Can you guess your cow's NEFAs?
Success in the transition period is a good indicator of whole farm management. Over the past five years my research group at the University of Minnesota has been studying what we call "Adaptive Nutrition". Additive nutrition is a nutrition and management strategy that aims to minimize the impact of change in metabolism associated with changes in the dairy cattle life-cycle. This concept can be applied to any animal management system but we focus mostly on application of these principles towards transition dairy cows and nursery calves. Specifically we are looking for feeding and management strategies that achieve a high level of cow milk production or calf growth with low risk of metabolic stress that can increase the risk of health disorders. For fresh cows, successful feeding strategies maintain energy intake, avoid metabolic stress, reduce negative health event risk and maintain liver health. Key components include: maintaining a high level of feed intake pre-calving without over-feeding energy and gaining body condition score, and maintaining feed intake after calving to minimize body condition loss.
Figure 1. Blood ketones (BHBA) concentration of cows grouped by serum non-esterified fatty acids (NEFA) concentration seven days after calving.
When cows lose body weight and body condition score rapidly after calving they are at greater risk for ketosis and fatty liver. Blood NEFA (non-esterified fatty acids) represent body fat mobilized from the cow's back, thighs, ribs, and abdomen. Think of NEFA as dollars that are withdrawn from a savings account that now can be spent on the things you want to accomplish. Blood NEFA are an important source of energy for the cow and may have some additional roles in altering metabolism that affect milk yield and immune function. The majority of NEFA in the blood is metabolized in the liver to provide energy, ketones, or is stored in the liver as fat. We know that high producing cows have higher or stronger hormonal signals that allow them to be elite cows. Some of those hormonal signals regulate the rate and extent of body fat mobilization. Although NEFA is a good thing, excessive NEFA can result in both ketosis and fatty liver.
How much NEFA is too much? We recently took a look back over the past four years of studies at the University of Minnesota St. Paul dairy barn and tried to answer this question. We arranged the cows into four groups based on their NEFA level; low, medium, high and very high (Figure 1), and then took a look at the ketones or beta-hydroxy butyrate (BHBA) from these groups of cows. Not surprising, the low NEFA cows also had low ketones. The medium NEFA cows had higher ketones, but were below the threshold of subclinical ketosis. The high cows had high enough ketones to be considered subclinically ketotic (> 1.1 mg/dL) but by 14 days after calving their blood ketones had dropped below the subclinical ketosis risk. The very high NEFA group had near clinical ketosis ketones that remained elevated on both 7 and 14 days after calving. The high and very high groups are clearly the cows that will give you the biggest return on your investment if you can identify those cows and effectively treat them for ketosis. The other take home message is that the medium NEFA group is the safest group as they had a very low risk for ketosis but also produced a similar amount of milk (Figure 2) compared with the high and very high NEFA groups.
Figure 2. Total 305-day lactation milk yield (pounds of milk/305 days) for cows grouped based on their serum non-esterified fatty acids (NEFA) concentration seven days after calving.
Our future studies will aim to develop practical on-farm methods to predict cows at risk for ketosis and to develop feeding and management strategies to consistently keep cows in the medium NEFA group. For now, we recommend targeting a body condition score between 3.0 to 3.5 at dry-off, feeding a good quality low energy diet during the dry period, maintaining feed intake after calving with good feed bunk management and comfortable environments, and quickly addressing low blood calcium issues.