In order to see the extent to which birds learn to anticipate a fast, Petherick and Waddington (1991) housed pullets individually in a circadian-free environment and, on days 17–47, 50% were shown a coloured card during the final hour of food availability, prior to food deprivation of 8 or 12 h. There was no indication of increased intake during this period and so no suggestion that they could learn to use the colour cue to anticipate a fast. Do they learn when dusk is approaching by the number of hours since dawn?
Pigs
There are two peaks of feeding, one in the morning and one in the early afternoon (de Haer and Merks, 1992) but Fig. 2.11 shows that the second is by far the greater. Note than some feeding still takes place at night and that there is little effect of single versus group penning. However, examination of the data in more detail showed that, in groups, 69% of meals accounted for 87% of intake and 83% of eating time. With individual housing, only 39% of meals contributed 90% of the food eaten and 79% of the feeding time.
In other words, there were a lot of small, short meals when pigs were kept individually, compared with when they were in groups; with group feeding there can be considerable competition for a single feeder, resulting in many interrupted meals and therefore fragmented feeding behaviour. The repeatabilities of day-to- day recordings of intake traits were high within 2-week periods compared with months or the whole fattening period, indicating a steady change in feeding behaviour as pigs grow.
The difference in behaviour between day and night is likely to be a result of social constraints, but may also represent a reluctance by the animals to feed Fig. 2.10. Intake of grazed herbage (●) and silage (䡲) by lactating cows after various lengths of fast (from Patterson et al., 1998).
at night. The two daylight feeding peaks may be coincidental with the entrance of the stockperson into the animal house or may be the preferred feeding times of the pigs.
Cattle
A high level of feeding activity is usually observed after fresh food is offered. A smaller peak often occurs before sunset and another just after midnight. Data from individual young bulls fed from automatically recording feeders showed that the sunset peak moved according to the time of year and that the night- time quiet period was longer in winter (Stricklin, 1988). In another trial, cattle were either trough-fed or fed from a single automatic feeder. While those fed from the trough showed a normal diurnal pattern of feeding, those on the single-space feeder ate at any time of day or night, presumably due to competition. Trough-fed cattle spent about 120 min/day feeding compared with 80 min/day for those on the single feeder.
Under conditions where little competition for feeder space exists, dairy cows eat few meals from around 01.00–06.00 h. When there are more animals than feeder spaces there is strong competition at busy times, particularly after milking and when fresh food has been delivered. Kenwright and Forbes (1993) observed a clear triphasic pattern of eating in cows milked three times per day, peaks of feeding activity occurring during the periods after return from milking, including large meals, which shows that some cows were monopolizing feeders, thereby preventing others from eating at that time. The more dominant animals
Feeding Behaviour 33
Fig. 2.11. Diurnal patterns of feed intake in group-housed growing pigs. The three lines represent different batches of animals (from de Haer and Merks, 1992).
ate less at night (01.00–06.00 h) than those at the bottom of the ‘pecking’ order.
Therefore, heifers low in the social dominance order might not be able to satisfy fully their desire to eat when the level of competition for feeding space was high.
The high incidence of aggressive interactions during the period immediately after return from milking has implications for the health and nutrition of the animals.
The fact that lower-yielding cows were lower in the dominance order (calculated according to Rutteret al., 1987) than high yielders but ate more at night suggests that high demand for nutrients was not the prime cause of nocturnal eating, although it is possible that low dominance caused low intake, resulting in lower milk yield. It is more likely that those lower in the dominance order were prevented from meeting their needs during the day and were thus forced to satisfy their requirements by eating in the middle of the night. When they did manage to eat at the most popular times of day it was in short meals, eaten at a rapid speed and terminated by the arrival of a more dominant animal.
What are the implications of these findings for the management of dairy herds? Jackson et al.(1991) suggested that, up to a ratio of 3.5 cows/feeder, there was no effect on daily intake of silage, while Elizalde and Mayne (1993) have shown that, although feeding behaviour is affected with 5 or more cows/feeder (increased rate of eating and shorter total feeding times), it is not until there is a ratio of 7 cows for each feeder that daily intake of silage becomes depressed.
Sheep
Sheep show similar light-entrained circadian rhythms of feeding to cattle (see Fig.
17.7). Another factor affecting feeding rhythms is environmental temperature:
sheep do not eat in the hottest part of the day when the heat load is so great that they must seek shelter.