Pre-slaughter administration of glycerol as carbohydrate precursor and osmotic agent to improve carcass and beef quality
Introduction
Recent interest in biodiesel as a renewable energy resource has led to the production of large amounts of glycerol as a by-product. Several studies have identified animal feed as a possible use for unrefined glycerol (Della Casa et al., 2009, Lammers et al., 2008, Parsons et al., 2009), since the molecule may be converted into glucose (Mach et al., 2009). Glycerol is converted to propionate in the rumen (Mach et al., 2009), which is transformed into glucose and provide energy through the gluconeogenic pathway, and then is converted into glycogen in the liver. Glycogen is used as a substrate for postmortem lactic acid production in muscle and therefore the pH falls (Immonen and Puolanne, 2000). So it can produce sufficient pH decrease to reach the target value (=below 5.8) after slaughter, contributing to the prevention of Dry Firm Dark (DFD) meat, which causes substantial economic losses in the beef meat mark (Brandon, 2004). Indeed, some Spanish meat industries penalise carcass price with discounts of 30% when meat pH measured 24 h after slaughter is greater than 5.8 (Mach et al., 2008a). Previously, it was studied the administration of other substances previous slaughter, e.g. sorbitol, to prevent the incidence of this defect on meat (Bignon, 1992). Glycerol supplementation might therefore be considered for preventing the pH of beef from exceeding 5.8. Furthermore, osmotic properties have been attributed to glycerol (Parker et al., 2007). Research in human has shown that glycerol included in sports soft drinks increases water retention in high-performance athletes (Anderson et al., 2001, Wagner, 1999). The ingestion of this type of drink before exercise results in hyperhydration of the body cells so, in a parallel way, it could maintain body water content in stress situations, such as long distance transport (Parker et al., 2007), by which contributes to prevent water losses in meat, while improving some quality attributes like juiciness and tenderness (Offer and Knight, 1988).
In Bos indicus steers, Parker et al. (2007) concluded that glycerol administration at 2 g kg−1 body weight (BW) before transport in a single dose, shows promise as a prophylactic treatment for attenuating the effects of long distance transportation by maintaining body water, decreasing the energy deficit and preserving health and muscle quality. However, the authors did not study the effect of glycerol on carcass or beef quality.
The hypothesis of this study was based on the glycerol role as carbohydrate precursor and osmotic molecule that could improve carcass and meat quality. Due to nasogastric tube administration is not a farm practice; administration in drinking water will be studied as an alternative. Higher levels of glucose in blood might be expected in the glycerol groups, because between 80% and 90% of glycerol is fermented in the rumen and provides propionate as a glucose precursor (Ramos and Kerley, 2012), so blood analyses were carried out. In addition, as glucose could be transformed into glycogen in liver and muscle, glycogen content was measured. Then, to evaluate the transport as stress situation, other parameters, as cortisol were studied. So, the aims of this research were to study the effect of pre-slaughter glycerol administration by nasogastric tube or in drinking water on plasma parameters, liver glycogen levels, carcass parameters and beef quality in young bulls.
Section snippets
Animals and dietary treatments
All procedures involving animals were approved by the University of Murcia Ethics Committee, and the animal care and experimental procedures used in this study conform to national and EU regulations and guidelines (EU Directive 86/609, as modified by Directive 2003/65, OJEU, 2003), concerning the protection of animals used for scientific research. The crude glycerine obtained from biodiesel production had the following chemical composition: 86.6% glycerol, 7.50% moisture, 5.88% ash, 3.06%
Blood parameters and liver glycogen
Table 1 shows plasma parameters in bulls before treatment and in the abattoir. Glucose concentrations were increased similarly (P<0.001) in all groups following transport. Other studies have also noted increased glucose levels after transport (Cafazzo et al., 2012, Tadich et al., 2005). This is because in a stress situation, such as transport, the activity of the sympathetic nervous system is increased, which increases glycogen breakdown and gluconeogenesis in the liver, leading to an elevated
Conclusion
Glycerol administration 24 h before slaughter did not affect the blood parameters modified by transport stress, carcass quality or the pH of meat. However, it seems beef WHC was improved, without modifying the sensory quality of the resulting cooked meat, although sodium effect is not clearly, and must be studied. Glycerol given by nasogastric tube or in driking water seems to have similar effects, however, it could be interesting to study in depth the effect of glycerol on meat WHC, for example
Conflict of interest
The authors of the article “Pre-slaughter administration of glycerol as carbohydrate precursor and osmotic agent to improve carcass and beef quality” and authors M. Egea, M.B. Linares, F. Hernández, J. Madrid and M.D. Garrido declare no conflict of interest to the publication of the article.
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