Changes in muscle glycogen in sheep with low levels of basal glycogen fed two levels of metabolisable energy.

Abstract

8A Changes in muscle glycogen in sheep with low levels of basal glycogen fed two levels of metabolisable energy R. Jacob1, D.W. Pethick1, D. Masters2 and J. Milton 1 2 3 3 School of Veterinary and Biomedical Science, Murdoch University, Murdoch WA 6150 CCMAR, CSIRO, Floreat Park WA 6014 University of Western Australia, Nedlands WA 6009 jacobsj@wfag.agvic.gov.au Low muscle glycogen before slaughter results in meat with a high ultimate pH (pHu) (Warriss 2000). Meat with a pHu above 5.7 tends to be dark, has reduced shelf life, lower yield, stronger flavour, and is less attractive to consumers, and is less tender in the range 5.7 to 6.2. Pethick and Rowe (1996) demonstrated a positive linear relationship between metabolizable energy (ME) intake over 60 d of sheep and their basal muscle glycogen. The aim of this study was to measure the change in muscle glycogen from a low basal level in sheep fed two different levels of ME. Muscle glycogen was measured in M. semimembranosus on four occasions over a 28 day period in full wool, 12_month old Merino wethers fed two levels of a pelleted ration. For the low ME treatment, the pellets were fed at a maintenance level whilst for the high ME treatment they were fed ad libitum. To avoid acidosis, the ration was restricted in both groups for the first 5 days of the experimental period. Prior to the experiment sheep were offered wheaten hay (7.7 MJ ME/kg DM) at the rate of 1.3 kg DM/sheep/ day but hay residues were not measured. Sheep were fed in small paddocks in groups of 7, replicated 3 times for each treatment. The pelleted diet contained 10.6 MJ ME/kg, 23.8% acid detergent fibre, and 14.5% crude protein (DM basis). It was made from lupin seed, cereal hay and straw, wheat grain, expeller canola meal, a mix of macro and trace minerals, vitamins and lasalocid (30 mg/kg as fed). Muscle samples were taken from live animals with a biopsy technique using local anaesthetic. Muscle glycogen increased to a maximum at 7 d then decreased to a new apparent basal level 14 d after the pelleted diet was offered to each group. The magnitude of the increase in muscle glycogen for the low ME group was larger than expected and the reasons for this are not clear. These results suggest that feeding a concentrated diet to increase muscle glycogen in young sheep need only be continued for 7_14 d, if that is its sole purpose. High ME diets will result in higher muscle glycogen than low ME diets within such a time frame. Pethick, D.W. and Rowe, J.B. (1996). The effect of nutrition and exercise on carcass parameters and the level of glycogen in skeletal muscle of Merino sheep. Australian Journal of Agricultural Research 47, 525_537. Warriss, P. (2000). Meat Science. An Introductory Text. CAB International, Wallingford, Oxon, UK. Table 1 Glycogen in the M. semimembranosus of sheep with low and high metabolizable energy intakes. Mean daily ME intake (MJ/sheep/day) 8.7 � 0.160 14.3 � 0.370 Muscle glycogen (g/100g) Day 0 0.89 � 0.053a 0.89 � 0.050a Day 7 1.74 � 0.068 2.26 � 0.120 b b Group Low ME High ME Day 14 1.25 � 0.047 1.62 � 0.099 c c Day 28 1.31 � 0.062 1.44 � 0.068 c c Significance ** ** Values are means � SEM Significance: ** P<0.01; a,b,c values not having the same superscript in a row are significantly different Recent Advances in Animal Nutrition in Australia, Volume 13 (2001)