THE health of dairy cows after giving birth plays a big factor in the quantity and quality of the milk the cows produce. Now, researchers at the University of Missouri have found that subclinical hypocalcemia is related to higher levels of fat in the liver.
John Middleton, a professor in the University of Missouri College of Veterinary Medicine, said these higher levels of fat are often precursors to future health problems in cows.
"We found that about 50% of dairy cows suffered subclinical hypocalcemia and subsequent higher levels of fat in the liver after giving birth to their calves," Middleton said. "These higher levels of fat in the liver are often tied to health problems in dairy cows, including increased risk for uterus and mammary infections as well as ketosis, which is a condition that results in the cows expending more energy than they are taking in through their diet. All of these conditions can decrease the amount of milk these dairy cows will produce."
Middleton, along with Jim Spain, university vice provost for undergraduate studies and professor of dairy nutrition in the College of Agriculture, Food & Natural Resources, studied 100 dairy cows over two years to determine how subclinical hypocalcemia affected the health of the cows after they gave birth. Previous research done at the university has found that these issues also have a negative impact on cow fertility and reproduction.
While Middleton and Spain did not find any direct links to health problems in cows, they said correlations with higher levels of fat in the liver call for further research into the health implications of low blood calcium levels.
Dairy cows begin producing milk after giving birth and continue for 11-12 months until they are "dried off" by a dairy farmer about 45-60 days before their next calving.
To maximize the health of the cows and the amount of milk they produce, Middleton recommends paying close attention to dietary management in the late-dry/early-lactating period as well as providing supplemental sources of calcium during early lactation for cows that are at risk for subclinical hypocalcemia.
"Because our study suggests some potential risks for health issues in dairy cows with subclinical hypocalcemia, it is important for dairy farmers to monitor these levels in their cows," Middleton said. "For herds experiencing a high incidence of subclinical hypocalcemia around the time of calving, adding anionic salts to their diets or providing calcium solutions orally or by injection at the time of calving could be beneficial to their overall health and productivity."
This study was published in the Journal of Dairy Science.
Nutritional and management practices can have a major effect on a dairy cow's immune system during the transition period, and minimizing stress in close-up and fresh cows is important in supporting their health, milk production and reproductive efficiency, according to Dr. Robert Corbett of Dairy Health Consultation in Spring City, Utah.
During a preconference symposium sponsored by Prince Agri Products at the 2013 Penn State Dairy Cattle Nutrition Workshop, Corbett noted that dairy cows experience a suppressed immune system at parturition that is caused by the release of the stress hormone cortisol, which makes them more susceptible to mastitis and a host of other health disorders. Elevated blood cortisol, he explained, causes white blood cells — neutrophils — to lose their ability to fight infections.
"Any effort that can be made to reduce stress on the dairy cows will result in an improvement in their immune function, which is their first line of defense against the common infectious diseases that occur around the time of calving," he said.
Corbett outlined cow comfort and other management practices to reduce stress and enhance transition cow health, including avoiding overcrowding and providing environmental cleanliness and milking hygiene. He encouraged producers to maximize dry matter intake, ensure adequate energy and protein in transition cow rations and provide nutritional supplements to help improve energy and support the immune system.
"Immune-suppressed livestock are more susceptible to infections and may experience challenges to other productive functions," he said.
Role of blood calcium. To minimize the drop in blood calcium levels at parturition, Corbett recommended feeding transition cows a negative dietary cation-anion difference (DCAD) diet with the goal of reducing potassium and sodium levels and increasing chloride and sulfur levels.
Noting that clinical and subclinical hypocalcemia are major underlying causes of problems in transition and early-lactating cows, he said a high percentage of metabolic disease problems as well as impaired immune function are directly correlated to low calcium levels.
Corbett explained that subclinical hypocalcemia — a drop in blood calcium, but not low enough to be classified as milk fever — can affect 25% of first-calf heifers and 50% or more of second-lactation and older cows if they are not on a negative DCAD ration.
"Hypocalcemia is like an iceberg: most of the problem may be below the surface and hard to detect," he said. "Laboratory analysis of blood samples from fresh cows within 24 hours of calving is the only way to diagnose subclinical hypocalcemia."
He said calcium is often described as the second messenger of the immune system and is important in all muscle contractions, including the gastrointestinal tract.
"Dairy producers must minimize the drop in blood calcium at parturition to maximize dry matter intake and prevent immunosuppression," he emphasized.
An ongoing project conducted on 427 dairies throughout the U.S. during the past six years has demonstrated the importance of a well-functioning immune system to support dairy cattle health and milk production.
The project, known as the Immunity Challenge, conducted by Prince Agri Products, enables dairy owners, veterinarians and feed consultant professionals to evaluate the benefits of including an immune-supporting nutritional supplement in a best practices nutritional program for dry and lactating cows.
"Healthy cows, in general, produce more milk, rebreed sooner and have longer, more productive life spans," said Dr. Jim Chapman, a Prince Agri Products dairy technical manager who leads the study. "The modern-day dairy cow, because of the physical and metabolic demands associated with high milk production, may be predisposed to opportunistic diseases or infections, resulting in reduced time spent in profitable milk production."
The study utilizes Prince Agri Product's OmniGen-AF nutritional supplement. The program involves adding the supplement to cow diets for 90 days and then measuring changes in the herds' health and milk production compared to the 90-day period prior to adding the nutritional supplement.
The project has included herd sizes ranging from 38 to 6,700 milking cows, with a total of 273,707 cows in the project.
Results from 2007 through 2012 included:
* Reduced disease and other health events. There were 13.6% fewer mastitis cases per month, a 20.0% reduction in retained fetal membrane cases as a percentage of fresh cows, a 22.6% reduction in metritis cases as a percentage of fresh cows, a 16.7% reduction in cows delivered to the hospital pen and a 23.2% reduction in total herd death loss.
* Lower somatic cell count (SCC). Bulk tank SCC averages were tracked through the 90-day feeding period. Of the herds summarized in the project, 72.6% reported a drop in bulk tank SCC of just more than 50,000. Sixty-three percent of the herds were at an SCC of 300,000 or lower prior to starting the program.
* Increased milk production. The research also showed a positive effect from the supplement on pounds of milk produced, although that was not a focus of the study.
"Proper management and good nutrition can help support a cow's natural immune system, which, in turn, can reduce the occurrence of disease, lower treatment costs and improve milk quality and milk production," Chapman said.
Red clover silage
Fat is an important ingredient that has a material impact on the nutritional value, texture, taste, shelf-life and producer price of milk. Since milk products are a significant source of saturated fatty acids in the Western diet, researchers in Finland examined how dairy cattle should be fed so that their milk contains more unsaturated fatty acids.
Only scant research data are available on the effects to the lipid metabolism of ruminants from the forage conventionally fed to dairy cows.
In her doctoral thesis, Anni Halmemies-Beauchet-Filleau, who has worked as a researcher at MTT Agrifood Research Finland and at the University of Helsinki, studied the role of forage species and conservation method in ruminal lipid metabolism and milk fatty acid composition.
The practical aim was to develop a feeding strategy that decreases the share of saturated fatty acids and increases the share of unsaturated fatty acids, particularly oleic acid and alpha-linolenic acid (omega-3), in milk fat composition.
Approximately half of milk fat is generated in the mammary glands of cows, while the other half comes from the fats in forage, an announcement said.
Most of the unsaturated fatty acids in forage go through biohydrogenation, i.e., they become saturated in the rumen. In addition, as a result of feed fermentation, fat precursors are formed in the rumen, which develop into saturated fatty acids in the mammary glands.
"Feeding can be used to affect the lipid metabolism of the rumen and the mammary glands and, thereby, the fat composition of milk," Halmemies-Beauchet-Filleau explained.
The effect of the forage conservation method was examined in two tests using fresh grass, hay or silage prepared with or without an acid-based additive.
The most advantageous effect on lipid metabolism is produced by forage from pasture or fresh-cut grass. Cows fed fresh grass use more fatty acids originating in adipose tissue to form milk fat than other cows do, the researcher said.
"Fresh grass decreases the share of saturated palmitic acid and increases the share of unsaturated oleic acid in milk fat compared to hay feed," Halmemies-Beauchet-Filleau said.
As for hay feeding, this accentuates the share of saturated fatty acids originating in the mammary glands. The differences in milk fat composition between hay and silage feedings were minor, she noted.
Milk fatty acid composition was also investigated by replacing grass silage with red clover silage and using a compatible vegetable oil supplement (rapeseed, sunflower and camelina). The changes in ruminal lipid metabolism are based on the differences between plant species in terms of digestion kinetics and microbial flora in the rumen.
"Replacing grass silage with red clover accomplished a distinct decrease in the saturation of fatty acids in the rumen and increased the concentration of alpha-linolenic acid in milk fat," Halmemies-Beauchet-Filleau noted.