Other senses may be integral to the social transmission of information related to feeding, although Nicol and Pope (1994) suggested that previous visual cues were more relevant to pigs than olfactory signs in their learning about operant panel pressing. Pigs tended to press panels of a similar colour to the one they had observed the demonstrator using to obtain food.
Social facilitation of feeding is known to occur in pigs, but any attempt to investigate whether or not this might affect daily food intake would be fraught with difficulties of interpretation as it would involve keeping some pigs in isolation, which might be stressful and depress intake. Effects of group and pen size on food intake are discussed in Chapter 17. The relative importance of social transmission of feeding behaviour to pigs is relatively unknown. The importance of individual determinants is likely to vary, depending on the environment and on other current circumstances.
Morganet al.(2001) investigated the extent to which pairing newly weaned piglets with others that had been weaned a week earlier would increase the acceptance of food. Each pair had visual contact and either no physical contact, contact through mesh or penned together, with pairs of inexperienced piglets housed together as controls. The two ages housed together had the highest weight gain and the inexperienced pairs ate less food than the other pairs. Pairs with no experience ate simultaneously on fewer occasions than the pairs in which one piglet was experienced. It was concluded that food intake is stimulated when an inexperienced piglet is housed with an experienced piglet, and it was suggested that this might be exploited to alleviate the post-weaning check in growth.
Cattle
Calves are social drinkers. If one calf is allowed to drink to completion and then another calf in the next pen allowed to drink, the first one starts to consume again. Even when the second calf is muzzled and put in the same pen, it tries to drink and stimulates the first to drink more. Thus it is sensible to provide plenty of teats so that all calves can drink together, in order to achieve maximum intake.
Social facilitation of feeding also occurs in adult cattle, and cows fed in groups have been noted to eat 7% more of a complete food containing 0.6 silage than individually stanchioned cows. In three herds in which first-lactation cows were either mixed with or separated from older cows, the heifers spent more time eating when they were mixed with older cows (263 versus 240 min/day), had more eating periods (6.7 versus 5.3 periods/day) and, in the one herd in which silage intake was recorded, ate more food (9.3 versus 7.7 kg DM/day) (Konggaard and Krohn, 1978). Social interactions do not necessarily facilitate feeding, however, especially if there is insufficient feeding space for all animals in a group to eat at the same time. Trough space can be a limiting factor, and less than 0.2 m/cow is likely to reduce intake.
Heifers can be conditioned with LiCl to avoid eating larkspur, but they lose this conditioning more quickly when kept with unconditioned heifers than when not kept with such untrained animals.
Sheep
Lambs quickly learn to differentiate between their mother and other ewes, the former offering herself for sucking (positive reinforcement), the latter butting and moving away to generate aversion. Lambs show preference for a food with a flavour they experienced in their mother’s milk or even in utero (Nolte and Provenza, 1992).
Provided they are at least 7 weeks old, lambs can learn as well from either their mothers or from other adults. On two commercial farms, ewes and lambs were given grain on three consecutive days. Eighteen months later, 140 of these lambs and 140 naïve lambs were offered grain; all of the experienced ones ate by end of day 3, while less than 10% of the others had eaten by this time (Lynch and Bell, 1987). Thus, the simple strategy of giving ewes grain for a few days just before their lambs are weaned will have a very big beneficial effect if and when these lambs have to be given grain.
One limitation is that the same grain must be given; sheep trained to one grain behave naïvely when offered another. Those which had no previous experience of wheat ate very little of any grain (wheat, barley, oats, maize) in the first 3 weeks of offering, while those which had already had some wheat experience ate wheat from the first day of offering but did not take the other grains as readily, even though they eventually ate more of them than did the totally untrained animals.
Even when sight, hearing and smell are removed, learning is rapid. Sheep introduced to wheat in the presence of experienced sheep start to eat much more quickly than those penned with other inexperienced sheep. When sheep had their sight, hearing or olfaction – or a combination – temporarily impaired, only impairment of all three senses resulted in slower learning, so there is no overriding role for any one sense in the learning process.
When supplementary food is offered in drought conditions in Australia, sometimes sheep fail to eat it and suffer undernutrition or even die. In order to see the extent to which prior experience would alleviate the problem, lambs were offered wheat with their mothers for 5 days for a few minutes each day in one of weeks 1 to 7 of age (Chapple and Lynch, 1986). When, at a much later date they were offered wheat, those which had been given it when 3 weeks or older ate more than those without prior exposure or those exposed in the first 2 weeks of life. Other work showed that lambs given wheat for 5 days subsequently ate much more than those given it for only 2 days. Weaner sheep which had never seen wheat ate almost none for the first 11 days, after which their intake increased rapidly. There is also a fear of unfamiliar troughs, with a reduction in the time taken to eat wheat if it was fed in troughs from which the sheep had previously obtained hay. Sheep must overcome the fear of the trough, the fear of the food and then learn how to prehend, chew and swallow grains.
Provenza et al.(1993) offered ewes a novel food (elm leaves) followed by LiCl or saline, and some of their lambs were conditioned similarly. When lambs were offered a choice, those which were averse themselves, or whose mother was averse, took fewer bites of elm than controls, while there was no difference due to treatment on the number of bites of poplar, which had not been paired
with a toxin and which they had previously eaten readily. It was concluded that the toxin was more effective than the mother in determining preferences, as those lambs that received LiCl themselves avoided elm whether their mother had eaten it or not.
In a further demonstration of the power of observing adults eat, it was found that pre-weaning exposure to molasses-urea blocks had a greater influence on subsequent acceptance than post-weaning exposure.