Diets contained similar protein and energy levels of 13% and 18MJ/kg DM, respectively. The diets met recommended nutrient requirements for slow-growing sheep (NRC, 2007). Diets had similar nutrient contents except purified condensed tannins ranging from 0 to 50g/kg DM. These diets were, therefore, appropriate for the determination of condensed tannin levels for optimal performance and reduced methane emission in yearling male Bapedi sheep. It was expected that the diets would have similar intake and digestibility values (McDonald et al., 2011) provided that condensed tannin supplementation did not have any adverse effects. Indeed, supplementing diets with purified condensed tannins did not affect intake, digestibility and weight gain of male Bapedi sheep. It is possible that the purified condensed tannin amounts were not too high to adversely affect intake, digestibility and weight gain of male Bapedi sheep. Al-Dobaib (2009) also reported that lambs fed diets having different levels of quebracho tannins had similar intakes and weight gains. However, other studies showed a decrease in intake and digestibility of nutrients when condensed tannins were incorporated into the ruminant diets (Makkar, 2007). The binding ability of tannins to microorganism cell walls adversely affects enzyme secretion and nutrient transportation within the organisms (McSweeney et al., 2001); thus, nutrient digestibility decreases because rumen microorganisms are not able to optimally ferment the diets. However, other studies found that condensed tannin inclusions in the diets had beneficial effects on intake and weight gain of ruminant animals (Min et al., 2003; Soltan et al., 2012).
Diet supplementation with purified condensed tannins reduced methane emission by Bapedi rams, by 51 to 60%. A 49.08g supplementation of purified condensed tannins per kg DM diet was calculated, with the use of quadratic equations, to optimize methane emission reduction by male Bapedi sheep. This indicates that condensed tannin levels used in the study were enough to inhibit methanogenesis (Makkar et al., 2007). Carulla et al. (2005) observed a 12% reduction in methane emission when sheep were fed diets having different levels of condensed tannins. The authors indicated that tannins reduced methane production by decreasing synthesis of acetate during digestion. Woodward et al. (2001) reported a 20 to 24% decrease in methane emission when sheep were fed diets containing condensed tannins. The present study indicates that purified condensed tannin supplementation levels of 30, 40 and 50g per kg DM diet resulted in similar methane emission levels by sheep; possibly meaning that the levels used were within the required effective amounts for inhibition of methanogens in sheep. Mbanzamihigo et al. (2002) observed similar methane emission amounts by sheep when fed diets with tanniniferous legume supplementation levels of 0.16, 0.35, 0.41 or 0.51g/kg DM.
Nutritional problems can be detected in the blood of animals (Ajao, 2013). In the present study, purified condensed tannin supplementation levels of 0, 30, 40 or 50g per kg DM did not affect blood parameters of male Bapedi sheep. Amounts of purified condensed tannins used induced no adverse effects in the animals. Haemoglobin values observed are normal for a health sheep (Daramola et al., 2005; Akinyemi et al., 2010; Akinrinmade and Akinrinde, 2012). The present results findings are like those of Dey et al. (2008) and Pathak et al. (2013). Purified condensed tannin supplementations did not affect haematocrit values of male Bapedi sheep, indicating that the animals were not anaemic (Purves et al., 2003; Ndlovu et al., 2007). Solaiman et al. (2010) and Brown et al. (2016) observed similar results in goats on diets differing in tannin amounts.
There were no significant variations in white blood cell (WBC) counts of Bapedi sheep on diets differing in purified condensed tannin supplementation levels, indicating that the animals were in good health (Ahamefule et al., 2008; Solaiman et al., 2010). Brown et al. (2016) observed similar results in Bapedi goats on diets differing in tannins.
Purified condensed tannin supplementation did not affect blood urea values of male Bapedi sheep. The blood urea values are within the range for a health sheep (Daramola et al., 2005; Akinyemi et al., 2010). Serum glucose values of male Bapedi sheep were not affected by dietary supplementation with purified condensed tannins, and they are within the normal range for a health sheep (Naumann et al., 2017; Pathak et al., 2013; Midaoui and de Champlain, 2005).
Blood cholesterol values were similar among Bapedi sheep fed diets with different levels of purified condensed tannins. These cholesterol levels, ranging from 2.42 to 3.3 mmol/L, were within the normal values for a healthy sheep (Naumann et al., 2017; Siri-Tarino et al., 2010). Olafadehan et al. (2014) observed similar cholesterol values when goats were on diets high in condensed tannins. Supplementation with purified condensed tannins did not affect blood protein indices of male Bapedi sheep. The blood protein indices were normal for a healthy sheep (Naumann et al., 2017; Jain, 1986).
Purified condensed tannin inclusion in the diet had no effect on serum enzyme levels of Bapedi rams, suggesting that the animals were in good health (Thapa and Walia, 2007). Dey et al. (2008) observed no effects of tanniniferous Ficus infectoria leaf meal supplementation on aspartate transaminase and alanine transaminase levels in lambs. Purified condensed tannin supplementation levels did not affect blood electrolytes and mineral values of Bapedi rams. The electrolytes and mineral values obtained were normal for healthy sheep (Naumann et al. (2017), possibly meaning that the amounts used did not affect mineral absorption in the gut of the animals (Naumann et al. (2017; Sowande et al., 2008).
Condensed tannin supplementation did not adversely affect male Bapedi meat pH, sensory attributes and shear force values. The amounts 0, 30, 40 or 50g of purified condensed tannins per kg DM diet did not affect the end products of digestion and hence no differences in meat attributes of the sheep were expected. Dentinho et al. (2020) observed similar results when lambs were fed diets having different tannin levels. Similarly, Brown and Ngámbi (2018) observed no differences in goat meat attributes when diets differing in Vachelia karroo leaf meals were fed to goats. However, Luzardo et al. (2019) and Luciano et al. (2009) observed that tanniniferous feeds improved meat colour of sheep. Gesteira et al. (2018) concluded that lamb meat tenderness decreased and shear force values increased as dietary tannin levels increased. Kobue-Lekalake et al. (2009) and Priolo et al. (2000) observed that meat of lambs on diets with lower tannin levels had better taste. The present study indicates that purified condensed tannin supplementation levels did not affect Bapedi sheep meat pH values which were within the range for a healthy sheep (Mostert, 2007). Priolo et al. (2002), also, observed that tannin supplementation had no effect on sheep meat pH values. However, other authors reported increased meat pH values when sheep were supplemented with purified condensed tannins (Ngambu et al., 2013).
Purified condensed tannin supplementation levels of 30, 40 or 50g/kg DM diet increased antioxidant activity values in ram meat. Sufficient uptake of dietary antioxidants has been observed as an effective method to prevent lipid oxidation and avoid oxidation of cells and tissues caused by excess free radicals and oxidative stress (Negukhula, 2010). High antioxidant activity values in meat increase the quality and shelf-life of meat by reducing lipid oxidation (Fernandez-Gines et al., 2005; Karami et al., 2011; Juarez et al., 2012; Kasapidou et al., 2012; Karre et al., 2013). Marume et al. (2012) found that Diet supplementation with tanniniferous Acacia karroo leaf meal improved goat meat sensory attributes (Marume et al., 2012). Velasco and Williams (2011) also reported that chicken meat sensory attributes can be improved by inclusion of antioxidants in the diets.