Effects of pre-slaughter stress, sex and breed on blood stress indicators, heat shock proteins, glycolytic potential and lamb quality
- Authors: Stempa, Thuthuzelwa
- Date: 2019
- Subjects: Animal welfare , Meat--Quality
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/15376 , vital:40402
- Description: The main objective of this study was to determine the effects of pre-slaughter stress (transportation distance and lairage duration), sex and breed on blood stress indicators, heat shock proteins, post-mortem muscle metabolites (glycogen, glucose, glucose-6-phosphate and lactate), glycolytic potential and meat quality attributes from lambs slaughtered at a commercial abattoir. The study was conducted in a high-throughput commercial abattoir in the Buffalo City local municipality of the Eastern Cape Province, South Africa. A total of a hundred eight-month old Dorper and Merino lambs, both male and female, were used in the study. Blood samples for the analysis of glucose and lactate levels were collected using 10.0 mL disposable Becton Dickinson vacutainer tubes treated with fluoride oxalate (grey top) whereas those for determination of cortisol and heat shock protein 70 (HSPA1A) levels were collected using plasma separating vacutainer tubes (SSTTMII, gold top), and those for analysis of creatine kinase and lactate dehydrogenase were collected using 10.0 ml vacutainer tubes treated with Ethylenediaminetetraacetic acid (EDTA). Meat samples (~50 g) for the measurement of post-mortem energy metabolites (glycogen, lactate glucose-6-phosphate and glucose content) were collected from the Muscularis longimissius thoracis et lumborum (LTL) of each carcass ~30 minutes after slaughter and immediately frozen in liquid nitrogen (-196 oC) to prevent further glycolysis. Cold carcass weight (CCW), warm carcass weight (WCW) and carcass fatness (CF) was measured. Meat pH and temperature were measured at iii 45 minutes (initial pH), 6 hours and 24 hours ultimate pH (pHu) post-mortem. Meat colour coordinates [lightness (L*), redness (a*), yellowness (b*), hue angle (H*), chroma (C*)] were also measured 24 hours after slaughter. Furthermore, thawing loss (TL%), cooking loss (CL%) and warner braztler shear force (WBSF) was measured in the LTL 7 days post slaughter. Breed had a significant effect on plasma HSPA1A, plasma lactate, WCW, CCW, L*, muscle glycogen and WBSF. Sex had a significant effect on plasma HSPA1A and pHu. Pearson‘s correlations showed that meat muscle glycogen was positively correlated to glycolytic potential (P<0.001; r=0.63) and initial pH (P<0.05, r=0.20). Muscle lactate was positively correlated to muscle glucose (P<0.01, r=0.30) and glycolytic potential (P<0.001, r=0.79). A positive correlation was shown between muscle glucose and glycolytic potential (P<0.05, r=0.23). The level of LDH was affected by the distance travelled by lambs prior to slaughter. Lairage duration did not affect the levels of CK and LDH. Principal Component Analysis showed a relationship between distance travelled and CK and LDH; and that CK and LDH also influenced the quality of meat from lambs. With respect to sex and breed, the results indicate that female and Dorper were more stressed than male and Merino respectively. Muscle glycolytic potential and post-mortem metabolites have an impact on the quality of meat produced and the Merino had higher muscle glycogen levels at slaughter; hence they produced better meat quality compared to the Dorper. Moreover, no associations were seen between pHu and blood stress indicators. These results indicate that blood stress indicators at exsanguination cannot be used as useful indicators of dark cutting condition in lamb. A relationship between pHu, muscle glycogen and glycolytic potential was established and thus meat pHu can be used as a reliable indicator of tenderness in lamb.
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- Date Issued: 2019
Glycolytic potential and meat quality from dorper and merino sheep slaughtered at a commercial abattoir
- Authors: Stempa, Thuthuzelwa
- Date: 2015
- Subjects: Slaughtering and slaughter-houses Meat -- Quality
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/15310 , vital:40361
- Description: The objective of the study was to determine glycolytic potential and meat quality from Dorper and Merino sheep of both sexes slaughtered at a commercial abattoir. Dorper (n=52) and Merino (n= 48) breeds aged eight years, consisting of 50 intact rams and 50 non-pregnant ewes were used in the study. The sheep used in the study were reared, transported and lairised under identical conditions. Blood samples were collected at exsanguination for the measurement of glucose, lactate and cortisol levels. Samples were also collected from the Muscularis longmissius thoracis et lumborum (LTL) for the measurement glycogen, lactate levels, pH decline and colour. Correlations amongst blood stress indicators, muscle metabolites and meat quality attributes were also determined. Sex and breed had no effect on muscle glycolytic potential, glycogen and lactate levels from Dorper and Merino sheep of both sexes at the abattoir. Although sex and breed had an effect on pre-slaughter stress indicators (lactate and cortisol) collected at exsanguination. Ewes had higher levels of blood lactate (7.4 3 ± 0.49 mmol/L) and cortisol (293.92 ± 14.32 nmol/L) than the rams which had (5.19 ± 0.49 mmol/L) and (179.50 ± 14.32 nmol/L) lactate and cortisol levels, respectively. Furthermore, higher levels of lactate were observed in Dorper (7.54 ± 0.42 mmol/L) compared to the Merino sheep (4.97 ± 0.49 mmol/L). Meat pH decline and colour were also significantly affected by sex and breed. Ewes had higher levels of at pH45 minutes post slaughter (7.05 ± 0.04), pH3 hours (6.45 ± 0.04) , pH24 hours (6.00 ± 0.03), a* (14.31 ± 0.33) , b* (8.84 ± 0.29), H* (31.47 ± 0.73) and C* (16.75 ± 0.24) compared to the rams which had pH45 minutes (6.44 ± 0.04), pH3 hours (6.12 ± 0.04), pH24 hours (5.88 ± 0.03), a* (12.25 ± 0.33), b* (7.00 ± 0.29), H* (29.36 ± 0.73) and C* (14.15 ± 0.42) values. Moreover, Merino sheep had higher levels of L* (38.17 ± 0.48) and H* (31.59 ± 0.74) compared to the Dorper which had (36.39 ± 0.46) and (29.33 ± 0.71) L* and H* values, respectively. Blood cortisol was also positively correlated (P < 0.05) to glucose (r = 0.27), lactate (r = 0.37) but was negatively correlated (P < 0.001) to meat lightness (r = -0.44). Furthermore, blood cortisol was positively correlated (P < 0.001) to pH45 (r = 0.34), pH24 (r =0.22), meat yellowness (r = 0.24) and chroma (r = 0.37), but was negatively correlated to meat lightness (r = -0.47). Glycolytic potential was positively correlated (P < 0.001) to muscle glycogen levels (r = 0.66) and muscle lactate (r = 0.71).
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- Date Issued: 2015