Sorghum supplements for cows grazing temperate pastures

Date: 22 Sep 2004 Author: Brad Granzin

There is a considerable amount of ‘bad press’ stating that sorghum is a poor choice of grain to feed to grazing cows. From a scientific perspective, there is some justification for this, as sorghum has some strong physical barriers that make it hard for both the cow and the bugs in her rumen to digest it. Therefore adequate processing, such as fine rolling or hammermilling, is required to ensure proper sorghum digestion and to reduce grain loss in dung.

Research at Wollongbar

Despite this poor reputation of sorghum, recent research at Wollongbar Agricultural Research Institute has shown that sorghum supplements fed to cows grazing temperate pastures can produce similar milk yield and quality to that produced by cows on barley-based supplements.

The experiment

  • From early August to late October 2003, we fed 7 kg of concentrate based on either barley or sorghum (4 kg was fed at the am milking; 3 kg at the pm milking).
  • Both grains were fine rolled.
  • The energy content of barley was slightly lower than sorghum: 12.5 vs 13.2 MJ ME/kg DM (megajoules of metabolisable energy per kilogram dry matter). This is quite typical.
  • Apart from grain, each concentrate also contained sodium bicarbonate (buffer) and some other mineral supplements.
  • No protein supplements were fed.
  • There were 72 cows in the experiment (36 were fed barley; 36 were fed sorghum).
  • Cows grazed Matua prairie grass and Caversham biennial ryegrass pastures.
  • During the experiment, cows ate on average about 12.4 kg DM pasture per day. This did not differ between the two cow groups.

Results

The cows’ milk production and liveweight change during the experiment are given in Table 1.

  • Overall there was little difference in the milk yield and the protein content between the two groups.
  • Milk fat content was ‘statistically’ higher for sorghum. We think this was because the rumen is less disrupted by sorghum, as it is digested much more slowly than barley. (This is consistent with our earlier observations when we compared maize, another slowly digested grain, with barley. In that experiment, maize also caused higher milk fat concentrations - see Barley versus maize as supplements for grazing dairy cows.)
Table 1. A comparison of milk quality and liveweight for cows fed barley and sorghum grain-based supplements while grazing ryegrass and prairie grass pastures at Wollongbar
Milk and liveweight parameters Supplement grain base
BarleySorghum
Milk yield (L/cow/day) 28.2 28.1
Milk fat content (%) 3.4 3.5
Milk protein content (%) 3.1 3.1
Liveweight change (kg/cow/day) 0.65 0.68