By Alycia M. Burch and Ursula Abou-Rjeileh
Energy and nutrient demands of the dairy cow are heightened during the fresh period and remain high throughout lactation, depending on milk production needs. Feeding fat supplements can help meet this energy demand, and recent research has shown that specific fatty acids (FA) can help better meet these needs. A fatty acid of particular interest is oleic acid (OA), which may help to slow loss of body fat after calving and can also increase milk production, without affecting dry matter intake. Additionally, oleic acid may increase yield of milk and milk components in high producing, post-peak cows.
Fat in Dairy Rations
In most Federal Milk Market Orders, fat and protein yield are the major contributors to the price that dairy producers receive for milk. Between the two, milk fat is easier to manipulate - both positively and negatively - through nutrition. During the transition period, dietary strategies must harmonize yield of milk components with maintenance of healthy body condition. Additionally, energy demands of the dairy cow are different depending on her stage of lactation and level of milk production. Supplemental fat is often added to dairy cow rations to increase the energy density of the diet and to improve the yield of milk and milk components.
Supplemental fat can come in many forms, such as oilseeds, tallow, oils, and fatty acid supplements (prills and calcium salts). It is important to note that not all high-fat feeds are the same, as the fatty acid (FA) profile of the ingredients differ. We should not think of these feeds as just “fat” but should rather focus on the specific FA supplied by an ingredient.
Recently, research has progressed from feeding traditional animal and plant fats to feeding individual FA and blends of FA, as these FA have been found to affect metabolic and production parameters in dairy cattle differently. The most abundant FA found in commercial fat supplements are palmitic (PA), stearic (SA), and oleic (OA) acids, which are also the main three FA found in milk fat. Our research team has recently focused on these three FA and have examined different FA combinations to better understand specific ratios that can be tailored to stage of lactation and production level.
The Transition Cow
The transition period is a critical time, due to the cow experiencing sudden changes in nutrient demands and metabolic and immune functions. At the onset of milk production, the cow releases stored FA from body reserves to satisfy her energy demands. These FA are used as an energy source for calving, colostrum synthesis, and milk production. The FA are mobilized from adipose tissue, which is a specialized connective tissue that functions as the primary storage depot in mammals.
During periods of positive energy balance, the adipose tissue stores energy in the form of fat in a process known as lipogenesis. But during periods of negative energy balance (NEB), such as the fresh period in dairy cows, the adipose tissue breaks down fat for energy in a mechanism called lipolysis. As a result of NEB during the transition period, the rate of lipolysis exceeds that of lipogenesis. In normal circumstances, as lactation progresses, the rate of lipolysis slows and lipogenesis begins to restock the fat stores in the adipose tissue. This is regulated by changes in concentrations of hormones such as insulin.
Under normal circumstances, adipose tissue in fresh cows becomes resistant to insulin’s effects, which allows for the redirection of energy from the tissue to the mammary gland, supporting milk production. When this insulin resistance is moderate, it can ensure a healthy and productive lactation. However, in some situations, prolonged and excessive insulin resistance in adipose tissue can cause extreme lipolysis, which further intensifies NEB of the cow. Consequently, when NEB lasts for long periods of time, it puts the cow at a higher risk of developing diseases, reproductive problems, and performing poorly during her lactation.
Feeding Fatty Acids to Fresh Cows
Previously, dairy nutritionists generally advised against feeding fresh cows supplemental FA because of the FA from lipolysis already circulating in blood at that time, and the anticipated depression in feed intake, which could offset any advantage of increasing the energy density of the diet with fat. The past research with negative effects included FA at ~3-5% of dietary dry matter and used varying fat ingredients with differing FA profiles. Considering recent findings on effects of individual FA on mid-lactation cows, we began to question whether targeted FA supplementation to early lactation cows could be successful.
This led to a transition study where an 80% PA supplement was fed to fresh cows at 1.5% of the diet (DM basis) from 1-24 days in milk. Compared with a diet without FA supplementation, PA did not affect feed intake but increased energy-corrected milk by 10.4 lb/day. On the other hand, PA also decreased body weight and increased measures of lipolysis in the fresh period. These observations indicated that feeding PA promotes energy partitioning toward the mammary gland while increasing fat release from adipose tissue.
Results from two other experiments in post-peak cows feeding blends of PA and OA provided more insight into impacts of specific FA on energy partitioning. These post-peak cows showed increased body weight gain when fed the FA blends, suggesting a shift in nutrient partitioning toward adipose tissue with supplemental OA. These findings pointed to a potential use of PA and OA blends, designed to balance milk yield and maintenance of body weight, in fresh cows.
The follow up study for feeding OA to fresh cows, Study 1, was then conducted with three supplemental blends with varying ratios of PA and OA (80:10, 70:20, and 60:30) fed at 1.5% of diet DM for the first 3 weeks of lactation. When compared with a diet without supplemental fat, all three FA blends increased yields of milk and energy-corrected milk, and did not affect feed intake. When OA was increased in the supplement (from 10 to 30%), there was a reduction in body weight loss and plasma non-esterified fatty acids (NEFA) as well as an increase in plasma insulin. Plasma NEFA is a marker of lipolysis from the adipose tissue; although NEFA serves as an energy source in early lactation, high concentrations of plasma NEFA are associated with poor lactation performance. Hence, OA served to limit fat breakdown and enhance lipogenesis within the adipose tissue.
Given how well the fresh cows responded to the 60:30 (PA:OA) blend, we focused on that particular ratio in the next fresh cow study, Study 2. Similar to the previous results, we found that feed intake was not affected and yields of milk fat and energy-corrected milk were increased by the blend compared with a diet without fat supplementation, but we did not see a body weight difference between treatments.
Oleic Acid Increases Digestibility of Fatty Acids
We have routinely seen that OA increases FA digestibility in post-peak cows, and an increase in FA digestibility means that more FA are available to the cow for use for metabolic processes, such as milk synthesis in the mammary gland. In Study 1, we observed that increasing the level of OA in the supplemental FA blends increased total tract FA digestibility in fresh cows, similar to what we have observed previously in post-peak cows. The improvement in digestibility likely contributes to the production increases with cows supplemented with OA. It is unclear how OA increases digestibility, but we are confident that an adequate amount of OA in the diet is needed for optimal FA digestibility.
Adipose (fat cells) derived from subcutaneous adipose tissue from dairy cows in Study 3. Left: Cells in regular maintenance media; Right: Cells supplemented with 85 parts per million (300 µM) OA. Lipids are stained with Bodipy (green dye).
How Does OA Control Energy Balance in the Cow?
Compiling all this data together, we can see that feeding the correct blend of FA is crucial, as the 60:30 blend of PA+OA allows for improvements in production while minimizing body weight loss. This 60:30 ratio shows that there is a good balance between these two key FA, but what still was left unanswered was the exact mechanisms by which OA regulates energy balance. To better understand the mechanisms of OA, another fresh cow study, Study 3, was conducted utilizing cannulated cows so that we could infuse OA directly into the abomasum of the cow and thus bypass the rumen. These infusions were done for the first 15 days of lactation. Cows infused with OA had a lower rate of lipolysis in early lactation, reflected in decreased plasma NEFA and ketone levels.
We also collected adipose tissue samples from these cows, once before calving and twice post-calving. These tissues showed that OA limits lipolysis by promoting lipogenesis. After stimulating the tissue in the lab, we saw that adipose tissue collected from cows infused with OA has a reduced lipolytic response and an improved insulin sensitivity. These results could explain the reduction in body weight loss we observe when supplementing cows with OA.
Understanding the pathway that OA activates within the adipose tissue will help us develop more refined nutritional strategies to better harness OA’s lipogenic capabilities. We have recently identified two genes via which OA exerts its benefits - peroxisome prliferator activated receptor alpha (PPARα) and perilipin 5 (PLIN5). PPARα appears to be a counterbalance to control the harmful effects of chronic lipolysis. Similarly, PLIN5 limits lipolysis by promoting the formation of new lipids. The direct effect of OA on adipose tissue capacity to store fat was also demonstrated in isolated adipose cells, showing greater lipogenic capacity in response to OA (Figure 3).
Conclusion
Feeding fat supplements that are 60% PA and 30% OA can positively impact the transition cow by regulating the balance between increasing milk production parameters and sustaining body weight in this critical period. This information is important for dairy producers and nutritionists when feeding fat supplements to fresh cows to help meet energy demands and increase yields of milk and milk components. We are still working to fully understand the mechanisms linking supplemental OA to improved milk production, increased FA digestibility, and altered energy partitioning.
Source : msu.edu