Forage halophytes such as saltbush (Atriplex spp) are being widely used to revegetate Australian
saline land and can also provide a medium quality fodder source. There is widespread anecdotal
evidence that sheep grazing on saltbush are leaner, tastier and juicer. This thesis investigated the
potential to produce a high quality carcass with improved eating quality from grazing sheep on
saltbush on saline land.
The first experimental chapter in this thesis details an animal house experiment investigating the
carcass, eating and wool quality and physiological responses of sheep ingesting a 60:40 dried
saltbush (Atriplex nummularia):barley grain (S+B), ration verses a 33:25:42 lupin grain:barley
grain:oaten hay ration (Control, C) for 10 weeks prior to commercial slaughter (Chapter 4).
Subsequently, two field experiments were conducted to examine the effects of grazing saltbush
on saline land compared to dry senesced pasture on carcass and eating quality of lambs
(Goomalling 2003) and hoggets (Wickepin 2004) (both chapter 6) for 14 weeks. Both chapters
demonstrated that the ingestion of saltbush resulted in significantly less fat and in the 2 field
experiments the ingestion of saltbush resulted in more lean on the carcass compared to sheep
grazing a stubble/pasture (control) ration. These are positive findings for processors as costs of
fat denudation are high so the lower the fat content and for farmers because less fat is deposited
on the carcass per unit of liveweight gain. The decreased deposition of fat was attributed to the
higher protein:energy ratio available for production, secondary compounds in saltbush and lower
circulating insulin and higher growth hormone of the S+B fed sheep compared to the control fed
sheep. Further work is needed to determine if these beneficial improvements in carcass
composition can be achieved without compromising animal production. The long term grazing of
saltbush did not result in commercially desirable hot carcass weights unless the sheep were supplemented with a high energy source such as barley. The low growth rates are attributed to a
decreased availability of energy substrates, low feed intake and increased energy output of sheep
fed high salt diets. The low energy intake of the S+B fed sheep also resulted in an a significantly
lower percentage of unsaturated fat and unchanged levels of saturated fat in the fat depots
compared to the C treatment.
Consumer taste tests conducted on meat from experiments in both chapter 4 and 6 indicated no
difference between the treatments for any of the eating quality traits assessed. This can be
considered a positive result as sheep can be finished on saltbush without any detriment to eating
quality. High vitamin E levels in the meat may have also prevented the development of rancid
flavours and aroma. It can be speculated that saltbush does not impart beneficial flavour and
aroma volatiles as previously thought; instead the high vitamin E levels inhibit off-flavour and
aroma development compared to meat from sheep grazed on dry pasture.
The long term ingestion of saltbush also resulted in significantly lower urine specific gravity
(USG), muscle dry matter and higher urine weights suggesting that the saltbush fed sheep had a
better hydration status compared to control fed sheep. However, this finding did not correspond
with higher hot carcass weight or dressing percentages. The increases in muscle fluid content of
the saltbush fed sheep were attributed to changes in body composition. The saltbush fed sheep
had a higher lean and lower fat content which corresponded with a greater body fluid content as
found in the animal house study.
Under conditions where the body composition of sheep remains the same, the use of short term
strategic feeding of components of saltbush was investigated (mimicked in the form of salt and
betaine) to reduce dehydration and subsequent reductions in carcass weight and dressing percentages (Chapter 7). Salt and or betaine were fed for 1 week either prior to a 48 h period of
water deprivation or prior to 48 h commercial slaughter process where water was available in
lairage from 24-48 h. Under both scenarios the diets did not result in improved dressing
percentages, hot carcass weights, muscle dry matter or muscle weights. The ingestion of high salt
diet prior to slaughter, did increase fluid retention in the extracellular spaces prior to slaughter
however by 48 h both groups were at a similar physiological and therefore similar hydration
status. Therefore similar levels of fluid were present in the muscles and no difference in carcass
weight or dressing percentage could be expected. An important observation from the second
experiment was that the high salt group drunk more water than the low salt fed sheep but the low
salt group consumed fluid in lairage also. The low salt fed sheep may have been encouraged to
drink water after observing the frequent drinking patterns of the high salt group.
This thesis has also shown that saltbush contains high levels of vitamin E (á-tocopherol) (193
mg/kg dry matter). As a result the concentration of á-tocopherol in plasma, liver and muscle of
the saltbush fed sheep was elevated compared to those grazing dry pasture. The high muscle
concentrations of vitamin E in the saltbush-grazed sheep resulted in improved meat colour
stability. The high vitamin E levels did not influence the drip and cooking loss of the meat
despite a decrease in the muscle dry matter of the meat. The browning of meat and increased drip
loss results in large losses to the meat industry due to value deterioration at the supermarket.
There is also great potential for the high vitamin E content in saltbush to be used for the
prevention of nutritional myopathy instead of using expensive and labour intensive synthetic
supplements.
In conclusion, this thesis has provided an insight into the carcass and eating quality of sheep
grazed on saltbush based saline pasture systems. The most significant findings were that
| Identifer | oai:union.ndltd.org:ADTP/221846 |
| Date | January 2006 |
| Creators | k.pearce@murdoch.edu.au, Kelly L Pearce |
| Publisher | Murdoch University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.murdoch.edu.au/goto/CopyrightNotice, Copyright Kelly L Pearce |
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