SciELO - Scientific Electronic Library Online

 
vol.40 issue5 author indexsubject indexarticles search
Home Pagealphabetic serial listing  

South African Journal of Animal Science

Print version ISSN 0375-1589

S. Afr. j. anim. sci. vol.40 n.5 Pretoria Jan. 2010

 

The conversion of dopamine to epinephrine and nor-epinephrine is breed dependent

 

 

H.A. O'NeillI,#; E.C. WebbI; L. FrylinckII; P. StrydomII

IDepartment of Animal and Wildlife Sciences, University of Pretoria, South Africa
IIAgricultural Research Council, South Africa

 

 


ABSTRACT

In previous reports, Nguni type cattle have shown to have a lower glycolytic potential with less glycogen measured in muscles 1 h post-mortem. With the release of catecholamines in the immediate pre-slaughter period, there is potential for depletion of muscle glycogen, because of the fact that epinephrine activates muscle adenylate cyclase and thereby stimulates glycogen breakdown. Epinephrine and nor-epinephrine are secreted as a result of any "fight or flight" situation. Tyrosine is a conditionally non-essential large neutral amino acid and the precursor of the neurotransmitters dopamine, nor-epinephrine and epinephrine. Ante-mortem stress experienced by an animal may be influenced by amino acids that provide substrates for neurotransmitter synthesis. The Nguni type cattle showed 55.8% and 55.1% greater urinary nor-epinephrine values than for the Brahman- and Simmental type cattle respectively. The Nguni type cattle showed 35.6% and 43.8% greater urinary epinephrine values than the Brahman- and Simmental type cattle respectively. The higher urinary nor-epinephrine and epinephrine levels measured in Nguni type cattle could either be explained by a greater neuronal out flux immediately prior to slaughter or a slower re-uptake.

Keywords: Meat tenderness, urinary catecholamines, beef breeds, dopamine


 

 

Introduction

Domestic animals destined to be slaughtered are exposed to various stressors in the ante-mortem environment. These stressors include transport, handling, mixing and time of feed and water. These events stimulate the hypothalamic-pituitary-adrenal axis to drive a number of physiological changes such as energy depletion. These physiological changes have an economic impact on carcass yield and meat quality. Nutritional supplementation during the ante-mortem period may be effective in attenuating these conditions, thereby improving animal welfare, carcass yield, and meat quality (Schaefer et al., 2001).

 

Figure 1

 

Ante-mortem stress experienced by an animal may be influenced by amino acids that provide substrates for neurotransmitter synthesis. Tyrosine is a conditionally nonessential large neutral amino acid. Tyrosine is the precursor of the neurotransmitters dopamine (DA), nor-epinephrine (NE) and epinephrine (E) (D'Mello, 2003).

Exposure to stress increases the utilization and synthesis of DA, NE and E; the availability of tyrosine for catecholamine (CAT) synthesis can become rate-limiting under these conditions (Schaefer et al., 2001).

When CAT synthesis is compromised, animals become less resistant to stress, developing an array of counterproductive behavioural (learned helplessness) and physiological changes. These animals are unable to respond appropriately to stimuli and are unable to function normally, to the extent that even eating and sleeping are disturbed (Anisman & Zacharko, 1986; Lieberman, 1994).

 

Methods and Materials

One-hundred-and-eighty animals were slaughtered at the specified A-age (no permanent incisors) and fatness-class 2 - 3 (5 - 7 mm subcutaneous fat thickness). Sixty Brahman type (Bh-x), 60 Simmental type (Sm-x) and sixty Nguni type (Ng-x) crosses were used. The animals were slaughtered at the ARC-Irene abattoir. CAT's were measured in urine samples that were collected from the bladder with a syringe and needle approximately 12 minutes post-mortem, immediately after evisceration. Urine samples were preserved as described by Lowe et al. (2000) and analysed by HPLC-method as described by Gouarne et al. (2004). Concentrations of CATs are volume related and for this reason only creatinine corrected CAT concentrations were considered in the statistical analysis. Samples of the m. longissimus (20 g) were taken at one hour post-mortem and covered with aluminium foil, frozen in liquid nitrogen and then ultra frozen for the determination of energy values, e.g. glucose, glycogen and ATP-6-P.

 

Results and Discussion

Nguni type cattle had 55.8% (P <0.05) and 55.1% (P <0.05) greater urinary NE and 35.6% (P <0.05) and 43.8% (P <0.05) greater urinary E values than Brahman and Simmental type cattle which can either be explained a greater neuronal out flux immediately prior to slaughter or a slower re-uptake. Interestingly, from O'Neill et al. (2008), Nguni type cattle had a smaller glycolytic potential with less glycogen measured in muscles one hour post-mortem.

 

Table 1

 

Conclusion

Evidence shows clearly that Nguni type cattle have a greater catecholamine conversion rate to NE and E. Linked with this was the finding that Nguni type cattle have a smaller glycolytic potential than the Brahman- and Simmental type cattle. Therefore one can conclude that Nguni type cattle are genetically predisposed for a higher NE and E conversion rate with a subsequent lower glycolytic potential in the muscle.

 

References

Anisman, H. & Zacharko. R.M., 1986. Behavioural and neurochemical consequences associated with stressors. Ann. N.Y. Acad. Sci. 467, 205-225.         [ Links ]

D'Mello, J.P.F., 2003. An Outline of Pathways in Amino Acid Metabolism. In: Amino Acids in Animal Nutrition (2nd ed.). Ed. D'Mello, J.P.F., Edinburgh, UK CAB International.         [ Links ]

Gouarne, C., Foury, A. & Duclos, M., 2004. Critical study of common conditions of storage of glucocorticoids and catecholamines in 24-h urine collected during resting and exercising conditions. Clinica Chimica Acta. 348, 207-214.         [ Links ]

Lieberman, H.R., 1994. Tyrosine and stress: human and animal studies. In: Food Components to Enhance Performance. Ed. Marriott, B.M., National Academy Press, Washington, D.C., USA. pp. 277-299. (Quoted by Schaefer et al., 2001).         [ Links ]

Lowe, T.E., Devine, C.E., Wells, R.W. & Lynch, L.L., 2003. The relationship between postmortem urinary catecholamines, meat ultimate pH, and shear force in bulls and cows. Meat Sci. 67, 251-260.         [ Links ]

O'Neill, H.A., Webb, E.C., Frylinck, L. & Strydom, P., 2008. The energy status, ultimate pH and colour of post-mortem muscle of three different beef breed types. 54th International Congress on Meat Science and Technology, South Africa, Cape Town.s        [ Links ]

Schaefer, A.L., Dubeski, P.L., Aalhus, J.L. & Tong, A.K.W., 2001. Role of nutrition in reducing ante-mortem stress and meat quality aberrations. J. Anim. Sci. 79, E91-E101.s        [ Links ]

 

 

# Corresponding author. E-mail: adri.oneill@up.ac.za