Effects of sprouting or roasting cowpeas (vigna unguiculata (L.) walp as protein source in diets for Southern African Windsnyer Type, Large White X Landrace and three -way crossbred growing pigs

Abstract

In poorly resourced settings, livestock feeding options are often narrowed to the affordable, readily available legume grains, and to their most convenient biological or thermal processing methods. The tolerance of different pig genotypes to toxic legume anti-nutritional factors and to the negative impact on dietary dietary nutrient availability may differ. The study aimed to determine the capacity of different local pig genotypes to utilise differently processed cowpeas (Vigna unguiculata (L.) Walp) as a dietary protein source during growth. Preliminary studies were conducted to determine the effective sprouting or roasting of cowpeas for feeding to growing pigs. In a sprouting experiment 1, cowpeas were soaked for 12 hours, open-sprouted over 1, 2, 3 and 4 days, with daily sampling, and the samples rapidly sundried to terminate the sprouting. In a roasting experiment 2, cowpeas were placed in an empty, preheated (150°C interior temperature) cast-iron drum, and roasted for 10, 15, 20, or 30 minutes, coincident with 55°C, 95°C, 105°C, and 130°C respective sample grain temperatures. The effectiveness of both processing procedures was evaluated by determining the in vitro dry matter digestibility (IVDMD) of the processed, compared to raw cowpeas. The IVDMD was estimated using a standard three-step (gastric, small, large intestines) in vitro pig digestion procedure, in a setup modified for micro (0.5 g) sample digestion within Ankom® 57 filter bags. Both the sprouting and roasting in vitro digestion were completely randomised, with 14 replicates per sample. Cowpea samples obtained at key sprouting or roasting points were analised for proximate and detergent fibre components, and for trypsin inhibitor activity (TIA), as auxiliary variable determinants of IVDMD. The steps 1-2 (gastricileal) IVDMD coefficient dropped (p<0.05) in the 2-day (0.78 ± 0.00486) and 3-day (0.77 ± 0.00486) cowpea sprouts, with equally high (p<0.05) step 3 IVDMD for 2-day and 3-day sprouts (0.13 ± 0.00605) compared to 1-day (0.07 ± 0.00605) and 4-day (0.10 ± 0.00605) sprouts. The total (steps 1-3) IVDMD increased (p<0.05) in 2-day (0.91 ± 0.00336) and 4-day (0.90 ± 0.00336) sprouts. Roasting did not affect steps 1-2 IVDMD. The 20-minute (105° C) roasting resulted in high (p<0.05) step 3 (0.17 ± 0.00734) and the total (0.98 ± 0.00449) IVDMD. The compartmental and total IVDMD, and quantitative change in chemical components and TIA indicated 4-day sprouting, and 20-minute (105° C) roasting were respectively most effective for cowpea processing, procedures which were subsequently used to process cowpeas in bulk for a metabolic, and a performance feeding trial. For the metabolic trial, raw (control) and the differently processed cowpeas were used to constitute iso-nutrient (15% CP, 14.17 MJ ME kg-1) maizebased grower pig diets. The metabolic trial used nine growing pigs, three each of Windsnyer (W), Large White (LW) X Landrace (LW) and the 3-way crossbred (W X LW X LR) genotypes. The pigs were inducted into the experiment at respective initial live weights 11.0 ± 1.15. 4 ± 1.15, and 12 ± 1.15 kg. Pigs were randomly allocated to diets for a factorial experiment within three balanced, 3 (genotype) x 3 (period) Latin squares with 12-day feeding periods split into sevenday adaptation, plus five days measurement of feed intake, and the total faecal and urine excretions. Metabolic size-scaled feed consumption was high (122.6 ± 3.01 g kg-1 Live weight (LW) 0.75) for the raw cowpeas, compared to the roasted cowpea diet (108.8 ± 3.01 g kg LW0.75) (p<0.05). On scaled bases, feed consumption was higher on the sprouted cowpeas compared to the raw diet (P<0.05). Sprouting and roasting both reduced the ash digestibility. Ash digestibility was lower (P<0.05) for LW x LR compared to W x LW x LR pigs. Genotype x Diet interaction was observed for ash, fat, ADF and NDF, however the main mean showed non-significant (P<0.05) for fat, ADF and NDF. Pig responses to the differently processed cowpeas were further evaluated in a 60-day growth trial which used a total of 36 animals, twelve male, 28-day weaned pigs of each of the W, LW X LR, and W x LW x LR genotypes (respective initial live weights 15.0 ± 2.3, 39.0 ± 1.4 and 37.0 ± 1.2 Kg). To balance the initial weights across treatments, pigs were blocked by weight within genotype, and randomly allocated within the weight blocks to the experimental diets for a 3 (genotype) X 3 (diets) factorial experiment replicated four times. The experimental diets were a standard, maize-soybean commercial pig grower (control) feed, and iso-nutrient (14.26 ± 1.2 MJ ME kg, 160.0 ± 2.1 g CP kg), roasted or sprouted cowpea-maize grower pig diets. Pig growth and slaughter parameters, visceral organ sizes, and plasma biomarkers of protein, energy utilization, and organ function were measured. Pig growth was different by genotype in the order LW x LR ≥ LW x LR x W > W (p<0.05). Feed intake ranked LW x LR ≥ LW x LR x W > W (p<0.05). Dietary treatments ranked control > sprouted cowpeas > roasted cowpeas diet (p<0.05). The FCR was similar (p>0.05) across the genotypes, but differed by diet in the order control (3.41 ± 0.551) < sprouted cowpeas (4.94 ± 0.551) ≤ roasted cowpeas (5.93 ± 0.551) diet (p<0.05). Back fat was thickest on the control diet (9.91 ± 0.321) compared to the other diets (p<0.05). The W pigs dressed inferior (p<0.05) compared to the other genotypes. Scaled on the metabolic weight, the liver and kidneys were large (p<0.05) in W pigs, and the kidneys enlarged (0.567 ± 0.0105 %) (p<0.05) in pigs on the roasted cowpea diet. The W x L x LR had low alkaline phosphatase activity (99.50 ± 6.090 U/L), W had low creatinine (44.94 ± 2.32 μmol/L) and cholesterol. (1.23 ± 0.0833 mmol/L); and LW x LR had low plasma total protein (69.20 ± 0.915 g/L). Pigs on the sprouted cowpea diet had high (p<0.05) urea (5.30 ± 0.255 mmol/L) and cholesterol (1.82 ± 0.0833 mmol/L). Albumin was low in pigs on the sprouted diet (35.58 ± 0.902 g/L) and on the roasted diet (35.60 ± 0.902 g/L), while alkaline phosphatase activity was high on the sprouted (110.92 ± 6.090 U/L) and the roasted (130.13 ± 6.090 U/L) diet (p<0.05). In conclusion, compartmental and total IVDMD, and quantitative change in chemical components and TIA indicated 4-day sprouting, and 20-minute (105° C) roasting were respectively most effective for cowpea processing. The observed genotype x diet interactions on N balance parameters confirmed genotype influences on the digestive capacity, and intermediary nutrient metabolism in pigs fed the raw, and differently processed cowpeas, which suggested unique adaptive digestive and metabolic traits among the experimental pig genotypes. The underlying mechanisms need further investigation. Roasting and sprouting of dietary cowpeas produced diets which supported similar, slower growth compared to the soybean-based diet, with higher FCR by pigs on the sprouted, compared to the roasted cowpea diet. Further research is recommended to evaluate the cost-effectiveness and practicality of cowpea sprouting or roasting in large-scale pig production systems.