Effect of dietary fibre on the behaviour and health of the restricted fed sow

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Abstract

The usual restricted feeding level during gestation, whilst adequate to maximise economic performance, might not fulfil behavioural needs of the sow. Hunger and frustration of feeding motivation have been linked to the occurrence of stereotypic activity, and accentuate aggression and feeding competition in group-housing systems. Incorporation of fibre in diets to increase bulk, without changing the daily dietary energy supply, has been shown to result in at least a doubling of eating time, a 20% reduction in feeding rate, a 30% reduction in operant response in feed motivation tests, a reduction of 7–50% in stereotypic behaviour, and a decrease in general restlessness and aggression. Results suggest a reduced feeding motivation, but only if nutrient intake with fibrous diets meets the nutrient requirements of the animals. Investigations of circulating glucose, insulin and volatile fatty acid levels in sows fed fibrous diets indicate a more constant nutrient absorption and greater microbial fermentation in the gut, which should increase satiety. There is inadequate information on effects of dietary fibre on physiological stress and health. In addition to welfare considerations, a range of technical requirements and economic factors must be considered when making decisions on the use of dietary fibre during gestation.

Introduction

Breeding sows are commonly fed to maintain a relatively constant body condition throughout the reproductive cycle for good health and optimal performance (Dourmad et al., 1994, Dourmad et al., 1996). This involves a restriction of feed intake during gestation to prevent excess body weight gain and fat deposition, as these cause farrowing and locomotion problems and subsequently lower reproductive performance. Excessive underfeeding in pregnant sows leads, however, to reduced piglet birth weight and viability, low body fat reserves at farrowing and at weaning, associated with delayed return to oestrus and low conception rate. On the other hand, a high feeding level in lactating sows is necessary to ensure the high nutrient intake required for maintenance and milk production. In all cases, excessive feed restriction will be detrimental to good reproductive performance.

Pregnant sows typically receive their whole daily feed in one or two small, concentrated meals which are rapidly consumed. This practice supplies requirements for maintenance, and a small additional allowance for growth of maternal tissue and conceptus, and is adequate to ensure good health and performance. However, these conditions might not fulfil other needs of the sow, especially her feeding motivation. Indeed, the level of feed provided corresponds to about 0.40–0.60 of the voluntary intake (Petherick and Blackshaw, 1989, Brouns et al., 1995), which results in a low level of satiety and a reduced performance of appetitive and consummatory sequences of the feeding behaviour. A low feeding level has been linked to the occurrence of stereotyped activities, which are described as behavioural patterns performed repetitively in fixed order and with no apparent function. These behaviours are more prevalent in the immediate post-feeding period, and have been attributed to the limited nutrient supply in combination with the reduced access to a foraging substrate in stalled or group-housed sows (Rushen, 1984, Rushen, 1985, Appleby and Lawrence, 1987, Terlouw et al., 1991, Lawrence and Terlouw, 1993, Spoolder et al., 1995). The occurrence of stereotyped behaviour has been considered to reflect heightened feeding motivation after feeding and interpreted as an indication of impaired welfare (Wiepkema et al., 1983). In addition, a restricted feeding supply can lead to feeding competition in group-fed sows and restricted individual access to the feed. Unequal intake between sows within the group has detrimental effects on body reserves, especially for the low-ranking sows (Czermely and Wood-Gush, 1986, Edwards, 1993, Signoret et al., 1995).

Under increasing public pressure and reinforced implementation of European legislation on welfare, doubts have emerged on the welfare status of pigs in intensive production systems. The inability of pregnant sows to express spontaneous feeding motivation fails to satisfy one of the five basic requirements of welfare status considered in legislation: freedom to express normal behaviour (Council Directive 1991 630/EEC). Nevertheless, the high intake capacity of pregnant sows limits any attempt at offering a conventional diet ad libitum because of concomitant obesity and detrimental effects at farrowing and during lactation. An alternative way of satisfying feeding motivation whilst maintaining sows on restricted energy supply, is to provide diets with additional roughage. Fibrous materials can be provided in the environment, in a rack or on the floor, or by including high levels of fibrous ingredients in the diet, allowing increased feed bulk without increasing the energy and nutrient allowances.

Sows show a high capacity to digest fibrous diets (Noblet and Shi, 1993). The effects of dietary fibre have been studied with regard to their nutritional and metabolic effects, and their consequences on performance (Etienne, 1987, Close, 1993). More recently, attention has been paid to the effects of dietary fibre on behaviour and health of feed-restricted sows, in relation to animal welfare considerations. The objectives of the present review are to describe the major results of such studies and evaluate the potential beneficial effects of dietary fibre for the improvement of animal welfare.

Section snippets

Effects on behaviour

Investigations of the effects of fibre on behavioural activity have focused mainly on feeding motivation, measured on the basis of various criteria including the appetitive and consummatory behavioural sequences of the feeding activity (Lawrence and Terlouw, 1993), the feeding rate (Brouns et al., 1997) or the response level in operant conditioning procedures (Lawrence and Illius, 1989). Aggressive behaviour has also been considered in group-housed sows in connection with potential feeding

Effects on health

Fibrous diets induce behavioural changes in pregnant sows. These diets can fulfil the feeding and foraging motivations, and thus improve the ability to meet behavioural needs. Nevertheless, welfare considerations also include health status, physiology stress responses and performance levels.

Conclusion and perspectives

This review shows that future research should move away from looking at the effects of fibre in general, and focus instead at the more specific effects of different types of fibre on behaviour and physiology. Concerning the feeding rate, as pointed out by Brouns et al. (1997), it is not yet known if the physiological variables governing satiety, e.g. gastrointestinal distension and metabolic changes, act independently or as a single composite variable. In order to get this deeper understanding,

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