Timothy Rated Tops for Dry Cows
The right forage fed to your dry cows can help prevent a metabolic disorder often affecting early-lactation cows.
A large percentage of your milking herd could be suffering from a low-level form of milk fever. Although afflicted animals will show no signs of the disease, their health, reproductive performance and milk production will suffer. By feeding the right forage during the dry period, however, you could reduce the incidence of this malady, improve overall herd health and lower operating costs.
Clinical milk fever, or hypocalcemia, typically affects six per cent of the cows in a dairy herd. Less acute forms, known as subclinical hypocalcemia, can affect up to 66 per cent of cows with one or more lactations.
Milk fever generally occurs immediately before or after calving when a cow resumes production of milk, prompting a sudden increase in calcium demand. The cow can't absorb sufficient calcium from her diet or mobilize it from her bones quickly enough to offset that demand. This reduces calcium concentration in her bloodstream and hypocalcemia occurs.
It has been well documented that a ration too rich in cations, or positive ions, such as potassium (K+) and sodium (Na+) slightly increase the blood pH. This decreases the efficiency of calcium mobilization from the bones, making the cow more prone to hypocalcemia.
A ration rich in anions, or negative ions, such as chloride (CI-) and sulfur (S2-) causes the blood to become slightly alkaline. This favours more efficient calcium mobilization from the bones, reducing the risk of hypocalcemia.
Differences between the amounts of anions and cations in the ration is called dietary cation-anion difference (DCAD). A calculation can determine the DCAD value of a diet (to see an example, visit the OMAFRA dairy nutrition page at www.ontario.ca /livestock). The usual formula to calculate DCAD is (K+ + Na+) - (CI- + S2-), although other equations are sometimes used. The result is often expressed in milliequivalents per kilogram of dietary dry matter (mEq per kg).
A desirable ration to feed a cow three to four weeks before calving has a negative DCAD of -50 mEq per kg. Several methods have been investigated to lower DCAD value. For example, adding anionic salts to a dry-cow ration will decrease the DCAD value, but cows find these salts quite unpalatable. Researchers have observed reduced dry matter intake when a substantial amount of anionic salts is fed to bring the DCAD value below zero.
Feeding forages with low potassium content is another option. However, growing low-DCAD forages on Ontario dairy farms poses a challenge since most have relatively high potassium levels in their soil.
Soil potassium content affects the final composition of the forage grown. When high amounts of soil potassium-more than 250 kg per hectare-are available, nitrogen fertilizer application can increase the grass's potassium content. When soil potassium supplies are less than 100 kg per hectare, nitrogen fertilizer application can decrease the potassium content.
A group of researchers investigated the DCAD value of five grass species grown on our farms. Orchardgrass, meadow bromegrass, tall fescue, smooth bromegrass and timothy were harvested twice a year during two production years. Results clearly indicate timothy has a lower DCAD than the four other grass species grown in Eastern Canada, making it best suited for producing forages fed to dairy cows during the weeks preceding calving.
Further investigations were conducted on timothy to verify whether a fertilizing program aimed at reducing the DCAD value of the forage could be effective. On four different sites, with different soil types and soil potassium contents, two different sources of chloride (CaCI2 and NH4CI) were applied at four different application rates: zero, 80, 160 and 240 kg of chloride per hectare. They were applied in combination with two (N) nitrogen application rates: 70 and 140 kg of N per hectare.
Results of these experiments established that using either source of chloride can lower a timothy-based forage's DCAD value. The optimal annual rate of chloride fertilizer varied from 78 to 123 kg per hectare, depending on soil potassium and chloride content. The annual rate was split into two applications, 60 per cent in spring and 40 per cent after first harvest. The most effective, economical way to produce low-DCAD timothy forage is growing it on fields with the lowest potassium content. Fertilizer type is crucial to the recipe for growing forages best suited to dry cow diets.
Researchers measured several parameters in the dry cows, such as blood components, urine pH and dry matter intake. Urine pH quickly shows whether a cow is responding to a low-DCAD diet. In this study, urine pH decreased to 5.89 from 8.21 when low DCAD hay was fed instead of the control diet. While there were no differences in the urine pH of cows fed the low-DCAD hay diet and the HCI diet, they preferred hay. Their dry matter intake was greater, at 11.5 kg per day, than for the HCI diet at 9.8 kg per day.
This experiment confirmed feeding low-DCAD hay effectively decreases the ration DCAD. Choosing a lowDCAD grass species, such as timothy, and growing it on a soil with low K availability and chloride fertilization should contribute to reaching the target DCAD of the dry-cow ration. A low-DCAD ration prompts a metabolic response in dry dairy cows that may help reduce the incidence and the extent of milk fever, increasing milk production and lowering production costs.
How to produce best forage for dry cows:
Charbonneau, E. Chouinard, P. Y. Tremblay G. F., Allard, G. and Pellerin, D.2007. Hay to Reduce Dietary Cation-Anion Difference for Dry Dairy Cows. j. Dairy Sci. 91:1585-1596;
Pelletier, S., G. Belanger, G. F. Tremblay, P. Seguin, R. Drapeau, and G. Allard. 2007. Dietary cationanion difference of Timothy (Pleum pratense L.) as influenced by application of chloride and nitrogen fertilizer. Grass Forage Sci. 62:66-77;
Tremblay, G. F., H. Brassard, G. Be'langer, P. Se'guin, R. Drapeau, A. Bregard, R. Michaud, and G. Allard. 2006. Dietary cation anion difference of five cool-season grasses. Agron. j. 98:339-348.
This article first appeared in the Ruminations column of The Milk Producer Magazine, June, 2008.
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