Grazing crops with cattle

DAFWA research: Cattle performance grazing canola and cereal crops

Cattle grazing cereal crops had a higher liveweight gain compared to the cattle that remained on the pasture. However to see a significant benefit from grazing dual purpose crops, the grazing period may need to be longer than four weeks particularly when grazing canola. The highest growth rates for cattle grazing the cereal crops were achieved when the stocking density was 12 DSE/ha. The growth rate reduced as the stocking density was increased.

Aims

To investigate and demonstrate the performance of cattle grazing canola and cereal compared to animals left on pasture.

To investigate the value of spelling the pasture during the time the cattle are grazing crops.

Method

The performance of yearling cattle grazing crops for four weeks during winter was investigated in an experiment conducted at the Esperance Downs Research Station. This experiment was conducted in conjunction with an experiment assessing the impact of grazing, by cattle, on a range of varieties of canola, wheat and barley.

Twenty seven yearling heifers aged approximately 15 months with an average weight of 344kg commenced the experiment grazing pasture at a stocking rate of 9DSE per hectare. The heifers were then divided into three treatments; remaining on pasture (control), grazing canola or grazing cereals (a combination of predominantly wheat with some barley variety plots). Grazing of the cereals and canola commenced on 15 June for four weeks. Following this four week crop grazing period the cattle from the two cropping treatments returned to their pasture plots for an additional nine weeks until all treatment animals were slaughtered on 26 September.

Stocking rates during the four week crop grazing period varied from 12–30 DSE/ha as the grazing area available was manipulated to ensure adequate grazing pressure. The average stocking rate was 22DSE/ha for cereals and 20DSE/ha for canola.

Before being introduced to the canola and cereal crops the heifers were yarded for six hours and fed hay ad libitum to assist their introduction to the crop species. All treatments had access to hay during the four week grazing period at the rate of 1.5kg per head per day (hd/day). In addition the cattle in all treatments had access to a mineral lick supplement (Econovite™) for the four week grazing period.

During the 13 week period the cattle were weighed and assessed fortnightly for fat depth at the P8 site. The pasture plots were assessed fortnightly for feed on offer (FOO) (kg DM/ha) and botanical composition was assessed three times during the 13 week period. Both the FOO and the botanical composition were used to determine the impact of spelling pastures while the cattle were grazing crops.

Results

Liveweight gain

The liveweight gain of the cattle grazing the cereal crop was higher than that of the cattle grazing either the canola or pasture for the four week grazing period (Figure 1). The difference in liveweight carried through until the end of the experiment. However the only significant liveweight difference at the end of the experiment was between the animals that had grazed the cereal crops and the control animals that had remained on pasture for the entire thirteen weeks (Table 1). The growth rate of the cattle grazing the canola crop for the first two weeks was extremely low (0.04 kg/hd/day) as the animals adapted to the canola crop. However their growth rate improved (0.89 kg/hd/day) during the second fortnight of the four week period and was the highest of the three treatments for this two week period.

Figure 1 Average liveweight of the heifers during the three treatments - cereal (■), pasture (O) and canola (▲) for the 13 weeks of grazing including the four week period of crop grazing.

The cattle grazing the cereal responded well in the first fortnight of the four week grazing period achieving a growth rate of 1.41kg/hd/day. This growth decreased in the second fortnight to 0.67kg/hd/day as the grazing area was reduced to increase the grazing pressure on the experimental plots.

Final value of the cattle

Although the animals that grazed the cereal crops were significantly heavier at the end of the experiment compared to the control animals that remained on the pasture, this was not reflected in the carcass weights. The slightly higher average carcass weight seen in Table 1 for the cereal grazing treatment was not significantly different (P> 0.05) from the carcass weights of the other two treatments. This in turn meant that the difference in the average final value of the cattle from each treatment was also not significant.

Values with columns with different superscripts are significantly different at P ≤ 0.05

Value of the spelled pasture

The difference between the feed on offer for the pasture plots that were spelled while the cattle were grazing either the canola or cereal treatments compared to the control treatment can be seen in Figure 2. At the end of the four week period the feed on offer difference between the spelled pasture plots and the grazed plots was only slightly higher at 120kg of dry matter per hectare, which was not significant. The difference in feed on offer became even less as the cattle grazed the pasture plots for the remaining nine weeks.

Figure 2 Average FOO of the pasture for the three treatments and rainfall (bars) for the 13 week grazing period including the four week crop grazing period cereal (■) canola (▲) and pasture (O).

Conclusion

The lack of a significant difference between the final average dollar values of the cattle from the three treatments relates to the inherent variability of the dressing percentages of the cattle within each treatment. This may be overcome if the animals were grazed on the crops for longer than four weeks, particularly canola. It took two weeks for the cattle grazing canola to adapt to the change in diet (reflected in the poor growth rate) and they only benefited from the two weeks following this adaptation period. The results suggest that to achieve a benefit from grazing canola the grazing period should be greater than four weeks to overcome this poorer performance during the first two weeks.

The reduction in growth rate of the cattle grazing the cereal crop during the second two weeks of the four week grazing period corresponded to the increase in stocking density for this period. The stocking density was increased to impose adequate grazing pressure on the trial plots of the variety trial component of this experiment. This forced the cattle to consume more of the stem component of the cereal plants, leading to a reduction in the quality of the feed consumed. Higher growth rates in growing cattle grazing cereal crops may be achieved at low stocking densities where less of the total crop biomass is consumed.