Author(s): Laura E. Webb 1,*, Margit Bak Jensen 2, Bas Engel 3, Cornelis G. van Reenen 4, Walter J. J. Gerrits 5, Imke J. M. de Boer 1, Eddie A. M. Bokkers 1
Foraging animals gather information about available resources at the expense of optimising immediate rate of energy gain , . Ruminants have been found to trade-off between optimising rate of energy gain and minimising disadvantages to rumen function caused by the intake of high energy food, by including in their diets roughage high in fibre and low in energy , . This requires prior association between the sensory characteristics of feed and their post-ingestive consequences . Ruminants spend extensive time feeding and ruminating. Mastication and rumination promote salivation, an important buffering agent in the rumen, and reduce feed particle size to enable passage of feed into the abomasum , . As a consequence, ruminants have a high incentive to chew and ruminate , , and they may sometimes show a preference for roughages that require long chewing times . The latter is especially relevant in farmed ruminants fed high energy diets with little fibre, as these animals develop abnormal oral behaviours due to limited opportunity to chew and ruminate -. Abnormal behaviours occur in sub-optimal environments and are a sign of poor welfare in captive animals .
A method for investigating foraging behaviour in ruminants is to quantify the preferences for two simultaneously available feeds. Manipulating the particle length of roughage is an easy way to control the rate of energy gain, without affecting taste and smell. Compared to longer ones, smaller particles of roughage are ingested at a higher rate -, and pass faster/more easily through the reticulorumen , resulting in an increased rate of energy gain. However, feeding only small amounts of small particles of roughage, as opposed to longer roughage particles, on top of a high concentrate diet, may lower ruminal pH in the long term, increasing the chances of developing acidosis . These diets may also lead to ruminal plaque formation, i.e. a sticky mass of hairs and small feed particles between the papillae , and ruminal hairball development . In addition, small roughage particles often mean less chewing and rumination than longer particles. Less chewing and rumination increases energy intake rate by decreasing ingestion and digestion effort, but these behaviours also stimulate saliva secretion, which is an important buffering agent in the rumen . Ruminants were capable of making foraging choices that favour good rumen function by selecting a large portion of chopped roughage particles (30%) in their total diet, when chopped and ground roughages were offered together , . In previous studies, however, animals had to balance energy intake and good rumen function, because no other feed was provided besides roughage. If energy intake was taken out of the equation, by, for example, feeding high energy concentrate, ruminants are expected to prefer longer particles of roughage, as the need for good rumen function would then become more important than rate of...