Effect of Preslaughter Bull Handling on Ante Mortem Muscle Glycogen and Post Mortem pH and Glycogen Level (short communication)

Forty three bulls (13 Holstein, 12 crosses Holstein x Belgium Blue, 9 Slovak Pied and 9 crosses Slovak Pinzgauer x Piemontese) were taken in this experiment. Thirteen were stressed by mixing overnight before slaughter. Muscle values were analysed for glycogen ante mortem (M. semitendinosus), glycogen and pH post mortem (lh, 3h, 48h) from logissimus dorsi. The ante mortem and post mortem (lh, 3h) muscle glycogen concentration was depleted (P<0.01) in all stressed bulls. Differences (PO.01) were found also in pH (48h). Significant correlations (PO.01) between ante mortem and post mortem (lh, 3h) muscle glycogen respectivelly and ultimate pH supported the possibility to measure of stress and to predict carcass ultimate pH of bulls.


Introduction
Domestic animals often experience physiological insults when they are transported and handled.Transport and handling stress could reduce carcass yield, degrade well-being and meat quality.The impaet of transport and handling stress on meat quality variables including the rise of low glycogen meat and high pH occurence collectivelly reffered to as dark cutting or dark-firm-dry (DFD) meat (LACOURT and TARRANT, 1985;TARRANT, 1989;ZEMANOVA et al., 1987;MOJTO et al, 1991).Especially mixing of animals is known to contribute to dark cutting (LACOURT andTARRANT, 1985, SANZetal, 1996).
Ante mortem stress entails important modifications in post mortem biochemistry of muscle and meat quality.The major effect is exerted through its influence on mobilisation of musle glycogen stores.If these are reduced or depleted before or at slaughter the extent of post mortem acidification is consequently reduced (WARRIS, 1990;SANZ et al, 1996).Ultimate pH in post mortem bovine muscle may vary between 5.4 and 7.2, showing a direct relationship with stress intensity.The negative effect on meat characteristics of high ultimate pH caused by stress, due to mixing different male types of cattle, was recently clearly demonstrated (SANZ et al, 1996;BELTRAN etal, 1997).
The aim of this study was to examine the glycogen content ante mortem before slaughter and pH and glycogen level after slaughter of unstressed and stressed cattle beefs.

Animals. housing and slaughtering
The animals used in the experiment were 13 Holstein, 12 Holstein x Belgium blue, 9 Slovak bunt and 9 Slovak Pinzgauer x Piemontese bulls, weighing 550 kg.They were fed on supplemented forage diets.The animals (total 43) were tying housed and divided into the group A (n=30) tying housed and group B (n=13) loose housed (mixed) during night before slaughter.At the abattoir, the animals (group B) were kept overnight and had access to water but not food.Control (group A) and stressed animals (group B) were slaughtered at the Institute abattoir.

Sampling and analytical techniques
Just before slaughter, biopsy samples (approx.lg) of semitendinosus muscle (ST) were obtained using efficient non-stress spring loaded biopsy instrument (Biotech, Nitra).Samples of longissimus dorsi musle (LD) were also taken after slaughter (lh, 3h and 48h) directly frozen in liquid nitrogen for glycogen analyses (DREILING et al, 1987).pH was measured in the longissimus muscle (13th rib) using a probe type combined electrode and portable pH meter (Radelkis, Hungary).Differences between the means were assessed for Statistical significance using an unpaired Student t-test.Correlations between values were also calculated.

Results and Discussion
As follows from the results (Table 1) of glycogen level ante mortem (just before slaughter) and early post mortem (lh and 3h) we received significant differences (P<0.05) of glycogenolysis between the experimental groups.It was introduced (LACOURT and TARRANT, 1985) adrenalin release causes a general glycogenolytic response throughout the skeletal musculattire with glycogen depletion.Mixing of unfamiliar animals can precipitate such events as fighting and mounting and such activities deplete muscle glycogen, especially ofthe fast twitch fibers.In agreement with SANZ et al. (1996) our results supported the idea the main cause of lower glycogen level ante-and early post-mortem and higher ultimate pH (DC condition) was due to physical and emotional sfress of mixing unfamiliar bulls at abattoir overnight.Ante-mortem sfress entails important modifications in post-mortem biochemistry of muscle.If the muscle glycogen stores are reduced or depleted at slaughter the extent of post mortem acidification is consequently reduced (WARRIS, 1990).Ultimate pH in post-mortem bovine muscle may vary between 5.4 and 7.2' showing a direct relationship with sfress intensity (BELTRAN et al, 1997).As follows from our results (Table 2) we received significant (PO.01) correlation between glycogen level ante-and early post-mortem (lh, 3h) and ultimate pH (pH 48 ).
Correlations with three-hour post-mortem muscle pH (pH 3 ) were not significant (P>0.05).The results are in agreement with SHACKELFORD et al. (1994) they showed also lower correlations of pH 3 with pH u and tenderness and pH 3 was not enough effective in grouping stressed and unstressed animals in our experiment.In conclusion, the glycogen level ante-mortem (just before slaughter) and early postmortem (lh, 3h) was good predictor for assessing handling Stressors and carcass ultimate pH (pU^) of bulls.