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Unit 1 - What's in it for me?
Unit 2 - Saltland Basics
Unit 3 - Can I trust the technology?
Unit 4 - Plant and animal performance
Unit 5 - Sheep, cattle and conservation
Unit 6 - Do the $$$'s stack up?
Unit 7 - The saltland toolbox
Site Assessment
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UNIT 4

Plant and animal performance

 

4.5  Animal performance 

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Animal nutrition

As with production from saltland pastures, there are now numerous examples from research and farmer experience showing that animals can be successfully grazed on saltland pastures. Key conclusions from the SGSL program were:

  1. Depending on the time of year and time after revegetation, salt-tolerant shrubs and pastures generally resulted in significant increases in animal production per hectare, measured as metabolisable energy utilisation (MEU). The increases were due mainly to higher carrying capacity with increased vegetative dry matter production rather than improved per-head performance.
     
  2. The nutritive value of sown perennial pasture species that grew well on the saline sites (e.g. puccinellia and tall wheatgrass) were not significantly better than most dominant edible volunteer species, highlighting the need for breeding and selecting a greater range of suitable candidate species. The exception was balansa clover (an annual legume) which had high digestibility and can be successfully grown at locations with low winter soil salinity and moderate waterlogging.
     
  3. From a wide range of species sown, the species which survived and contributed significantly to the improved carrying capacity and animal performance in saline conditions were quite limited and included saltbush, puccinellia, tall wheatgrass, and balansa clover in limited situations.
     
  4. With the exception of puccinellia and balansa clover there were no species with high salt and waterlogging tolerance that stood out as having a high nutritive value. Grazed as a monoculture, livestock would not perform as well on saltland pastures as they would on pastures of most vegetative non-saline species in a similar location. Poorer production can be attributed to the low energy value of many saltland pasture species, the energy cost of excreting salt from the body, the decrease in organic matter digestibility with high salt intakes, and the suppression of appetite. In addition, there are secondary compounds (such as betaine, tannins, coumarin, oxalates and nitrates) that can help plants survive inhospitable conditions but which can be detrimental to grazing animals and/or affect palatability.
     
  5. The halophytes have higher concentrations of crude protein (CP) than perennial grasses, and about the same level as annual grasses/legumes and so could provide a valuable source of CP and vitamin E at times when green feed is in short supply.
     
  6. The salt content of halophytes is limits the voluntary intake of sheep and cattle, and the high levels of S and nitrates in some halophytes may limit intake and potentially lead to animal health problems.
     
  7. The salt-tolerant perennial grasses tended to have lower nutritive value than most current agriculturally important annual grasses and legumes. This reflected the low nutrition levels of the saline land and also the seasonal grazing regime. While this may highlight an opportunity for breeding and selecting a greater range of species, such effort is unlikely.
     
  8. Related work shows that the efficiency of wool growth increases per unit of digestible organic matter intake on diets containing salt when tested in an animal house.
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Diet Selection

Grazing animals have the ability to select a diet that is matched to their nutritional needs if they have the opportunity.
Research in the SGSL program showed that the diet selected by the sheep grazing rows of saltbush with an annual under-storey changed throughout the year in response to the changing quantity and quality of the saltbush and under-storey – see Figure 4.7.

Figure 4.7

Figure 4.7. Saltbush selection by sheep (as a proportion of total diet) compared to the digestibility of the legume based under-storey in each season.

In autumn, the sheep had to choose between two alternative forages with equally poor energy values – saltbush and dead/dry under-storey, and consequently selected about 50% saltbush and 50% of the dry under-storey as their diet.

In spring, when the under-storey is highly digestible and in plentiful supply, the sheep ate predominantly under-storey. Interestingly, however, they still included an average of 11% saltbush in their diets.

In winter the under-storey was of high quality but in short supply, so the sheep selected a diet that included 25% saltbush.

These outcomes support animal house trials where sheep fed high salt diets with a range of low salt alternatives chose to eat some of the high-salt feed, even when a high-energy, low-salt alternative was offered. Presumably the sheep were supplementing themselves with minerals or secondary compounds by eating the saltbush

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