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Two experiments were conducted to investigate the effect of ruminal infusion of volatile fatty acids (VFAs) on eating and rumination behaviour and feed utilization in sheep fed on hay. The amounts infused were 300,300 and 150 kcal per day per animal of acetic, propionic and butyric acids, respectively. Each acid solution was continuously infused into the rumen of sheep fed on timothy hay alone (Experiment I). In Experiment II, sheep fed on roughage with varied crude protein (CP) levels (6.0, 7.3, 9.1 and 15.5% DM). Four sheep, two in each, were used in repeated crossover designed experiments. Daily eating time was lengthened by infusion of acetic and propionic acids as compared to control. There was no change in eating time after infusion of butyric acid (Experiment I). Daily eating time increased after propionic acid infusion and change in CP contents of the basal diet compared to control sheep. There was no change in eating time after infusion of acetic acid (Experiment II). Rumination appearance tended to shorten after infusion of acetic and propionic acids as compared to that of control. Butyric acid infusion gave opposite (Experiment I). Rumination appearance was long with an increase in dietary CP, but was not changed by ruminal infusion of volatile fatty acids (Experiment II). Daily rumination time tended to be long after infusion of butyric acid and short after infusion of acetic acid, and did not change after infusion of propionic acid (Experiment I). Cyclic rate tended to lengthen after infusion of acetic acid as compared to that of control, but there was no change after infusion of propionic and butyric acids (Experiment I). Cyclic rate was shortened after infusion 1 Corresponding author 2 Present address: Department of Animal Science and Production, Sokoine University of Agriculture, P.O. Box 3004, Chuo Kikuu, Morogoro, Tanzania 92 C„ C, AND C, ACID INFUSION AND RUMINATION BEHAVIOUR 2 ' 3 4 of acetic acid regardless of the CP content in the diet compared to that of control. Ruminal infusion of propionic acid had no clear effect on cyclic rate in sheep fed on diets with varied CP contents (Experiment II). Rumination appearance was fairly changed with varying levels dietary CP content regardless ruminal VFAs infusion. It was therefore, concluded that ruminal infusion of VFAs had little effect on eating and rumination behaviour and feed utilization. It was further concluded that chemical stimulus rather than physical stimuli, such as the increment of ruminal nitrogen could influence the chemoreceptor on the rumen wall. KEY WAORD: eating behaviour, rumen, rumination, VFAs infusion, sheep, feed utilization INTRODUCTION Rumination behaviour contributes to the increase in utilization of roughage feeds through particle size reduction, which facilitates their degradation in the rumen. Particle size reduction through re-mastication of the feed improves rumen microbial and fermentation activities (Welch and Smith, 1969). Rumination behaviour is closely related to the amount of feed ingested (Gordon, 1965; Fujihara et al., 1990b) and is influenced by changes in physical properties and/or chemical composition of feed ingested (Gordon, 1958; Fujihara, 1980; Fujihara and Nakao, 1990a; Mawuenyegah et al., 1997). Rumination is initiated by the presence of ruminal ingesta by chemical and/or physical stimuli to receptors in the rumen wall (Fujihara et al., 1989). However, the exact mechanism involved is not clearly known (Fujihara and Nakao, 1990b). Rumination index (time spent ruminating per 100 g DM intake), which also defines rumination efficiency, is highly influenced by the chemical and physical quality of the feed (Dryden et al., 1995). The products of rumen fermentation (VFAs) and the extent of ruminal fermentation are closely related to rumination behaviour. Infusion of acetic acid into the rumen alone has no significant effect on rumination behaviour in sheep fed on low quality hay. The type and form of forage eaten and significantly the amount of crude protein fed seem to also play a great role (Fujihara et al., 2002b). Increasing protein (Fujihara and Nakao, 1984) and energy supply (Weston, 1996; Mawuenyegah et al., 1997) to the rumen helps in maintenance of optimal rumen condition from microbial growth and fibre digestion resulting in higher voluntary intake. The objectives of this study were to investigate the effect of infusing VFAs alone on the eating, rumination behaviour and feed utilization on sheep fed on hay diets (Experiment I). The effect of ruminal infusion of acetic and propionic acids with varied CP levels in the form of urea on eating, rumination behaviour and feed utilization in sheep fed on grass hay diets was also investigated (Experiment II). Fujihara et al. (1990a) have briefly described part of this work. FUJIHARA T. ET AL. 93 MATERIAL AND METHODS Treatment and design Experiment I. Two Japanese Corriedale wethers were fed on a basal diet of timothy hay (CP: 9.1-10.0%) with or without ruminal infusion of acetic, propionic and butyric acids in a repeated measurement cross over experiment (Table 1). Each period lasted for 12 days (7 for preliminary and 5 for sampling). Infusion of acetic and propionic acids were done using the same procedures as described by Fujihara et al. (2002a). Butyric acid was infused at the rate 12 mmol/h during 24 h, which was estimated to be able to supply 150 kcal per day per head. Experiment II. Two crossbred female lambs were fed on three basal diets of hay with or without ruminal infusion of acetic and propionic acids in a repeated measurement crossover experiment also in three periods of similar duration as in experiment one. The three basal hays used were timothy hays (6.6% or Italian ryegrass hay, 7.3% of CP per DM); timothy hay (9.1% of CP per DM); timothy hay supplemented with urea (15.5% CP per DM). The same technique of ruminal infusion of VFA acids used in experiment one was also applied. TABLE 1 Experimental design Experiment I Period I Period II Period III Basal diet (hay) Timothy (B) Timothy (B) Timothy (C) Acid infused acetic acid propionic acid butyric acid Treatment control infusion control infusion control infusion Allocation of animals 1st term* A B A B A B 2nd term B A B A B A Experiment II Period I Period II Period III Basal diet Timothy (A)1 Timothy (B) Timothy (B)+Urea CP of basal diet (%) 6.6 (7.3)1 9.1 15.5 Treatment control infusion2 control infusion control infusion Allocation of animals 1st term* C D C D C D 2nd term D C D C D C # consecutive 12 days for each treatment (7-day: preliminary, 5-day: sampling) 1 in propionic acid infusion, Italian ryegrass hay was used in period I 2 ruminal infusion of acetic acid and propionic acid 94 C2, C3 AND C4 ACID INFUSION AND RUMINATION BEHAVIOUR Animals, diets and management The four sheep (two Japanese Corriedale wethers for Experiment I and II crossbred Suffolk x Japanese Corriedale female lambs for Experiment II), weighing 3845 kg and fitted with ruminal cannulae were used. The sheep were kept in metabolism cages throughout the experimental period. They were fed on 2.0-2.2% dry matter (DM) of each hay per kg body weight per day. Three types of timothy and one type of Italian ryegrass hays were used. Their chemical composition is as shown in Table 2. Before feeding, hay was chopped to about 4 cm long. One-half of the daily rations were given at 09.00 and the other half at 17.00. Fresh water and salt licks containing trace elements were made available at all times throughout the trial. Refusals were weighed, sampled everyday, bulked and sub-sampled every week for their chemical analysis. TABLE 2 Chemical composition of hay diet, % of DM Diet Timothy Italian ryegrass (A) (B) (C) Organic matter 93.71 93.5 94.6 87.1 Crude protein 6.6 9.1 10.0 7.3 Crude fat 2.3 2.5 3.3 2.8 Crude fibre 34.9 32.8 34.7 37.8 NFE1 49.9 49.1 46.6 39.3 1 nitrogen free extractives Sample collection and analytical methods In each experimental period, sampling was done for five days following a seven-day preliminary period. Faeces and urine samples were collected daily from the experimental animals before feeding each morning. The samples for ruminal contents and jugular blood were collected on the final day of the experiment in each period as the same manner in the previous report of Fujihara et al. (2002a). Analytical techniques for chemical analysis of feed, excreta, ruminal contents and blood plasma, and the method for measuring eating and rumination behaviour were similar to those used by Fujihara et al. (2002a). Test for significance of difference between the treatment means for repeated measurement were compared using Mest (Stats View, 1999; SAS Institute Inc., SAS Campus Drive, Cary, NC 27513). The nitrogen (N) balance was indicated as g per kg of metabolic body size to correct a variance metabolism according with different body weight of animals. FUJIHARA T. ET AL. 95 RESULTS Eating behaviour In Experiment I, time spent eating per day was increased in sheep infused with acetic and propionic acids. There were fewer decreases with butyric acid infusion (Table 3). Infusions had no significant effect (P<0.05) on eating time and rate of eating. Infusions with acetic and propionic acids led to decreased rumination appearance (lag time after eating) in sheep while it was increased by butyric acid. In Experiment II however, time spent eating per day did not change with acetic acid infusion and eating time took longer time in sheep fed on low-CP hay (Table 3). Rumination appearance took longer in sheep fed on hay with increasing CP content and was not changed by infusion of VFAs. Daily eating time was prolonged (P>0.05) by infusion with propionic acid regardless the CP content and type of hay eaten. Consequently, eating rate was slightly decreased in sheep fed hay containing variable CP contents. Rumination behaviour In Experiment I, daily ruminating time decreased in sheep infused with acetic acid as compared with those on

journal of animal and feed sciences

The effect of ruminal infusion of acetic, propionic and butyric acids on eating, rumination behaviour and feed utilization in sheep fed on ureasupplemented roughage