Editor's note: The following article was published by the William H. Miner Agricultural Research Institute and featured in their Miner Institute Farm Report.
Accounting for the contributions of various adipose stores and understanding the hierarchy of fat deposition is essential to properly estimating energy mobilization for lactating cows. As I discussed in last month’s Farm Report article “Are skinny cows really skinny?”, having an accurate measure of energy mobilization is key, and the use of ultrasound to determine back fat and kidney fat in addition to routine body condition scoring are necessary parts of transition cow management. The importance of energy balance is most evident in the transition cow, as maintaining positive energy balance aids in a healthy and productive transition into lactation. However, maintaining energy balance starts before cows even enter the parlor — in the dry period where energy intake should be moderate so that there isn’t excess energy intake which can lead to a plethora of metabolic disorders in fresh cows.
One such metabolic disease that’s tied to improper energy intake during the dry period is hepatic lipidosis, commonly known as fatty liver. Fatty liver is an accumulation of triacylglycerol in liver tissue that impairs proper liver function. Fatty liver also alters immune response negatively and increases vulnerability to a variety of diseases including metritis and mastitis. Fatty liver is often unseen in dairy cows because there aren’t external indications that fat is accumulating in the liver as the dry cow progresses through the fresh period. Detecting fatty liver would be a beneficial part to any fresh cow program, as it’s been reported to affect up to 50% of all dairy cows in the transition period, resulting in a cost of over $60 million for U.S. dairy farmers.
So how can we detect fatty liver if there are typically no outward signs of its development? Just as I discussed the use of ultrasound to fully assess and quantify body fat stores last month, ultrasound can be used to detect the amount of triacylglycerol in liver. Ultrasound can determine the percentage of fat in liver tissue that’s much less invasive than the traditional liver biopsy or post-mortem diagnosis. Imaging liver using ultrasound produces a “distinct texture pattern” as described by Amin et al. (2001) that’s attributed to small changes in the echostructure of liver caused by fat accumulation.
Ultrasounds of liver with high fat content often appear darker and slightly more blurry when compared to cows with healthy liver tissue. This is due to the increased vascular blurring and acoustic backscatter caused by accumulation of fat in liver. As the fat content of liver increases, the normally white/gray mass that is liver being ultrasounded begins to darken toward grey and progresses toward black when triacylglycerol content is above 20%. The progression from white/gray to black with increased triacylglycerol in liver allows for a gradient of fat accumulation in liver to be developed.
Through the use of ultrasound a large number of cows can be scanned within a short time period without any invasive methods to determine if fatty liver is present in one’s herd. This is especially important if dairy farms are feeding high energy diets during the dry period, or possibly one group dry rations.
Research has shown that nutrition during the far off portion of the dry period may impact transition cow health in a greater manner than nutrition during the close-up phase. Dietary addition of rumen-protected choline may aid in the reduction of fat in liver as it increases fat exportation from liver. Regardless of the dietary strategy utilized to reduce fat accumulation in liver of transition dairy cows, minimizing triacylglycerol accumulation in liver is essential to maintain proper liver function. Allowing for proper liver function during the transition to lactation impacts animal health bolstering lactational performance and increasing animal well-being.