Effects of ensiled sweet potatoes (Ipomea Batatas) on blood glucose, nutrient digestibility and growth performance of large white x Landrace crossbred male pigs

Abstract

The study comprised two experiments. The aim of the first experiment was to compare postprandial blood glucose changes and the glycemic index responses of growing pigs fed either control (CON), glucose (GLU) or ensiled orange-fleshed sweet potatoes (EOFSP). Nine Large White x Landrace crossbred male pigs weighing 32 ± 2.5 kg BW of same age were housed in pairs and moved into metabolism crates individually for sampling in a temperature-controlled room (ranging from 23.8 ºC to 26.8 ºC). The three pairs were each fed one of control (CON), glucose (GLU) or ensiled orange-fleshed sweet potatoes (EOFSP) alternately after fasting for 12 hours in a crossover design. Glucose concentrations were then measured after meals every 15 minutes for 3 hours. There were no differences in minimum glucose concentration, glycaemic index, fasting glucose and incremental area under curve (P> 0.05) between pigs fed CON and GLU meals. Pigs on EOFSP however had 10.7 % higher GI than those on CON. Pigs on GLU had greater total area under curve and maximum glucose excursion (P < 0.05) than those on CON and EOFSP. The biphasic glucose curve pattern was higher in all treatments (P< 0.05) than the monophasic and triphasic patterns and the pigs on EOFSP diets had a greater proportion of triphasic patterns. The second experiment evaluated the effects of feeding total mixed rations containing EOFSP silage at 5 inclusion levels (0, 8, 16, 24 and 32 %) on nutrient digestibility and growth performance of growing pigs. Thirty Large White x Landrace grower male pigs, weighing between 28.6 ± 5.35 kg BW were blocked by weight and allocated to five experimental diets containing 0, 8, 16, 24 and 32 % EOFSP. A digestibility trial using the total collection method and a growth performance study were undertaken. Pigs that were fed the 32 % EOFSP diet had higher (P<0.05) dry matter digestibility (DMD) than those fed the 16 % diet, while those on 0 %, 8 %, 16 % and 24 % diets had similar DMD (P>0.05). Pigs on the 32 % diet had higher (P<0.05) organic matter digestibility (OMD) and crude protein digestibility (CPD) than those fed 16 and 24 % EOFSP diets. Pigs fed on the 24 and 32 % EOFSP diets had higher neutral detergent fibre digestibility (NDFD) (P<0.05) than those on the 16 % diet. Pigs fed on the control diet had lower acid detergent fibre digestibility (ADFD) (P<0.05) than those fed on 8 %, 24 % and 32 % EOFSP diets. Pigs that were fed 24 and 32 % EOFSP diets had higher (P<0.05) average daily gain (ADG) than those fed CON and 8 % EOFSP diets. Pigs that were fed the 32 % diet had higher (P<0.05) average daily feed intake (ADFI as is) than those fed the CON, 8 % and 16 % EOFSP diets. Pigs fed the 8 % and the 32 % diets consumed more ADFI (DM) than those on the CON diet. Pigs that were fed the CON diet had lower (P<0.05) feed conversion ratio (FCR as is) than those fed the 8 % diet. There was no difference (P>0.05) in FCR (as is) in pigs fed the CON, 16 %, 24 % and 32 % EOFSP diets. Pigs fed the 8 % diet had higher FCR (DM) (P<0.05) than those fed the 16 %, 24 % and 32 % diets. Given that it has been demonstrated that a high GI prompts an increase of insulin over time which enhances feed intake it can be concluded that the 10.7 % higher GI in pigs fed EOFSP than the CON fed pigs could translate to higher feed intake and better growth performance of pigs. It was also concluded that ensiled orange-fleshed sweet potatoes can be incorporated in growing pig diets up to 32 % with no negative impact on digestibility of nutrients and growth performance.