Influence of sex and immunocastration on feed intake behavior, skatole and indole formation in pigs U. Weiler 1, R. Wesoly 1, A. Schmidt 2, M. Otto 3 and S. Müller 4 1: Fachgebiet Verhaltensphysiologie landwirtschaftlicher Nutztiere, Universität Hohenheim, Garbenstraße 17, Stuttgart, Germany 2: Thüringer Lehr-, Prüf- und Versuchsgut GmbH, Am Feldschlößchen 9, Buttelstedt, Germany 3: Mitteldeutsche Schlachtschweineerzeugergemeinschaft w.V., Remsaer Str , Altenburg, Germany 4: Abteilung Tierproduktion, Thüringer Landesanstalt für Landwirtschaft, August-Bebel-Straße 2, Bad Salzungen, Germany Aim of the Study Sex specific feed intake behavior was monitored during the fattening period and consequences for the formation of skatole and indole were studied in boars, barrows, immunocastrates and gilts. Results Data on growth performance and feed intake as well as androstenone, skatole and indole concentrations are given in Table 1. Feed intake/day increased with age due an increase in both, the duration of each meal and the feed intake rate (g/min). This was associated with a 50% reduction in the number of meals/day (see Fig. 1). The time, the animal spent feeding per day changed only moderately with age and revealed a diurnal pattern in all groups (Fig. 2) SKATOLE Gilt n=36 Imm. n=32 Barrow n=33 Boar n=33 Feed intake rate (g/min) **+.10 Time feeding/visit (min) *-.16 Meals/day **-.02 Meal size (g) **-.10 Time feeding/day (min) *-.15 Feed intake/day (kg) Daily gain (g) +.67** **+.19 INDOLE Gilt n=36 Imm. n=32 Barrow n=33 Boar n=33 Feed intake rate (g/min) +.38* Time feeding/visit (min) Meals/day Meal size (g) Time feeding/day (min) * Feed intake/day (kg) Daily gain (g) +.60** Sex and treatment influenced feed intake behavior (Fig. 1): The low feed intake in boars resulted from a reduction in the number of meals/day and the time spent feeding/day. In gilts time spent feeding/day was quite similar to boars, but resulted from a higher number of meals of shorter duration. Barrows had a significantly higher feed intake due to a higher number of meals/day resulting in more time spent feeding/day. The feed intake rate was similar in boars, gilts and barrows. Immunocastration affected feed intake behavior severely, especially the meal size increased dramatically due to higher feed intake rate, which exceeded that of all other groups by 25% at the end of the study. The number of meals per day was not influenced by immunocastration. In gilts and barrows skatole concentrations were significantly related to growth rate (Tab. 2). Additionally the feed intake rate was an important factor explaining the variability in skatole/ indole formation in gilts and barrows, whereas in boars the time spent feeding/day was inversely related to indole concentrations. The physiological mechanisms, however, need further clarification. Fig. 2: Diurnal patterns of feed intake in 10 wk and 24 wk old pigs Fig. 1: Feed intake (kg/d), number of meals / day and feed intake rate (g/min) during the fattening period (mean ± SD) References: 1: Dehnhardt, M., Claus, R., Hillenbrandt, M., Herzog, A. (1993) High-performance liquid chromatographic method for determination of 3-methylindole (skatole) and indole in adipose tissue of pigs J. Chromatogr. 616: ; 2: Claus, R., Mahler, G., Münster, E. (1988) Determination of the boar taint steroid 5α-androst-16-en-3-one in adipose tissue with a rapid microtitre plate enzym-immunoassay (MTE). Arch. Lebensmittelhyg. 89: Table 2: Pearson correlations between skatole/indole and food intake behaviour and daily gain within each group 10 weeks Criteria n giltsimm.barrowsboars Fp< Androstenone (µg/g fat) mean.05 a.10 a.04 a 1.75 b 52, SEM Skatole (ng/g fat) mean34.6 a 60.3 ab 48.8 a 90.3 b SEM Indole (ng/g fat) mean23.3 a 92.1 b 56.7 c 45.3 ac SEM Daily gain (g/d) mean893.1 a 961,0 b 927,0 ab 927,3 ab SEM12,2613,1012,8412,81 Feed intake (kg/d) mean2.28 a 2.79 b 2.69 b 2.23 a SEM Feed conversion (kg/kg) mean2.37 a 2.63 b 2.66 b 2.19 c SEM Methods 36 gilts, 32 immunocastrates (Improvac), 33 barrows (surgically castrated) and 33 boars were studied. Animals were kept in groups 12 pigs of the same sex and treatment with ad libitum feeding (13.4 MJ ME, 17% CP, 1.1% lysine) and continuous recording of individual feed intake behavior by an electronic feeder. Androstenone, skatole and indole were measured in adipose tissue after slaughter (1,2). Table 1: Growth parameter, feed intake and skatole, indole and androstenone concentrations for each sex and treatment group (means, SEM) Different superscripts indicate significant differences p<0.05 by post hoc Tukey test