What are the effects of various intercrops on the feed utilisation and milk production of dairy cows? And what is the best strategy for optimising intercropping systems? What is their economic impact? Let’s discuss these issues.
Intercropping is a husbandry system by which different crops are grown at the same time on the same area of land. The system has been practised in many parts of the world in a variety of ways, depending on the producer’s need, i.e., hay, silage, grazing, or green chop.
As an agricultural practice, intercropping promotes yield stability because not all the crops in a mixed cropping system are likely to be equally affected by variations in weather conditions. Crops with different growth habits may also vary in their environmental requirements, leading to complementary canopies and root systems. In some instances, they are able to exploit light, nutrients, and water more fully than monocultures.
By intercropping soybeans with maize, for example, the mixture will be higher in crude protein (10-11% CP for maize-soybean intercrop vs. 8% CP for maize monoculture). The intercrop will also deliver higher lysine and methionine values (219%) than maize monoculture. The increased production of quality protein and essential amino acids achieved by intercropping is of special importance in the nutrition of all classes of farm animals, including ruminants.
Ruminants less sensitive to protein quality
Although ruminant animals are thought to be less sensitive to protein quality and are able to overcome a dietary deficiency of essential amino acids such as lysine and methionine by synthesising these acids in the rumen, evidence with high-producing animals, particularly dairy cows, suggests that optimum productivity cannot be obtained by feeding low-quality protein diets. This may be particularly true in areas known to be protein-deficient, such as many tropical and subtropical regions.
Greatest potential for intercropping
The greatest potential for intercropping is in these areas. In terms of mineral content, maize-soybean intercrops were found to be higher in calcium (0.7-0.8% vs. 0.2% for maize). The phosphorus level of maize-soybean silage was slightly higher than for maize silage alone, but the higher calcium level delivers a ratio of 2:1 Ca:P, which is desirable for lactating cows. Planting soybean together with maize for silage will thus improve the protein and mineral content and will require less protein and mineral supplementation to meet the requirements of dairy cows, and so will deliver an economic advantage in the feeding programme.
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With most intercropping systems, no differences in feed intake were noted, except in cases where the intercrops were preserved as silage. Intake may be reduced here to a varying extent, depending mainly on the crop variety and the pre-ensiling treatment used.
In one study:
The silage intake (kg dry matter per day) of dairy cows was 9.2 with grass silage and was reduced to 7.1 when grass silage was replaced by pea-barley intercrop silage. The low intake in the latter case was mainly attributed to the fermentation characteristics of the pea-barley intercrop and the formation of excessive amounts of lactic acid and ammonia, which adversely affect silage intake. Increasing the dry matter content of the silage raw material by wilting or by reducing the pea-to-cereal ratio appears to be beneficial in terms of ensiling quality.
In a study on intercropped grass-alfalfa as silage for dairy cattle, the dry matter and protein digestibility of the intercropped silage were improved compared to alfalfa silage alone. The improved digestibility in this case was the result of the following reasons:
The rumen microbiome’s role in increasing animal efficiency
The demand for more animal protein, especially from ruminants, must be met using less land, water and with a significant reduction in the environmental footprint of livestock production systems.
It has been reported by researchers that feeding pea-wheat intercrop silage instead of grass silage reduced the concentrate requirement for dairy cows by 60% without adversely affecting milk yields or quality (Table 1). This is why pea-wheat intercrops may be a viable cost-saving option for dairy farmers. The study also demonstrated the importance of using a short rather than a long-straw pea variety in the intercrop. The use of shorter-straw pea minimises shading of the companion crop. This, in turn, allows a greater capacity of the latter to restore its nutrients through photosynthesis and hence improves its contribution to the crop mixture, with a resulting improvement in milk production.
Often components in intercrop communities may compete with each other for environmental resources. Dominance may occur with either crop, depending on the species, plant height, the interaction between resources under different cropping situations, and the specific nutrient/water requirements at different stages of development. Minimising competition between intercrops should be the main objective in the management of such systems. Proper cultivar selection, appropriate spatial arrangement, and adequate water supply all help alleviate competition effects and enable the maximum benefits of intercrops as feed sources for livestock to be achieved.
References are available from the author upon request.