larger, longer meals. Figure 2.2 shows an example of a 24-h meal pattern of one cow. In this case, nine meals of silage were taken and three allocations each of 2 kg concentrates were dispensed. At 230 min, she tries to get concentrates but is not allowed and diverts her attention to eating silage. Some of the silage meals are protracted and fragmented (e.g. those at 650–750 min), while others are continuous (e.g. that starting at 840 min).
Dado and Allen (1994) have monitored feeding, ruminating and drinking behaviour in lactating cows offered a total mixed ration and have concluded that a Latin Square design with 12 cows monitored for 5 days would be sufficient to detect a 10% difference between means for feeding-related behaviour variables with a probability of 80%.
Sheep
From 2 or 3 weeks of age, lambs spend increasing amounts of time nibbling at food. After weaning they eat by prehending food with their lips and tongue, pulling it back into the mouth for extensive chewing.
Sheep can select well as they have a narrow bite. However, they have a blind area about 30 mm in front of the nose so they can’t see clearly what they are eating! Perhaps they use touch to decide exactly what to eat. When they are selecting actively, e.g. green material from a predominantly dead sward,
Pigs
Auffray and Marcilloux (1983) observed a deceleration in the rate of eating as the meal progressed. ‘Unpalatable’ foods are eaten more slowly than ‘normal’
ones and rate of eating often increases over a period of several weeks as the animals learn that the food is completely safe. It had been assumed that rate of eating would be influenced by the bitter-tasting glucosinolates present in rapeseed meals but, in the work of Lambert et al.(1992), the food eaten most slowly was that lowest in glucosinolate!
Cattle
Faverdin (1985) observed that the rate of eating of a complete food by a lactating cow increased linearly from 50 g/min in the first few days of lactation to 90 g/min in week 9 of lactation. The rate declined as a large meal proceeded, from 120 to about 50 g/min due to longer pauses in actual chewing as the meal progressed. Intake rate at the beginning of the meal is four to five times higher than at the end for cows eating maize silage.
The mean rate at which lactating mature cows ate grass silage (54 g DM/min, Jackson et al., 1991) was very similar to that for lactating heifers eating a complete silage/concentrate mixed food, with an average rate of approximately 50 g DM/min (J.M. Forbes, unpublished observations).
Presumably in systems where food is limited, e.g. dairy cows fed con- centrates in a group, the fastest eaters will consume more and produce more milk, thus rendering themselves more likely to be selected as the mothers of future cows, i.e. selection for fast rate of eating. However, the rate of eating by cows low in the dominance order was found by Kenwright and Forbes (1993) to be significantly faster during the 40-min peak periods after each milking (300 g fresh matter/min) than at a quiet period (10.00–12.00 h) (200 g/min) and the time spent eating significantly less (14.6 versus 18.7 min/h).
The most dominant animals did not eat significantly more quickly during these peak times than at other times of day (270 versus 250 g/min), but spent a little more time eating than at other times of day (19.9 versus 17.6 min). Thus, the dominant cows did not feel under pressure to eat quickly at busy times as they were confident of being able to continue eating when they were hungry.
Rate of eating of concentrates is particularly important when cows are fed in the parlour at milking time. Any cow not having eaten all her allowance when her group has finished milking will hold up the whole group, or miss part of her ration which will then be eaten by the next cow to come into that position in the milking parlour. Inclusion of rapeseed meal in a dairy compound food slows rate of eating, but only to a marked extent during the first two or three foods after the rapeseed is introduced (Frederick et al., 1988). A familiar flavour incorporated in the food successfully prevents this initial slow rate of eating.
Wet food is eaten more quickly than the same food given in the dry form, and Clough (1972) found that cows that ate loose meal at 323 g/min ate pellets at 455 g/min and slurry at 1670 g/min; even though the slurry contained water, the rate of DM intake was considerably higher with the food in this form.
Sheep
Pregnant ewes fed throughout on a complete, pelleted food ate at an average rate of 15 g/min and this increased to around 20 g/min during lactation and to over 30 g/min after weaning (Forbeset al., 1989; Fig. 2.7).
Rates of eating during the first 30 min of the large meal taken after offering fresh hay, chopped dried grass or pelleted dried grass were 7.3, 9.4 and 10.8 g/min, respectively (Forbes et al., 1972). During the second and third 30-min periods there were progressive reductions in the rate of eating. In a further experiment, the same authors penned ewes either singly or in groups of six and fed them on hay either ad libitum or at two-thirds of ad libitum. Rate of eating in the 30 min after giving fresh hay was significantly higher for the lower level of feeding (9.7 g/min) than for ad libitum (8.4 g/min), but only slightly higher for group-fed ewes (9.3 g/min) than for those penned individually (8.8 g/min).
The fact that restricted-fed sheep ate more quickly than those fed ad libitum shows that the latter were not eating at their maximum rate, and therefore that neither jaw fatigue nor lack of saliva were likely to have limited ad libitum intake.
Detailed studies of long meals have shown an exponential slowing of rate of eating. In the example given in Fig. 2.9, the sheep was allowed access to lucerne for only 6 h/day and would therefore have been very hungry at the start of this meal (Baumontet al., 1989).
Fig. 2.9. Cumulative intake of lucerne by a sheep given access for 6h/day: intake (g DM) = 1975(1–e(–0.0044.time)) (from Baumont et al., 1989).