Post Drought management. The first significant rains after a long dry period trigger rapid pasture growth.
Post Drought Management.
The first significant rains after a long dry period trigger rapid pasture growth. The catalyst is nitrate (NO3) that has accumulated as a result of soil biological activity and dormant plants. The forage grown as a result of luxury feeding on nitrate can contain grossly elevated levels of crude protein. Forage, especially perennial rye grass, with elevated crude protein levels presents a challenge for the animals.
Below is a comparison of the mineral composition of perennial ryegrass versus plantain versus optimum herbage mineral levels (Brunetti).
Crude protein is also known as non protein nitrogen (NPN) because it contains very little amino acids. Because of the absence of amino acids NPN is not recognised as an energy source by the animal’s gut so it is dealt with by the animals waste disposal system (blood, liver and kidneys) and is eventually excreted in urine. True protein held in well grown forage contains a full array of amino acids and, in this form, is recognized as an energy source by an animal’s gut.
To calculate crude proteins multiply the forage nitrogen percentage by 6.25. The ryegrass analysis above contains 5.6 x 6.25 = 35% crude protein. Plant physiology limits true protein content to about 20% so the ryegrass above is offering 15% of its protein as crude protein (potassium nitrate) to its consumer. The animal’s metabolism deals with crude protein the same way the human metabolism deals with alcohol. Both are not recognized as energy and are consigned to the waste disposal system. The excess is carried in the blood stream until the liver can “catch up”. In both cases the consumer suffers from a hangover caused by a temporary drop in blood oxygen levels (anoxia). The collateral damage to the grazing animals is significant. Cows suffer conception failure or embryo loss, mastitis, elevated cell counts and lameness. Anaerobic blood creates an environment for internal parasites to reproduce effectively in young cattle and sheep.
The antidote for crude protein is calcium and magnesium. The plantain analysis above reports 22.5% crude protein. The ryegrass reports 600% more crude protein than the plantain. The plantain contains approximately 300% more calcium as well as significantly more trace minerals. When grazing animals have access to a diverse grass, clover and herb sward when crude protein levels spike in the ryegrass they will self medicate and balance themselves with the herbs and clover. They can be observed picking the plantain and clover out of the sward before they start eating the ryegrass because the ryegrass is basically toxic and will only be eaten when there are no other options. It is common to see animals that have been put onto a brand new regrass paddock eating the edges of the paddock and the headlands and push their heads through the fences to eat the feed outside the fence before they will eat the new grass.
Consultants and fertiliser company technical staff are promoting the application of urea as soon as the drought breaking rains arrive. Citing results of trials done in Bay of Plenty, Waikato and Manawatu they claim better “dry matter” production resulted from urea applied at the first rain as opposed to waiting for follow up rain. If the pasture is ryegrass dominant the strategy will be effective as long as the dry matter is intended only for the manufacture of fireworks! Gun powder is made from potassium nitrate, charcoal and sulphur. The excess potassium nitrate already in the grass will have already rendered it unpalatable without applying more nitrates to a nitrate saturated soil environment!