By Glenda Eden - AgriNews Staff Writer

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KEMPTVILLE— Researcher Dr, Gaëtan Tremblay offered farmers at Eastern Ontario Dairy Days in Kemptville, a farm-grown forage alternative to adding unpalatable anionic salts to rations during the transition period.

To prevent milk fever it isn’t enough to simply set aside old fields of hay to feed today’s high production cows in the weeks leading up to calving, farmers at the W.B. George Centre were told on Feb. 11.

Milk fever is characterized by paralysis shortly after freshening when demand for calcium quadruples at the start of lactation. This high and sudden demand can significantly drop calcium levels in cows not properly prepared before calving. According to Tremblay, a Quebec researcher with Agriculture and Agri-Food Canada, it is estimated that the economic loss in Quebec alone is about $9-million a year.

Adding anionic salts to the feed can be unpalatable and while full-blown milk fever can be treated with large doses of injected calcium, the damage is already done with decreased feed intake and milk production and a greater likelihood of other metabolic problems.

To prevent this metabolic disorder, which occurs within hours of calving in cows that have had two or more calves, a balanced cation-anion ration is necessary and achieved by lowering cations, mainly potassium (K) and sodium (Na), in the ration and/ or increasing the anion levels, cloride (Cl) and sulphur (S). This low dietary cation-anion difference (DCAD) in feed brings about a mild metabolic acidosis, which helps control, the level of calcium in the blood.

The first step to growing low DCAD forages is to grow them on low K soils and because DCAD varies from one forage to the next, selecting the best species is also important. Experiments carried out by Agri-Food Canada, said Tremblay, indicate that timothy is the preferred crop having half the DCAD of orchard grass hay.

DCAD levels for meadow brome, smooth brome and tall fescue fall midway between the orchard grass and timothy values. Researchers also found the average DCAD for five common legumes was 2.5 times higher than the average grasses in the study. These experiments go a long way in explaining why old fields produce good hay for transitional cows as the legumes have dwindled away and the hardy timothy has become the dominant grass.

The study also found no difference between grass cultivars or the application of nitrogen fertilizer on potassium-poor soil, however, application of inorganic fertilizer is best as potassium-rich liquid and solid manure will affect DCAD levels.

The science bears out the old hay field practice — timothy is better than other forages for feeding dairy cows in the transitional period. To economically grow low DCAD timothy, a spring application of chloride fertilizer at a rate of 100 kg per hectare on a field with low potassium soil is suggested. To grow low-DCAD second-cut timothy Tremblay recommended 65 kg after the first cut. The second cut will have a slightly lower DCAD level but both are acceptable.

Growing low DCAD forages can replace the use of anionic salts to maintain normal calcium blood levels with negatively affecting the cows feed intake.

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