Response in nitrogen balance, fibre digestibility and physicochemical characteristics of digesta in Windsnyer pigs fed on incremental levels of amarula nut cake.

Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.

The broad objective of the study was to determine the response in nitrogen balance, fibre digestibility and physicochemical characteristics of digesta in slow-growing Windsnyer pigs fed on incremental levels of amarula nut cake (ANC) based diets. Thirty clinically healthy growing Windsnyer pigs (21.5 kg ± 4.97) (mean ± standard deviation) were individually assigned to separate pens in a completely randomized design. Five iso-energetic dietary treatments were formulated to contain 0, 50, 100, 150, and 200 g/kg dry matter (DM) of ANC. Six pigs were fed on each experimental diet ad libitum. Pigs were given ten days of the dietary adaptation period. In Experiment 1, nitrogen (N) balance trial was conducted after thirty-one days of feeding pigs with an average body weight of 30.7 kg ± 6.57. The collection of faeces and urine took place every morning at 08h00 for five consecutive days. The hand-picking method was used to collect all faecal material from each pen and those captured by a 1 mm sieve suspended underneath the pen. Urine was collected using plastic trays and treated with 2 ml of sulphuric acid to reduce N volatilisation. The collected samples were frozen at -20 ºC pending analyses. Nitrogen intake (NI), total N excretion (TNE), urinary pH levels, N retention (NR), N absorption (NA), N digestibility (ND), N utilization (NU), net protein utilization (NPU), and biological value of feed protein (BVFP) were estimated. The average daily feed intake (ADFI), average daily gain (ADG), and gain: feed (G: F) ratio were also estimated weekly. There was a quadratic increase in ADFI (P < 0.05), while ADG (P < 0.05) and G: F ratio (P < 0.05) increased linearly with incremental levels of ANC. Nitrogen (N) intake increased linearly with ANC inclusion levels (P < 0.01). There was an increasing quadratic response in NA, apparent ND, and NR in pigs fed on increasing levels of ANC (P < 0.05). A positive linear response in NPU and BVFP to ANC inclusion was observed (P < 0.01). Nitrogen utilization increased at the rate of 0.63 g for each 1 g increase in ANC. There was a negative linear response in TNE through urine and faeces as ANC inclusion increased (P < 0.01). The relationship between urinary pH levels and ANC inclusion was described by the quadratic equation Y = 0.0115x2 - 0.3491x + 4.872 (P < 0.01). In Experiment 2, apparent total tract digestibility (ATTD) of fibre and physicochemical characteristics of colon digesta in growing Windsnyer pigs fed on ANC was determined. The experimental diets were blended with 3 g chromium oxide (Cr2O3) and pigs were acclimatized to this diet three days before the collection period. Representative feed samples for each diet were stored at room temperature pending Cr2O3 analysis. Faecal material was collected using the grab sampling method for five consecutive days between 08h00 and 13h00 and immediately chilled at -20 °C for further analysis. Digestibility of dry matter (DMD), acid detergent fibre (ADFD), acid detergent lignin (ADLD), hemicellulose (HemiD), and neutral detergent fibre (NDFD) were determined. After the digestibility trial, pigs weighing 34 kg ± 6.25 kg were fasted for 24 hours prior to slaughter, and routine abattoir procedures were followed. About 15 to 20 g digesta samples were obtained from the proximal colon and frozen immediately at -20 ºC within 1 hour of collection pending analysis. The DM content, pH level, water retention capacity (WRC), and swelling capacity (SWC) in the colonal digesta were estimated. The digesta pH was determined by inserting Crison 52 02 glass pH electrode immediately after collection. The WRC and SWC were measured using the centrifugation method and modified bed volume technique, respectively. There was a quadratic increase in DMD as ANC inclusion increased (P < 0.01). A positive linear relationship between HemiD and increasing levels of ANC was observed (P < 0.01). There was also an increasing linear response in NDFD as ANC inclusion increased (P < 0.01). Apparent digestibility of ADF and ADL increased quadratically in response to ANC inclusion (P < 0.01). There was an increasing quadratic relationship between digesta DM content and ANC inclusion (P < 0.01). The digesta pH level decreased quadratically with ANC inclusion levels (P < 0.01). The quadratic equation Y = -0.0017x2 + 0.0867x + 3.0929 and Y = 0.017x2 + 0.0389x + 2.9637 described the response in swelling capacity (SWC) (P < 0.01) and water retention capacity (WRC) (P < 0.05) to ANC inclusion levels, respectively. It can be concluded that dietary ANC improves N utilisation and fibre digestibility while reducing N excretion into the environment. Further, fibrous ANC increases the physicochemical properties of colonal digesta, predicting increased fibre fermentation. Hence, ANC can be a potential dietary protein source. Keywords: ammonia volatilization, by-products, digesta properties, dietary fibre, digestion, dry matter content, nitrogen absorption, nitrogen intake, nitrogen utilisation, swine, urinary pH level