Effects of dietary supplementation of condensed tannin and calcium nitrate in total mixed rations on long-chain fatty acid metabolism and carcass characteristics of dohne merino lambs

Abstract

For a methane mitigation strategy to be sustainable it must either have no affect on product quality or have an added cobenefit in terms of improving the quality of meat. This study evaluated the effect of Acacia mearnsii (as a source of condensed tannin) and calcium nitrate used as anti-methanogenic additives on carcass characteristics and meat quality. This study evaluated the effect of 1% urea or 3.2% calcium nitrate (CaN) as a non-protein-nitrogen (NPN) source in a total mixed ration (TMR) with or without the supplementation of 4.2% Acacia mearnsii tannin on carcass characteristics, fatty acid metabolism and hematological parameters of Dhoné Merino lambs. Forty lambs averaging 34.7±4kg were blocked according to weight and sex. Within each block lambs were randomly assigned into one of four treatment groups: Urea-based TMR, Urea-based total mixed ration with tannin, CaN-based TMR and CaN-based total mixed ration with tannin. Two lambs were assigned per pen and each pen was replicated five times. Lambs were adapted to the ration over 21 days. Four ewe lambs from each treatment and four ram lambs from each treatment were randomly assigned to this study and fed beyond 60 days in the trial. On day 61 hematological and serum samples were taken from the jugular vein of those 32 lambs. Lambs were slaughtered between 61 days and 103 days on trial. Four sheep (two ewes and two rams from each treatment group) were slaughtered at a lighter weight (45kg<2n<48kg and 50kg<2n<55kg, respectively) and four sheep (two ewes and two rams from each treatment group) were slaughtered at a heavier weight (48.1kg<2n<51kg and 55.1kg<2n<60kg, respectively). Acacia Mearnsii, a condended tannin supplement (also referred to throught out the dissertation as ‘tannin”) increased the days on trial and decreased the cold carcass weight (CCW) and dressing percent (D%; P<0.005) of lambs. The tannin supplement had no effect on body composition, liveweight (LW), subcutaneous fat depth (SCF; over the 8th and 10th ribs), eye muscle area (EMA), carcass pH or temperature (P>0.05). Although tannin treatment had no effect on the percent of moisture and ash in the longissimus dorsi, there was an increase in the percent of ether extract (EE%; P<0.01). Calcium nitrate did not affect any of these parameters (P<0.05), except for a decrease in D% (P=0.05). The sex of the lambs affected all parameters except for carcass pH and temperature (P>0.05). Ewes took longer to reach their light and heavy slaughter weights than rams (P<0.05). In terms of body composition, ewes increased fatness and decreased muscle and bone percent (P<0.001). In accordance with this, ewes increased SCF depth over the 8th and 11th ribs (P<0.010 and P=0.001). As a result, moisture was higher in rams (P<0.01) and EE% was higher in ewes (P<0.001). Cold carcass weight (CCW) and EMA were greater in rams and D% was higher in ewes (P<0.005). Slaughter weight had no effect on body composition (P<0.05), D%, carcass pH, temperature or days on trial (P>0.05). However, CCW, EMA and SCF depth were greater in heavier lambs (P<0.001 CCW, P<0.05). Between day one and six post slaughter, redness (a*) and Chroma (C) increased in the Longissimus dorsi, regardless of the treatment and sex (P<0.001). Tannin treatment and CaN had no effect on lightness (L*), redness (a*), yellowness (b*) or hue angle (h) on day one (P>0.05). By day six post slaughter CaN had a lower a* (P<0.05). Tannin had no effect on colour on day six (P>0.05). Lightness (L*), a*, b* and C did not differ in the colour of SCF when tannin was supplemented in the diet. Hue angle (h) increased when CaN was supplemented (P<0.05). Ewes had higher L*, a* and C on day one post slaughter (P<0.05) but by day six there was no difference between the sexes (P>0.05). Heavier lambs had an increase in L* and h on day one (P<0.05 and P<0.01, respectively) but by day six there were no differences between the weights for any of the colour parameters (P>0.05). The colour of SCF was not affected by weight (P>0.05), but a* was higher in ewes (P<0.05) and h was higher in rams (P<0.005). Calcium nitrate had no effect on albumin and hematocrit, but it increased cholesterol and blood urea nitrogen (BUN) (P<0.05). The adaption of lambs to the diet was sufficient as there were no morbidities or mortalities during the duration of the trial. The cholesterol was within the South African Mutton merino range published by Akanmu et al. (2020) of between 1.42 and 1.53mmol/L. Tannin did not affect the molar percent (w/w%) or gravimetric concentration (mg/g sample) of total saturated fatty acid (SFA) in subcutaneous fat (SCF), intramuscular fat (IMF), perirenal fat (PRF) and rumen fluid (RF; P>0.05). Monounsaturated fatty acid (MUFA) only decreased gravimetrically in SCF (P<0.05) but not IMF, PRF or rumen fluid (P>0.05). Tannin increased the percent of polyunsaturated fatty acid (PUFA) in SCF and PRF (P<0.05) and increased its gravimetric concentration in IMF and PRF (P<0.05). Tannin increased the PUFA/SFA ratio gravimetrically and as a percent of total fatty acids in IMF, SCF and PRF (P<0.05), apart from the gravimetric concentration in IMF (P>0.05). Fatty acid health indices showed no effect of tannin on the nutritional value of the fatty acid profile of the longissimus dorsi. The gravimetric desirable fatty acids were lower (DFA; P<0.05) due to reduced major fatty acid, C18:0 (P<0.05). Both hypercholesterolaemic (h) and hypocholesterolaemic (H) fatty acids were also lower (P<0.05). A lower gravimetric concentration of fat in the SCF could describe these lower indices (P<0.05). Rumen fluid was analysed for fatty acid composition to get an indication of how the treatments were affecting the microbial activity and biohydrogenation patterns. No affect in the biohydrogenation ratios (P>0.05) suggest that rumen microbes were unaffected by the supplementation of Acacia mearnsii. No affect of Acacia Mearnsii on ezyme indices suggest there was no physiological response to fatty acids within the muscle and fat. Calcium nitrate did not decrease SFA in SCF, IMF or rumen fluid (P>0.05), but CaN did decrease the SFA percent in IMF (P<0.05). Monounsaturated fatty acids increased as a percent in IMF and gravimetrically in PRF (P<0.05). Calcium nitrate did not affect PUFA in any of the fatty acid depots (P<0.05). The PUFA/SFA ratio only increased as a molar percent on IMF (P<0.05). There was no affect on any of the health indices in SCF or PRF (P>0.05). Calcium nitrate deceased the atherogenic and thrombogenic fatty acids in IMF resulting in a lower atherogenic index (AI) and thrombogenic index (TI) index (P<0.05 and P<0.001, respectively). Only the molar percent showed a higher hypocholesterolaemic fatty acid index (h) and lower hypercholestrolaemic fatty acid index (H; P<0.05). The h/H index was better in the CaN based diet (P<0.05). An increase in the delta-9 desaturase index suggests the lower percent and concentration of C18:0 in the CaN based diet (P<0.05). A change in the Vaccenic acid /stearic acid ratio in the rumen fluid of CaN supplemented lambs suggests that the microbes in the last step of biohydrogenation were affected by NPN source. Rams had a lower percent and gravimetric concentration of SFA in IMF and SCF. Monounsaturated fatty acid decreased as a gravimetric concentration in IMF and SCF (P<0.05). Polyunsaturated fatty acid increased as a percent in IMF, SCF and PRF and as a gravimetric concentration in PRF (P<0.05). The PUFA/SFA ratio was higher in all the fatty acid depots (P<0.05). The atherogenic and cholesterolaemic fatty acids decreased AI and H in all fatty acid depot sites (P<0.05). The desirable fatty acid index (DFA) was higher in ewe IMF, lower as a gravimetric concentration in SCF and increased in PRF as a percent (P<0.05). The molar percent h index was higher in IMF and SCF in ewe lambs but lower as a gravimetric concentration in rams (P<0.05). Sex affected the elongase index in IMF and PRF (P<0.05) and delta 9 desaturase activity in IMF, SCF and PRF (P<0.05). Weight did not affect the nutritional value of the fatty acid profile. There were no changes to the SFA, MUFA or PUFA percent or gravimetric concentrations (P>0.05). Of the individual important fatty acids, C16:0 was consistently lower as a percent and gravimetric concentration in lighter lambs in all the fatty acid depot sites. The elongase activity index suggests that elongase may have reduced C16:0 (P<0.05). The health indecis were not affected by weight (P>0.05). Rams were superior in both carcass characteristics and fatty acid profile. Weight affected CCW, EMA, SCF depth and individual fatty acids. This indicated the importance of the date and weight at which ewes and rams are slaughtered. Using condensed tannin and CaN (to reduce methane emissions in lamb) influenced some carcass characteristics and the fatty acid metabolism of lamb. Although tannin increased days on feed and decreased CCW and D%, and CaN decreased D%, overall, they can be recommended for their acceptable fatty acid profile.