear to disturb the animals being monitored, since the variations of their total daily intake time and their diet quality are close to the ones of the groups. The dynamics of ingestive behaviour is explored at different time scales: daily intakes, meal kinetics and biting process. Daily intakes were similar for dry ewes grazing swards invaded by shrubs (77.9 +/- 10.2 and 75.1 +/- 16.9 g DM/kg LW0.75). They were much higher for lactating goats browsing within a shrub encroached oak coppice (125.8 +/- 7.5 g DM/kg LW0.75). Cumulative meal kinetics were quite regular and their slopes are of descending form. Our method allowed characterising the huge diversity of bite types that compose such a regular meal. Bite mass ranged between 0.01 and 1.72 g DM. Instantaneous DM intake rate and instantaneous quality of intake were highly variable (i.e. about 20% of variation in OM digestibility during a single meal). At the scale of biting, our method allows to explore the effect of plant structure alteration on the ingestive response and the resulting intake rate. We confirm that intake rate is more influenced by the mass than by the frequency of bites. The main advantage of this method lies in its capacity to characterise bite intake dynamics in very diversified vegetation, from the very short term, i.e. the meal components, to the long term, i.e. several days in a paddock.