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.
but there was no difference between deprivation periods (0.29, 0.62, 0.65, 0.57 m/s, respectively), suggesting that 0.65 m/s was the fastest they could run.
Food restriction is sometimes used to delay puberty in pullets. When pullets were subsequently restricted to that weight of food eaten voluntarily at 6 weeks of age (45 g/day), the birds ate and pecked at empty feeders for the same amount of time per day as ad libitum controls spent eating, i.e. there was no increase in attempts to get food, as is seen in more severe types of underfeeding.
Broiler breeder stock are usually restricted to less than one-half of ad libitum intake. Such animals have a high rate of working for food, even just after their ration has been consumed, and are highly motivated to eat at all times (Savory et al., 1993). If offered food ad libitum after a period of restriction, at first they eat up to three times the restricted daily level, gradually falling to about double the restricted level (de Jonget al., 2003).
When food was returned to cockerels of an egg-laying strain after food deprivation, the rate of eating was higher after a 24-h fast than after a 2-h fast, but there was no further effect of 48 h (Wood-Gush and Gower, 1968). It is likely that the size of the first meal after a long fast is limited by the capacity of the crop, which acts as a storage organ, the distension of which inhibits feeding.
Rather than restrict intake by offering weighed amounts of food, it is often more convenient to give access to unlimited amounts of food for limited periods of time. Cockerels of a layer strain allowed food for one or two periods of 2 h each per day ate 65 and 80%, respectively, of the amount eaten by control groups with 24 h/day access and, somewhat surprisingly, they did not increase their intake as they became accustomed to the situation (Barachet al., 1992).
In a review of the welfare of poultry in modern production systems, Mench (1992) discusses food deprivation and restriction which pose a welfare dilemma as, if fed ad libitum, broiler breeders experience reduced fertility and health problems, yet if fed at the usual severely restricted level they are hungry for most of the time. The welfare aspects of feeding restricted amounts of food or imbalanced foods are discussed further in Chapter 18.
Pigs
There was a linear increase in the weight of food eaten by growing pigs during the first meal after deprivation of 1–6 h (M. Corbett, S. McNicholas and J.M.
Forbes, unpublished observations).
Restriction of protein intake in pigs has been shown to cause increased rooting and general activity, suggesting that specific nutritional needs increase foraging motivation (Lawrence et al., 1993). Restriction of food intake gives rise to increases in ‘working’ for food in an operant conditioning situation, but normal farm environments do not provide facilities for foraging. Therefore, animals develop stereotypies such as chewing chains; ingestion of even a small amount of food stimulates such activities. Pregnant sows are usually restricted to about 60% of their ad libitum intake and such animals have a high rate of working for food, even just after their ration has been consumed. In order to
Feeding Behaviour 35
give sows a more natural way of getting food by working for it, a feeding ball has been developed that delivers food pellets at random intervals if it is rolled around (Young and Lawrence, 1993). The lower the level of feeding, the more sows push the ball around.
Quite severe food restriction of boars makes them much more willing to press a button to obtain small rewards of food, compared with those fed almost ad libitum (Lawrence et al., 1989). When the bulk of the restricted ration is increased by incorporating straw, there is no reduction in operant responding, showing that the mere presence of bulk in the digestive tract is not satiating.
However, pregnant gilts and sows given restricted amounts of food with different levels of fibre showed a significant reduction in stereotypies with higher fibre foods, and so Robert et al.(1993) concluded that bulky food may be beneficial for the welfare of pregnant sows.
Pigs spend a considerable amount of time chewing materials in their environment, but it is unclear whether this reflects motivation to feed, to explore or a combination of both. By providing a tube containing water, saccharin solution or sucrose solution, Dayet al. (1996a) were able to separate these possibilities. They observed that chewing at the plain water tube was at a low level and not affected by the degree of food deprivation. Saccharin only slightly increased chewing whereas sucrose, which provided energy as well as a sweet taste, caused large increases in chewing activity, especially in food- deprived animals, demonstrating that nutritional feedback during exploration modifies foraging behaviour towards correction of energy deficiency.
Cattle
The intake of hay by cows increased by 20% as the increase in time of access to food was increased from 5 to 24 h/day, in contrast to an 80% increase in intake when the food was a concentrate mixture (Freer and Campling, 1963), suggesting a physical limit to intake of the hay. Daily access for at least 6 h is necessary for maximum intake of silage by beef cattle (Wilson and Flynn, 1974). Dry cows ate 8.0 kg/day when given access to silage for 5 h/day, while those with continuous access ate 10.1 kg (Campling, 1966).
Sniffen and Chase (1987) observed that mildly intake-restricted cows (100% of calculated net energy requirement) ate an average of 4.4 meals daily, compared with an ad libitum group (111% of net energy (NE) requirement) that ate 12.4 meals.
Sheep
When sheep were given access to hay cubes for 3, 6, 12 or 24 h/day, intakes were 1502, 1869, 2086 and 2413 g/day (Hidari, 1981). With fasts of 1–6 h, sheep fed on a pelleted 0.5 dried grass:0.5 barley compound food compensated for the fasting period in the first two or three meals after the food had been
replaced and there was no effect on daily intake (J. Black, F. Carey-Wood and J.M. Forbes, unpublished observations).