Field study on effects of grinding intensity of feed on performance, androstenone and skatole content in neck fat of male and female finishing pigs

Introduction: The castration of male piglets without anesthesia is under public pressure and is already forbidden in some countries. The fattening of boars is an alternative but due to the accumulation of androstenone (A) and skatole (S) in the fatty tissue, resulting in the so called boar taint, some carcasses may be condemned and therefore excluded from human consumption. Skatole is a product of the microbial tryptophan degradation in the hindgut, which can be lowered by feeding raw potato starch or inulin. Aim of this field study was to find a feeding concept to minimize skatole formation in the digestive tract of pigs. Therefore coarse grinding of a cereal based diet was chosen to reach a higher starch influx into the hindgut mimicking the effects of raw potato starch.

The study was performed with a total of 490 male (m) and 178 female (f) finishers receiving either a finely (F; n=325) or a coarsely ground diet (C; n=343) based on the same ingredients for the last 3-7 weeks of fattening. Diet`s structure was characterized by wet sieve analysis resulting in a different geometric mean diameter (GMD) of 598 µm (F) and 700 µm (C). Twenty pooled fecal samples were analyzed for dry matter (DM), starch content and pH value. Average daily weight gain (ADG) was measured individually over the whole fattening period (27.8-124.9 kg) and feed conversion ratio (FCR) was calculated. Carcass characteristics were monitored by Auto FOM, neck fat samples analyzed for A (ELISA) and S levels (HPLC). Statistical analysis was performed by procedure mixed (SAS 9.1). Differences between LS-means were tested by Scheffe-test p< 0.05.

DM and pH values were significantly reduced in feces of C fed pigs (DM g/kg: C 243, F 264; pH: F 7.24, C 6.99), whereas the starch content was significantly higher (g/kg DM: C 54.6, F 43.3). Feeding regime had no influence on androstenone (ng/g; male: F 1256, C 1236; female: F 171, C 161) or skatole levels (ng/g; male: F 92, C 105; female: F 35, C 38) in the neck fat. Neither ADG of males (g/d: F 890; C 891) and females (g/d: F 854; C 850) nor FCR (both sexes: C 2.47 vs F 2.51) differed between the groups. Under both feeding regimes carcass yield (male: C 75.8%, F 76.7%; female: C 78.6%, F 79.3%), ham weight (kg; male: F 18.1, C 18.0; female: C 18.5, F 18.4) and loin weight (kg; male: F 7.07, C 6.99; female: C 7.26, F 7.23) were lower for the boars.

Although the diet was able to change important fecal parameters no effects on skatole and androstenone contents in neck fat were achieved. Regarding fattening performance, advantages of higher daily weight gain of the boars were not reflected in carcass yield due to the weight of testicles.

Disclosure of Interest: None Declared.