Inducing satiety in sows through nutritional manipulation of gastrointestinal tract volume and volatile fatty acid production

Failure to meet satiation causes feeding motivation to increase. Frustration may be redirected into replacement behaviours (Lawrence and Terlouw 1993) that over time may become stereotypic behaviours or cause aggression. Satiety may be attained by increasing the bulk of the diet. Also of interest is the role of hindgut fermentation of non-starch polysaccharide rich diets, with the production of volatile fatty acids (VFA) from this fermentation having a glucose sparing effect (de Leeuw et al. 2005). Alternative dietary sources that may show effects on satiation include sugar beet pulp (SBP), guar gum, Opticell^® (Agromed Austria GmbH, Kremsmünster, Austria) and magnesium oxide (MgO). This study aimed to investigate the effects of dietary inclusions, aimed to induce satiety through the manipulation of gastrointestinal tract (GIT) volume and (or) VFA production, on blood glucose and behavioural variables in sows.

Fifteen (15) mixed-parity sows (non-pregnant; Landrace X Large White) were housed in individual stalls and offered dietary treatments in a crossover design, such that each sow received each treatment over time. Diets were isoenergetic and isonitrogenous [12.8 MJ digestible energy (DE)/kg, 0.40 g standardised ileal digestible lysine/MJ DE] taking into account experimental inclusions. There were five diets offered: Control diet including no additions; SBP included at 20% of total diet; guar gum (0.5%); Opticell^® (4.0%); and MgO (0.1%). Diets were given for 2 weeks comprising a 1-week period of diet acclimation and then a 1-week period of diet provision, replicated five times, until all sows had received all treatments. Sows were fed twice daily, receiving 60% (1.5 kg) at 0700 h and 40% (1.0 kg) at 1400 h. Behavioural measurements were recorded by scan sampling (1 min) and consisted of individual video monitoring during the 5 min before the first feed, 25 min before the second feed and 45 min after completion of the first and second feed. Behavioural data were grouped into abnormal (oral-nasal) behaviours and postures. The glucose sparing effects of VFA production were monitored through blood glucose measurements (Accu-Chek Performa, Roche, Castle Hill, NSW) which occurred 15 min prior to feed one and two, then at 0.5, 1, 2, 3, 5 and 7 hours after both feeding times. Data were analysed using the GLM procedure (Genstat, 15th Edition; UK).

Blood glucose measurements showed significant effects of dietary inclusions on blood glucose levels (Table 1). The inclusion of guar gum in diets for sows reduced fasting blood glucose levels with significantly lower blood glucose levels before the first feeding. Immediately after feeding, the inclusion of guar gum and Opticell^® resulted in higher circulating blood glucose concentrations (P < 0.05), possibly a result of delayed GIT emptying and (or) reduced insulin sensitivity. Glucose levels of sows receiving guar gum diets returned to fasting levels by 7 hours after feeding. There was no significant effect of treatment on behavioural observations, however time spent displaying abnormal behaviours increased over time (P < 0.05; data not shown) as sows habituated to their stalled environment. Whilst SBP inclusion level was lower in this study, the lack of effect on feeding motivation was unexpected given prior positive effects (Meunier-Salaün et al. 2001). Results of blood glucose sampling suggest all four treatments were able to influence blood glucose levels but the lack of behavioural effect suggests inducing satiety warrants further investigation of economically viable inclusion levels used in this study, in a more stable environment.

Table 1.  Mean blood glucose levels (mmol/L) 15 min prior to, and 30 min and 7 hours after the first feed, in sows fed a control diet or a diet containing 0.5% guar gum, 4% Opticell^®, 0.1% magnesium oxide (MgO) or 20% sugar beet pulp (SBP)