Feeding behaviour and diet selection of finishing Limousin bulls under intensive rearing system

Twenty Limousin finishing bulls (initial body weight = 425.9 ± 122.0 kg) were assigned to four balanced groups reared in separate pens with a space allowance of 3.6 m(2) per head and a manger space of 95 cm per head. The finishing period lasted 138 days during which the animals received the same diet provided ad libitum as total mixed ration (TMR) in a single daily distribution at 09:30 h. The average daily gain of the bulls was satisfactory (1.35 ± 0.23 kg per day) and no specific medical treatments were required throughout the finishing period. Three observation sessions of 24 h were carried out at days 23, 78 and 113 to describe bulls feeding behaviour and its partition during three following time intervals after diet delivery (0-8,9-16 and 17-24 h). Average dry matter intake (DMI) was 8.29 ± 0.99 kg per day but the bulls showed a predominant ingestive behaviour during the daylight hours. More than 64.0% of the total dry matter intake was consumed within 8 h from diet delivery with two peaks of eating activity: the first one, right after the diet distribution and the second one around sunset. Feed intake was reduced during the evening (21% of total DM from 8 to 16 h) and overnight (15% the total DM from 17 to 24 h). Bulls spent on average 332 min per day ruminating and this activity was performed mainly after sunset (117 min from 9 to 16 h) and overnight (132 min from 17 to 24 h) during the lying. Diet selection activity performed by the bulls was assessed by measuring the change in particle size distribution and chemical composition of dietary samples taken from each pen at 0 (diet delivery), 8, 16 and 24 h. There was no selection activity within the first 8 h after diet delivery when the eating rate was the fastest (9.1 min/kg DM). In the following time interval (9-16 h), eating rate was slow (15.3 min/kg DM) and bulls performed a selection activity towards the more structured particles (> 8 mm) of the diet. This behaviour may represent an attempt to maintain a sufficient intake of long fibre roughage. Although the pens had a wide manger space, the most frequent eating condition showed one or two bulls standing at the manger at the same time. The simultaneous presence of more than three bulls was rare and it was observed only during the first 8 h after diet delivery when the fresh diet was available.