Drought can cause many problems for farmers across Britain, when the hot weather pattern has broken, we are reminded of what rain is and its ability to grow grass. With this comes the possible problem of mineral deficiencies.
Of course, the quantity of minerals and trace elements in the grass does depend on soil type, botanical composition, fertilisation of the pasture and growth stage but weather conditions also affect this greatly.
Effects of long periods of droughts on soil
Prolonged periods of drought mean that soil moisture has been low, this will cause turmoil in mineral availability.
Low soil moisture will decrease soil microbe activity which plays an important role in breaking down organic matter and converting organic nitrogen(N) into inorganic nitrate nitrogen, this process is mineralisation.
Due to dry soils, there will be lower N mineralisation and less plant available nitrogen, reducing plant uptake but increasing soil nitrogen available to crops once moisture increases.
When we then experience increased rainfall and a sudden increase in soil nitrogen, we are hit with a period of grass growth simular to a 'spring flush'.
What effects will buffer feeding have during periods of low grass growth
During the period of reduced growth and pasture shortage buffer feeding was a necessity.
Hay was a chosen favourite due to its availability of it after ideal hay-making weather. This will affect the quantity of vitamin E the cows are receiving, like all tocopherols they have a low stability to heat, light and pH.
These properties cause vitamin E content to be low in grass silage, maize and hay. The relationship between selenium and vitamin E could potentially increase the selenium requirements in grazing animals leaving the animals possibly deficient.
Understandably these issues may not be of great concern in some areas now due to increased grass growth. However, going into the winter vitamin E and selenium levels need to be considered.
Dry soil and its impact on potassium movement
Soil with low moisture decreases the movement of Potassium (K) to the plant roots. As the soil dries the clay minerals become dry and shrink, trapping K tightly between mineral layers, once it is trapped it is unavailable for plant roots to uptake. Once soil is moist again the K is released and available to the plant.
Also, any previously applied fertiliser or muck in the period of hot weather not broken down, will be taken up more rapidly due to it solubilising. This K is likely to be taken up more rapidly by the growing grass than magnesium (Mg), this will lead to high K intake and a lower Mg intake which could result in hypomagnesia. A 20-30L cow at grass would require 25-30g supplemental magnesium, this includes what’s in the diet as a whole.
The higher K intake will also affect the sodium to potassium ratio therefore, it is important to provide your milking cows with rock salt. The reduction in soil microbial activity will also reduce organic matter decomposition and the mineralisation of organic phosphorus (P) to inorganic P, due to phosphorus moving from higher concentrations in the soil to lower concentrations in the plant roots.
Phosphorus unavailability is otherwise known as ‘pica’, symptoms include licking stones and other objects, it is most common in the spring with rapid grass growth.
In conclusion
Therefore, minerals are key for the cow’s performance, health and fertility and a key component of all diets. Daily mineral supply needs to be considered and the sources of minerals such as forage, water, concentrates, boluses, lick blocks etc.
To get a better idea of what your current situation is with regards to mineral supply a Forage Mineral Analysis can be carried out and a custom mineral can than be formulated to your requirements. Contact your local Dairy Specialist to book an appointment.
