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- Plantain, if maintained at 60% in a pasture mixture, can improve forage quality and milk production.
- A kikuyu-ryegrass pasture see-saws dramatically between ryegrass dominating in winter and kikuyu dominating in summer, even if a perennial ryegrass is planted.
- The strongest driver of milk yield in this system was metabolisable energy content (ME), while NFC and NDF also played a role.
- Plantain can also play a role in stimulating intake in a pasture system, as it was associated with lowered NDF (fibre) content and higher potential DM intakes.
- Relative to kikuyu-ryegrass, alternative pasture mixtures such as the ones discussed here, hold the potential to increase quality of pastures grazed by our dairy cows, and in turn improve milk yield.
Plantain, if maintained at 60% in a pasture mixture, can improve forage quality and milk production. This was one of the primary findings from a dairy pasture system trial conducted at the Western Cape Department of Agriculture’s Outeniqua Research Farm.
The trial, in which four different pasture types were evaluated, was aimed at determining whether plantain, chicory and tall fescue could form the basis of alternative pasture systems to traditional kikuyu and ryegrass pastures. As expected, the cows grazing the kikuyu-ryegrass pasture had lower milk yields from late spring through to autumn than the fescue/plantain/red clover mixture, fescue + plantain monocultures, and chicory/lucerne/ryegrass mixture. But what were the main drivers of this trend?
The pasture see-saw
A kikuyu-ryegrass pasture see-saws dramatically between ryegrass dominating in winter and kikuyu dominating in summer, even if a perennial ryegrass is planted. Forage quality, and as result milk yield, shows the same dramatic pattern.
Non-fibre carbohydrate (NFC) content gives an indication of how much starch, sugars and pectin, all important for energy to produce milk, are present in a pasture. When ryegrass was the main component, NFC tended to be high, while it decreased as the kikuyu increased in the pasture. Neutral detergent fibre (NDF) followed the opposite pattern, increasing to well above 55% during summer when kikuyu dominated.
The most worrying aspect of this system, however, was that dry matter (DM) intake potential often fell so low in the summer that one would struggle to get enough pasture into the dairy cow to meet her needs. These results once again highlight how poorly suited kikuyu is for producing milk (Figure 1).
Figure 1: Milk yield of cows grazing different mixtures showed that forage herb based pastures had higher summer and autumn yields, but that once kikuyu invades it, this effect is lost.
The good news is that data also showed that the alternative pasture species and mixtures could address some of these issues. Both pasture mixtures containing a combination of legumes, forage herbs and temperate grasses had higher energy contents during summer and autumn for two years after they were established. The DM intake potential was also higher on alternative pasture mixtures throughout the study period.
As a result, the need for supplementing intake with other feed sources like concentrates, maize silage or hay, when supply is not limiting, would be reduced on forage herb based mixtures compared to kikuyu-ryegrass pasture. Fertiliser concentrates and purchased feeds are some of the greatest cost to producing milk from pasture, so this is an important finding.
Drivers of milk yield
Unfortunately, the study also made it clear that not all pasture mixtures, and their various components for that matter, are created equal. When trying to find the relationship between changes in pasture composition, forage quality and milk yield of the fescue/plantain/red clover mixture, only three parameters were found to be important.
The strongest driver of milk yield in this system was metabolisable energy content (ME), while NFC and NDF also played a role. The energy content was closely linked to the plantain content of the mixture, dropping below cow requirement once the plantain contributed less than 60% to the pasture make-up. In the same vein, energy content was severely negatively impacted when the pasture was invaded by weedy sub-tropical grasses such as Eragrostis plana, kikuyu and Paspalum (Figure 2).
Figure 2: Metabolisable energy content of different pasture mixtures.
Plantain can also play a role in stimulating intake in a pasture system, as it was associated with lowered NDF (fibre) content and higher potential DM intakes. In summer and autumn pastures, when intake and energy content often limits milk yield potential, plantain could be a game changer.
The dark horse of the study was the last mixture, based on chicory, lucerne and ryegrass, a popular choice among producers in the Western and Eastern Cape. There were no obvious patterns or correlations apparent at surface level. But what could be the cause of this? The current feeling is that the rapid changes in pasture composition (how much each component contributes to the sward) are to blame (Figure 3).
Figure 3: The only clear impact of pasture mixture on the crude protein content of pasture, is that lucerne in the chicory/lucerne/ryegrass mixture increased it.
This type of pasture quickly changes from ryegrass dominant in the winter after establishment, to chicory dominant in the first summer and then lucerne dominant in the second summer.
Prevent weedy grass invasions
Could the fact that the forage quality of all these components is relatively high mean that discerning which one is stimulating milk yield is close to impossible? Well yes, but the difficulty in determining true changes in composition in a mixture that is often very varied in composition on a paddock scale, could also play a role. The only clear answer that could be drawn from studying this mixture in regard to forage quality, is that the invasion of weedy grasses should be prevented at all costs.
Relative to kikuyu-ryegrass, alternative pasture mixtures such as the ones discussed here, hold the potential to increase quality of pastures grazed by our dairy cows, and in turn improve milk yield. However, the maintenance of a good composition, with few weedy grasses and the forage herbs as a major component, is a must. – Janke van der Colf, Outeniqua Research Farm, Western Cape Department of Agriculture
For more information, contact Janke van der Colf at email janke.vandercolf@westerncape.gov.za.
