Fresh cow milk fat to protein ratio (fat:protein) can be used to identify cows experiencing ketosis
Subclinical ketosis affects 26 to 55% of dairy cows and is conservatively estimated to cost dairy producers $78 per case. Ketosis is also correlated with increased risk for other transition cow disorders that decrease dairy farm profitability. Various studies have evaluated the effects of serum concentration of beta-hydroxy butyrate (BHBA) > 1400 µmol/L and found that there is an increased risk for displaced abomasum, metritis, severity of mastitis, and increased days to conception. Milk production is also affected by ketosis and results in a milk yield decrease of 3.0 pounds per cow per day in early lactation and annual milk yield reduction of 866 pounds for mature cows.
When cows lose body weight and body condition score rapidly after calving they are at a greater risk for ketosis and fatty liver. Blood non-sterified fatty acids (NEFA) 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 Think of NEFA as dollars that are withdrawn from a savings account and now can be spent on the things you want to accomplish.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, which affect milk production and immune function. The majority of NEFA in the blood is metabolized in the liver to provide energy and 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.
By identifying cows at risk for ketosis in the first day of lactation, producers can develop a cow watch list or implement feeding or therapeutic treatment practices preventing elevated ketones from occurring. Producers can then focus labor and treatment on cows resulting in the greatest return on ketosis prevention investment, increasing early lactation performance, and increasing cow welfare.
Proactive ketosis preventive treatment will reduce the incidence and severity of lipid related metabolic disorders and increase energy intake, with an impact of greater milk production. Current methods that measure elevated ketones (BHBA blood, urine, or milk test) are temporally reflective in that the cow is already experiencing the effects of subclinical ketosis.
Early lactation data from three studies including 176 cows that were combined to evaluate the efficacy of utilizing fat to true protein ratio (FPR) as a determinant of success of transition cow management. To evaluate FPR cut point for risk of lipid related disorders, cows were divided into two groups: less than (<) or greater than (>) 1.4 FPR during the first month postpartum. The objective of this retrospective analysis was to determine if first DHIA test FPR can be utilized to better understand transition cow success. Cows with a FPR > 1.4 had greater serum BHBA and NEFA on days 1, 7 and 14 after calving, indicating that cows with > 1.4 FPR had subclinical ketosis. They also had greater liver fat percent on days 7 and 14, and lost more body weight (BW) through the first four weeks of lactation. Yield of 305d milk tended to be greater for cows > 1.4 FPR. Utilizing FPR > 1.4 as a minimum cut point is an adequate herd level diagnostic tool for determining herd transition cow success as mean BHBA was > 1.2 mmol/L, which is the lower value for determining subclinical ketosis. FPR can also aid in the herd detection and management of negative effects such as elevated serum BHBA, NEFA and liver triglycerides as indicated by FPR > 1.4 with these cows having potential to increase ME 305d milk yield.
Success in the transition period is a good indicator of whole farm management. Over the past five years, our research group at the University of Minnesota has been studying what we call "Adaptive Nutrition", which is a nutrition and management strategy aimed at minimizing the impact of change in metabolism associated with changes in the dairy cattle life-cycle. Specifically we are looking for feeding and management strategies that achieve a high level of cow milk production 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.
Table 1. Effects of fat to true protein ratio on early lactation lipid metabolism and milk production
|FPR < 1.4||FPR > 1.4||SEM||P-value|
|BHBA||d 1, mmol/L||0.96||1.22||0.08||0.01|
|d 7, mmol/L||0.86||1.34||0.12||< 0.01|
|d 14, mmol/L||0.77||1.25||0.13||< 0.01|
|NEFA||d 1, µEq/L||442.14||603.57||45.24||< 0.01|
|d 7, µEq/L||575.29||857.44||51.23||< 0.001|
|d 14, µEq/L||513.31||715.50||42.96||< 0.001|
|Liver fat d 7, %||3.80||9.53||0.99||< 0.001|
|Liver fat d 14, %||4.11||7.70||0.73||< 0.001|
|BW change, lb||-74.0||-131.4||13.0||< 0.001|
|ME 305d milk, lb||23,347||25,443||922||0.08|