Doctoral Degrees (Animal Sciences)

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Browsing Doctoral Degrees (Animal Sciences) by Subject "Antimicrobials"

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    Feed supplement and meat preservative potential of grape pomace (Vitis vinifera) in lamb production
    (Stellenbosch : Stellenbosch University, 2019-03) Chikwanha, Obert Chenjerayi; Mapiye, Cletos; Muchenje, Voster; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: The objective of the overall study was to evaluate the potential of grape (Vitis vinifera L.) pomace (GP) as a feed supplement and meat preservative in lamb production. Pomace from two red grape (Pinotage and Shiraz) varieties and one white grape variety (Sauvignon Blanc), were collected from the Welgevallen cellar to evaluate the effect of drying method [sun (7 d), oven (60 °C for 72 h) and freeze] on the nutrient composition and in vitro ruminal neutral detergent fiber (ivNDF) digestibility. Overall, sun- and oven-dried Shiraz GP were characterized by a higher dry matter, crude protein, NDF, acid detergent fiber and lignin content, compared to the other drying × variety combinations. Freeze- and oven-dried Pinotage GP were characterized by the highest mineral content, compared to freeze-dried Pinotage GP that had the most comprehensive amino acid profile and highest ivNDF digestibility at 24 and 48 h for both parameters and time periods. The second study assessed the impact of drying method on the retention of bioactive compounds and biological activities of the three types of GP. Freeze-dried Sauvignon Blanc GP had the highest proanthocyanidin content and exhibited the highest antioxidant activity relative to other drying × variety combinations. Overall, freeze-dried Shiraz GP had the most comprehensive fatty acid profile and highest phenolic content compared to other treatment combinations. Based on the nutrient composition, the low proanthocyanidin content, the availability and the fact that it is a unique South African cultivar, Pinotage GP was selected for subsequent trials. The effect of supplementing sun-dried Pinotage GP on nutrient utilization in finisher lambs was evaluated. Twenty-one Dohne Merino lambs [51.6 ± 4.70 kg body weight (BW)] were randomly assigned to a control diet group (no GP), and two treatments groups containing 100g and 200 g GP/kg diet dry matter (DM), respectively. Increasing the inclusion level of Pinotage GP in the lamb finisher diet resulted in a linear decline in carbohydrate intake, total volatile fatty acid concentration, microbial nitrogen (N) yield, and total purine derivatives excreted. No adverse effects on retention and efficiency of N utilization were observed with the GP-containing diets. A follow up study assessed the effect of sun-dried Pinotage GP supplementation in lamb diets on growth performance, and carcass traits and meat quality attributes. Forty Dohne Merino lambs (32 ± 1.7 kg BW) were randomly assigned to five experimental diets that comprised a control (no GP), and four GP-based diets consisting of 50, 100, 150 and 200 g GP/ kg, respectively. Dry matter intake (DMI), average daily gain (ADG) and carcass traits for lambs were influenced by the addition of GP without negatively affecting meat quality traits. The optimum inclusion levels of GP for DMI and ADG were observed at 113g/kg and 96 g/kg, respectively. The last experiment evaluated the sensory quality and shelf life of retail displayed meat of lambs fed increasing levels (i.e., 0, 50, 100, 150 and 200 g GP/kg). Overall, the 150 and 200 g GP/kg diets resulted in higher antioxidant activity, and reduced lipid and protein oxidation occurring during retail display, compared to the 0 to 100 g GP/kg diets. Microbial loads increased during the retail display, but at a lower rate for the 150 and 200 g GP/kg diets. Diet had no negative organoleptic effect on the sensory quality of the lamb. Overall, the inclusion of GP improved production and shelf life without compromising meat physicochemical and sensory qualities. Based on the experimental evidence, it can be concluded that GP can be used as an alternative supplement and meat preservative by the red meat industry.