Research Update: Mineral Metabolism and Nutrition-Reproduction
Published: October 28, 2008
Source : Cornell University PRO DAIRY
Jose Eduardo Santos, who recently joined the faculty of the Department of Animal Sciences at the University of Florida, discussed interactions of nutrition and reproduction. While at the University of California-Davis, Santos conducted research on commercial California dairies related to the interactions. Here are summaries of Goff’s and Santos’ presentations.
Mineral-related disorders
The low point in blood calcium concentrations occurs between 12 and 24 hours post-calving, Goff said. Although clinical milk fever is rare in first-calf heifers, nearly 25% of them will have blood concentrations below normal, or less than 8 mg/dL. The percent is higher for older cows, with approximately 50% of them having low blood calcium after calving.
With effective implementation of milk fever prevention strategies, you can cut those percentages in half and reduce clinical milk fever to 1% or less. Several major factors impair cows’ ability to
maintain normal blood calcium concentrations after calving, Goff said. They include:
* Metabolic alkalosis. This is where blood acidbase balance is shifted toward a slightly higher pH. It occurs primarily when the balance of cations, chiefly potassium and sodium, is greater than anions, principally chloride and sulfate, in the ration fed before calving.
By decreasing cations and adding anions, you help cows to mobilize calcium from bone and increase efficient absorption of calcium from the intestine.
* Blood magnesium status after calving. Low blood magnesium – less than 1.8 mg/dL – affects calcium metabolism by interfering with hormonal controls that help to mobilize calcium from bone and absorb it from the intestine.
Blood magnesium status is controlled primarily through absorption of magnesium from the rumen. It’s typically increased by feeding more magnesium in rations.
High levels of ration potassium also can interfere with magnesium absorption. Very low blood magnesium – less than 1.15 mg/dL – also can result in tetany or other signs of clinical hypomagnesemia. This is treatable with oral magnesium.
See Table 1 for Goff’s general guidelines for mineral content of a precalving ration.
For chloride, the concentration required to achieve metabolic acidosis is approximately the ration potassium content minus 0.5%. So if ration potassium in the precalving ration is 1.3%, then 0.8% chloride would be needed to acidify the cow.
Different chloride sources vary in their palatability and their effects on dry matter intake, Goff said. Ammonium chloride and ammonium sulfate can be unpalatable.
Anionic sources based upon hydrochloric acid will be more palatable.
If you use anionic sources in diets, Goff recommends monitoring them using urine pH 48 hours or more after a ration change. Closeup Holstein cows fed anionic diets should have an average pH between 6.2 and 6.8. For Jerseys, urine pH between 5.8 and 6.3 can effectively control hypocalcemia.
Oral calcium treatments at calving can prevent hypocalcemia, Goff said. Between 50 and 125 grams of calcium per dose given at calving and again 24 hours later produce the best results.
Calcium chloride is effective but can be caustic. Goff prefers calcium propionate, which is less caustic and also provides propionate which cows use to make glucose. Benefits of oral calcium treatments are minimal when dietary strategies to prevent hypocalcemia are well-implemented, Goff said.
Nutrition and repro
High quality nutritional management before and after calving, combined with cow comfort, forage quality and feed availability, maximizes nutrient intake and minimizes loss of body condition score (BCS), said Jose Eduardo Santos.
There’s strong evidence to support the importance of nutrition to reproductive performance: Thinner cows during early lactation are less likely to cycle. And the risk increases dramatically as BCS drops below 2.75. Cows that lose more than one BCS unit in early lactation have significantly lower conception rates and greater pregnancy loss than cows that lose less BCS.
Substantial research exists to show the need to minimize disturbances in dry matter intake in cows during late pregnancy and early lactation, Santos said. Three recent studies show that cows that developed metritis or subclinical endometritis had decreased feed intake and feeding behavior beginning up to two weeks before
calving.
Research confirms that cows with subclinical endometritis, based upon uterine cytology from uterine flushes,
showed dramatically lower conception rate at first AI service. Subclinical endometritis is related to both retained placenta and metritis.
Energy-related disorders, such as subclinical ketosis, are another set of conditions with negative impacts on reproduction. These disorders also increase days open, Santos said.
There are several ways fat supplementation can influence reproduction, he said. Although it potentially increases a ration’s energy density, the effects of fat supplementation are more closely related to the influence of specific fatty acids on reproduction.
Unsaturated fatty acids found in some plant and marine sources can potentially increase the supply of these fatty acids for absorption. One study showed that supplementation of linoleic and trans-monounsaturated fatty acids improved embryo quality, Santos said.
Reproductive success relies on a team effort among a dairy’s management, staff, veterinarian and nutritionist combined with healthy cows, sound nutrition and health programs, and effective reproductive strategies.
Table 1. Guidelines for mineral content of precalving ration
|
Mineral |
Content |
|
Calcium |
0.85 to 1.0 |
|
Magnesium |
0.35 to 0.4 |
|
Phosphorus |
~ 0.4 * |
|
Sulfur |
> 0.22 but < 0.4% of the diet |
|
Potassium |
As low as possible to 1.0% |
* More than 80 grams of phosphorus per day can cause milk fever.
Author: Tom Overton
PRO-DAIRY publication - Cornell University
■ Tom Overton is associate professor of animal science and associate director of the PRO-DAIRY program at Cornell.
■ Jesse Goff is director of research and development for West Central Cooperative in Ralston, Iowa.
■ Jose Santos is associate professor in the Department of Animal Sciences at the University of Florida.
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