Real Science Exchange-Dairy

This Real Science Exchange podcast episode was recorded during a webinar from Balchem’s Real Science Lecture Series. You can find it at balchem.com/realscience.

Dr. Baumgard begins with an overview of the structure and function of the gastrointestinal tract. More than 75% of an animal’s immune system resides in the gut. The focus of this webinar is how heat stress initiates leaky gut, how that leaky gut then influences the immune and hormonal systems, and ultimately, how that reduces productivity. (0:22)

Dr. Baumgard compares the metabolism of a cow 200 days in milk to a cow 10 days in milk. The 200-day cow is experiencing ad libitum intake and gaining weight. Her insulin levels would be high, and NEFAs would be low. On the other hand, the 10-day cow is experiencing suboptimal intake, and her insulin levels are the lowest they’ll ever be during the production cycle. Body tissue is mobilized, and NEFAs will increase. Research shows it takes 72 grams of glucose to make one kilogram of milk. Any disruption to the gluconeogenic pathway has the potential to decrease milk yield. (6:38)

Heat stress is estimated to cost the US dairy industry $1.7 billion each year. Regardless of climate change, heat stress will continue to be an issue because all economically important phenotypes in animal agriculture are heat-producing processes. Dr. Baumgard’s lab has been investigating the biology of heat stress to implement more effective mitigation strategies. (9:09)

How much of the reduction in feed intake during heat stress explains the reduction in milk yield? A pair-feeding experiment comparing thermoneutral to heat-stressed cows showed that about 50% of the reduction in milk yield during a heat wave is due to a reduction in feed intake. The thermoneutral cows lost weight in response to decreased intake, and their NEFAs increased. Heat-stressed cows did not have an increase in NEFA. Heat-stressed animals fail to mobilize adipose tissue despite their endocrine profile predicting that they should. However, insulin is high when we would expect it to be low, and that response to heat stress is highly conserved in all species. (10:43)

Heat-stressed cows produced about 400 grams less lactose per day than their pair-fed thermoneutral controls. This is nearly a pound! Is the liver producing 400 fewer grams of glucose each day? Or is some other extramammary tissue using more glucose per day? Dr. Baumgard’s work suggests that the immune system is where the 400 grams of glucose go in heat-stressed animals. During heat stress, vasodilation at the body surface occurs, with concomitant vasoconstriction in the gut. The gut epithelium is very sensitive to reduced oxygen delivery that would result from the vasoconstriction, and tight junction proteins do not function properly, resulting in a leaky gut. This results in an infiltration of antigens into the body, which causes an immune response.  (15:36)

Dr. Baumgard details how insulin fits into these immune responses via the Warburg effect. An activated immune cell prefers glucose and needs it in high quantities. The activated cell switches from the Kreb’s cycle to generate ATP to aerobic glycolysis. This requires high insulin. The immune system requires approximately one gram of glucose per kilogram of metabolic body weight per hour. (25:03)

By far, the biggest impact a dairy producer can make to alleviate heat stress is to modify the environment physically: shade, fans, soakers, misters, etc. Investing in cooling cows improves production efficiency and profitability, summer fertility, animal welfare and health, and sustainability. Other important heat abatement considerations include adequate water availability, reducing walking distance to the parlor and time in the holding pen, and improving ventilation. Dry cows should also be part of any heat abatement strategy, as the benefits of cooling dry cows extends far into lactation. Dr. Baumgard also discusses different dietary management strategies for heat stress situations. (32:43)

In summary, heat stress decreases almost every metric of productivity and costs everyone in the industry. Reduced feed intake is only part of the problem. Heat-induced leaky gut results in biological consequences incredibly similar to any other immune activation, such as mastitis or metritis. For dairy producers, heat stress abatement should by far be their biggest priority. Once those infrastructure improvements are in place, dietary interventions are another good strategy to minimize the negative consequences of heat stress. (47:43)

Dr. Baumgard takes questions from the webinar audience. (49:22)

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In times of limited forage, dairy producers may need to feed diets lower in forage than is typical but would like to maintain milk production. In this study, two diets similar in neutral detergent fiber (NDF), starch, and crude protein with different amounts of forage were fed to 32 mid-lactation Holstein cows in a crossover design. The control diet (CON) contained high forage (55.5% of diet dry matter) with no supplemental fatty acids or amino acids. The low-forage diet (LF) contained 36.6% forage along with supplemental fat and rumen-protected methionine and lysine. As forage was removed from the LF diet, it was replaced with byproducts and high-moisture corn was replaced with dry corn. (4:42)

Dr. Lock added fat and amino acid supplements to the LF diet to not lose milk production. The fat supplement was a palmitic-acid-rich prill. Dr. Lock does not think the response would have been the same if a different fat supplement had been used. The LF diet was higher in fat and palmitic acid, but most other fatty acids were fairly similar between the two diets. (16:25)

Milk yields were similar between the two diets. Cows on the LF diet consumed about 1 kg more dry matter each day than CON-fed cows. Cows fed the LF diet also had higher milk fat and milk protein yields and content which led to an approximately 2 kg increase in energy-corrected milk compared to cows fed the CON diet. Dr. Lock believes the fat and amino acid supplementation were a key part of achieving these results, and they would not have seen the same response if those supplements had not been added to the LF diet. The LF diet spared around 5.5-6 kg of forage per day, and cows gained body condition.  (22:03)

Dr. Weiss asks Dr. Lock to speculate if low-forage diets fed for longer periods would have negative health impacts. Dr. Lock feels that usually production would be negatively impacted by cow health issues, which was not the case here. However, if high-moisture corn had been used in the LF diet, he predicts they would have seen negative impacts. (27:18)

What about low-forage diets for early lactation cows? Dr. Lock suggests looking at diets in other parts of the world where forage is limited and see how dairy producers manage diets in those instances. He speculates that lower forage could be successfully implemented in early lactation cows after the fresh period. (31:09)

Dr. Weiss and Dr. Lock discuss the apparent improved digestibility of the LF diet given the increased production. While byproduct ingredients are often more fermentable in vitro, the results don’t always translate in vivo. Palmitic acid supplementation has been shown to improve fiber digestibility, so that may have happened in this experiment. (32:12)

On the protein side, we’ve moved away from talking about crude protein in the diet and toward amino acid concentrations. Dr. Lock would like to see the same trend in the industry for fat in the diet. A good leap was made recently from ether extract to total fatty acids, and he hopes to see individual fatty acids as the next step in that evolution. He recommends two questions be asked when considering a new fatty acid supplement. What is the fatty acid profile? What is the total fat content? The appropriate fatty acid profile is going to depend on the basal diet and what type of cow is being fed. Dr. Lock’s preference is a palmitic: oleic acid blend around 70:20 or 60:30 early in lactation, with a higher palmitic blend later in lactation. He expects the current work with different oilseeds to provide some good recommendations for feed ingredients to incorporate to increase dietary fat.  (35:53)

As genetics continue to improve and nutrient requirements of cows continue to increase, is it conceivable that someday we are going to purposefully decrease fiber in the diet? While that may be the case, Dr. Lock reminds listeners that about half of milk fat comes from acetate and butyrate produced in the rumen, so fiber is still going to be critical. While we may lower the forage in a diet, forage quality is going to remain very important. (39:45)

The panel wraps up with their take-home messages from this paper. Clay looks forward to more research with a factorial design to further evaluate low-forage diets. Dr. Weiss reminds listeners there’s no one recipe for diets to achieve high yields of milk components. Lastly, Dr. Lock is excited about the future of research in this area and refining diet formulation in the area of fat supplementation. (43:21)

You can find this episode’s journal club paper from JDS Communications here: https://www.sciencedirect.com/science/article/pii/S2666910223001084

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This Real Science Exchange podcast episode was recorded during a webinar from Balchem’s Real Science Lecture Series. You can find it at balchem.com/realscience.

Dr. Santos begins with a timeline of events that occur during the cow’s transition from the dry period to her exit from the fresh pen. He suggests that cows should be dried off at around 230 days of gestation, then moved to a closeup group at 250-255 days gestation which is around three to three-and-a-half weeks before calving. Dr. Santos recommends keeping multiparous cows separate from primiparous cows and feeding to minimize metabolic disorders in early lactation. After calving, cow health needs to be monitored for early detection and treatment of disease. In addition, diets that do not limit voluntary dry matter intake should be fed. During the early postpartum period, controlling excessive weight loss and lipid mobilization is the goal.  (00:27)

What is the association between time spent in the closeup pen and disease? Research shows that around three to four weeks in the prepartum group is associated with the lowest risk of morbidity, maximum milk yield and highest pregnancy rates. How does a change in body condition during the first 65 days in milk impact cyclicity? How does 90-day milk yield impact cyclicity? Cows that lose one or more units of condition are less likely to be cyclic at the end of the voluntary waiting period. There is a small statically positive association between milk yield and cyclicity. Dr. Santos’ first take-home message is to avoid excessive body condition loss after calving. Cows should lose no more than 0.5 body condition units from the week before calving to the first AI. This can be accomplished by minimizing over-conditioned cows at dry-off and reducing the risk of disease in early lactation.  (6:13)

What about feed efficiency? Dr. Santos describes experiments comparing the 25% most efficient to the 25% least efficient cows. All cows produced the same amount of energy-corrected milk, but the most efficient cows ate four kilograms less feed each day. The risk of morbidity and the culling rate was the same for both groups, as was reproductive performance. Dr. Santos suggests we should not be afraid of selecting for feed efficiency while still optimizing intake in early lactation.  (18:23)

Morbidity negatively impacts intake in early lactation. Around one-third of cows are affected by disease in the first three weeks of lactation and almost 80% of the first disease diagnoses occur during the first three weeks postpartum. The earlier in lactation disease occurs, the longer the legacy effects from that disease can impact cow health and performance. Dr. Santos describes an experiment in beef cattle evaluating how an inflammatory response impacts nutrient partitioning away from performance. Early lactation morbidity not only makes a cow not want to eat, it also may shift nutrients away from production toward survival, resulting in fewer nutrients available for milk production and reproduction. Dr. Santos describes a series of experiments evaluating the impact of early lactation disease diagnosis on reproductive performance. Dr. Santos’ second take-home message is to stimulate dry matter intake and minimize disease in the early lactation period. (22:21)

How can we formulate diets that will improve reproduction? First, we should formulate diets that reduce the risk of disease. Then we should incorporate nutrients that are known to improve reproduction in cows. Dr. Santos describes how supplementation with rumen-protected choline decreases triglyceride accumulation in the liver and improves milk yield. He also details the mechanisms of using acidogenic diets to reduce hypocalcemia. He recommends not using these diets for heifers and feeding them for around 21 days to cows rather than the entire dry period. Dr. Santos feels that forage quality has been neglected in the transition period and details how improved fiber digestibility during the transition period can have longer-term impacts. Lastly, he recommends feeding 1-1.5% supplemental fat in early lactation diets for improved reproduction and milk yield without negative impacts on body condition. In closing, Dr. Santos presents a summary of diet formulation recommendations for transition cows.  (34:13)

Dr. Santos leads an engaged question-and-answer session with the webinar audience. (51:11)

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In this episode, we honor and celebrate the remarkable career and contributions of Dr. Jim Drackley from the University of Illinois, a pioneer in dairy science and animal nutrition. Jim’s work has reshaped our understanding of dairy cow health, metabolism and nutrition. Dr. Cardoso, Dr. Overton, and co-host Dr. Jeff Elliott are former coworkers or graduate students of Dr. Drackley’s. (0:11)

Dr. Drackley begins by telling the audience about his background and how he became a dairy scientist. He talks about several of his mentors during his schooling. (9:20)

Speaking of mentors, Scott asks Dr. Elliot, Dr. Overton, and Dr. Cardoso to describe Dr. Drackley’s mentorship of them during teaching, graduate school and beyond. They praise Jim’s thoughtfulness and hands-off approach that taught them to think critically. (14:06)

When it comes to major contributions to the industry, Dr. Drackley names two that he is most proud of: expanding the knowledge of controlled energy dry cow programs using straw and corn silage to help control energy intake and his work in baby calf nutrition, specifically feeding more milk on-farm to calves. Dr. Overton adds that a visionary paper Dr. Drackley wrote in the late 1990s where he referred to the transition period as the final frontier as another important contribution. Dr. Cardoso also emphasizes Dr. Drackley’s excellent teaching skills as another achievement of note. (20:58)

Dr. Drackley says the teaching part of the job was the part that scared him the most when he started. Graduate school offers little formal teaching training and experience so one learns on the job. Jim describes his teaching style as organized, and he liked teaching in an outline fashion, working from the main topic down through the details. He worked hard to get to know the students, learn their names as soon as possible, and be approachable and empathetic. Later in his career, he used a flipped classroom approach for a lactation biology course and enjoyed it. (28:45)

The panel then reminisces about how much technology has changed from a teaching perspective as well as statistical analysis. Lecturing has moved from chalkboard to overhead projector to slide carousel to PowerPoint. Statistical analysis has moved from punch cards or sending data to a mainframe computer to performing real-time statistical analysis on your computer at your desk. (33:00)

Jeff, Phil, and Tom share stories and memories of their time with Jim. (37:30)

Scott asks Jim what challenges will need to be tackled in the future in the dairy industry. He lists environmental aspects (nitrogen, phosphorus, and greenhouse gases), increasing economic pressure on farms, and improving forage production and efficiency of nutrient use. Dr. Drackley’s advice for young researchers is to carve out a niche for yourself. (47:40)

Dr. Elliott, Dr. Overton, and Dr. Cardoso share some final thoughts paying tribute to Dr. Drackley and his accomplished career. (1:06:18)

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This Real Science Exchange podcast episode was recorded during a webinar from Balchem’s Real Science Lecture Series. You can find it at balchem.com/realscience.

How can we increase milk protein and capture that income opportunity? Dr. Van Amburgh describes the seasonal drop in milk protein observed in the summer months. Heat stress may play a role in altering insulin sensitivity and how the cow partitions nutrients. What can we do to avoid that seasonal decline in milk protein?  (0:01)

Simple things like cooling, fans, and sprinklers can reduce heat stress and increase cow comfort. Dr. Van Amburgh recommends promoting dry matter intake and lying time, with feed available 21-22 hours per day and more than 12 hours of lying time per day. (5:27)

Dr. Van Amburgh discusses basic formulation considerations for amino acid balancing including current feed chemical analyses that include NDF digestibility, characterizing the cows appropriately by using accurate body weights, understanding DMI and making sure actual milk lines up with ME and MP allowable milk, assessing body condition changes, and understanding the first limiting nutrient of milk production. Areas where mistakes are often made include using much lighter body weights than actual to formulate rations, not using actual DMI, and using feed library values instead of actual feed chemistry. (8:00)

Milk protein percentage and dietary energy are closely aligned. This is often attributed to ruminal fermentation and microbial yield. Sugars, starches, and digestible fiber sources drive microbial yield. While protein and energy metabolism are considered to be separate, that is an artificial divide and they should be considered together. Once adequate energy for protein synthesis is available, providing more dietary protein or amino acids can increase protein synthesis further. Dr. Van Amburgh provides some ranges of target fermentable non-structural carbohydrates, starch, sugar and soluble fiber appropriate for early peak and mid-lactation cows. He speaks about the benefits of adding sugars to the diet instead of trying to continue to increase starch. (11:15)

Dr. Van Amburgh details an experiment using more byproduct feeds in a lactation diet to successfully increase intake and subsequently, milk protein content. (24:04)

Milk protein increases with higher DCAD in diets, independent of protein level. Increasing DCAD can also lead to increased DMI, probably through better fiber digestion. The mechanism is not completely understood, but perhaps some rumen microbes have a higher requirement for potassium. In another study, feeding higher DCAD resulted in an 11% increase in milk protein yield and a 26% increase in milk fat yield. (32:39)

Feeding fatty acids may also improve milk protein via insulin signaling pathways. A 5.6% increase in milk protein was observed when the ratio of palmitic acid to oleic acid was around 1.5:1. (36:21)

Dr. Van Amburgh encourages the audience to pay close attention to digestibility of dietary ingredients and shares an analysis of ten different sources of feather meal that varied in digestibility from around 50% up to 75%. (40:10)

Dr. Van Amburgh details an experiment targeting optimum methionine and lysine levels for improved milk protein. In an example with 60 Mcals of ME in the diet, the targets were 71 grams of methionine and 193 grams of lysine. (42:00)

Questions from the webinar audience were addressed. They included information about the best type of sugars to add to diets, if protozoa are preferentially retained in the rumen, BMR vs conventional corn silage, amino acid supply when dietary crude protein is around 14-15%, using metabolizable energy instead of net energy, variability of animal protein blends, and methionine to lysine ratios. (48:23)

To end this podcast, Dr. Jose Santos steps in to invite everyone to the Florida Ruminant Nutrition Symposium in Gainesville held February 24-26.

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In this study, two basal diets were fed, one low-fat and one high-fat. The low-fat diet contained cottonseed meal and cottonseed hulls and the high-fat diet contained whole cottonseed. This balanced fiber and protein to try and make the difference between the basal diets and just the fatty acids. Basal diets were supplemented with two different fat supplements that had different ratios of palmitic and oleic acids. The applied question at hand was “Does fat need to be supplemented to a high-fat basal diet?” (5:32)

The low-fat diet contained 1.93% fatty acids and the high-fat diet contained 3.15% fatty acids. Fatty acid supplements were fed at 1.5% of dry matter and replaced soyhulls. The palmitic acid supplement contained 80% palmitic acid and 10% oleic acid. The palmitic + oleic acid supplement contained 60% palmitic acid and 30% oleic acid. Thirty-six cows were used in a split-plot Latin square design, with half the cows on each basal diet. Under each split-plot, cows were allocated to a 3x3 Latin square, evaluating a control treatment (no fat supplement), palmitic acid supplement, and palmitic + oleic acid supplement. (8:46)

Bill, Adam, and Clay discuss the increase in milk components the industry has experienced recently due to the powerful combination of genetics and nutrition. Hoard’s Dairyman reported that 2024 was the first year that the U.S. had averaged over 4% milk fat going back to 1924 when records began. (13:01)

Both fat supplements increased milk yield in low-fat and high-fat basal diets, but the magnitude of the increase was larger in the low-fat diet. The high palmitic acid diet increased milk yield more in cows fed the low-fat basal diet than the palmitic + oleic supplement did. High-fat basal diet cows had similar milk yield responses to both fatty acid supplements. The panel discusses the industry emphasis on milk components and if/when a threshold in performance might happen given the advancement of genomics and nutrition. (15:51)

Clay asks Adam to remind the listeners about the relationship between fatty acids and crude fat or ether extract. Adam recommends moving away from ether extract and focusing solely on fatty acid content. Bill, Adam, and Clay talk about the variability in the fatty acid content of various feedstuffs. (25:33)

Bill asks if the feed efficiency improvement with the fat supplementation was due to more of a gross energy or digestible/metabolizable energy effect. Adam suggests it may be a little of both. The diet is more energy-dense, but we also know now that some of those specific fatty acids have specific effects. Improvements in NDF digestibility are consistently observed with palmitic acid supplementation. Oleic acid improves fatty acid absorption and has an impact on adipose tissue metabolism and insulin sensitivity. Bill and Adam go on to talk more philosophically about the best way to measure feed efficiency in dairy cows. (29:02)

If Adam could do this experiment over again, he would have pushed the basal fat levels a bit more and had both lower-producing and higher-producing cows in the experiment. This leads to a discussion of how the results might have differed if distiller grains or soybeans were used instead of cottonseed in the experiment. Listeners should be careful not to extrapolate the results from this experiment to other fat sources. (33:55)

Adam emphasizes that we shouldn’t be afraid of feeding high-fat diets, either basal or supplemental fatty acids, especially to high-producing cows. We should be very mindful about where those fatty acids are coming from. We could provide the same nutrients by feeding either cottonseed or distillers grains, but how those ingredients feed out could be very different. (38:38)

In summary, Clay agrees we should take a fresh look at how much fat we’re feeding cows in basal diets and underlines the importance of the source of supplemental fatty acids. Bill concurs and commends Adam’s group for basically making cottonseed without fat in the low-fat basal diet, which allowed for very clean interpretations of the fatty acid supplement results. Adam underlines that we can feed higher fat diets, but the fatty acid profile of all of those ingredients we might use is going to be key. In addition to fatty acids in diets and supplements, de novo synthesis of milk fat from acetate is the other half of the equation. Bringing those together might be a strategy to keep up with genetic improvements and drive higher milk fat yield. (47:43)

You can find this episode’s journal club paper from JDS Communications here: https://www.sciencedirect.com/science/article/pii/S2666910223001114

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This Real Science Exchange podcast episode was recorded during a webinar from Balchem’s Real Science Lecture Series. You can find it at balchem.com/realscience.

Feeding rumen-protected choline in early lactation has consistently increased milk yield and energy-corrected milk yield, which is more pronounced when cows are fed diets low in metabolizable methionine. Choline feeding also increases milk fat and protein yield, minimizes body condition loss in early lactation, and reduces postpartum disease incidence. Dr. McFadden presents three topics about choline biology in the dairy cow. (01:45)

1. Why should we consider fatty acid feeding when feeding methyl donors like choline and methionine?
2. Choline degradation in the rumen and small intestine, focusing on the role of triethylamine oxide 
3. Why should we consider lysophosphatidylcholine as an immunomodulator in fresh cows and preweaning calves?

Fatty acid nutrition to optimize methyl donor efficiency. (4:02)

Fatty liver is a concern for fresh cows because of its relationship with ketosis, poor fertility and compromised milk production. Cows with fatty liver exhibit low circulating concentrations of phosphatidylcholine, which is a component of very low-density lipoproteins (VLDL) that transport triglycerides out of the liver. Feeding rumen-protected choline lowers liver triglyceride deposition by supporting the synthesis of phosphatidylcholine and thus, VLDL. 

Dr. McFadden goes on to explain the two different pathways for phosphatidylcholine in the liver and how those interact with fatty acid metabolism. He describes several experiments that have investigated how rumen-protected choline and supplemental fatty acids interact in lactating cows. 

Low phosphatidylcholine supply is a key feature of fatty liver in dairy cows, likely due to low polyunsaturated fatty acid (PUFA) and low choline supplies. Delivery of post-ruminal PUFA may support phosphatidylcholine synthesis with accompanying improvements in insulin sensitivity, body condition maintenance, and inflammation, but interactions with dietary fatty acid digestibility should be considered. Dr. McFadden gives a list of considerations for fresh cow diets incorporating fat and choline supplementation. 

Gastrointestinal choline degradation and trimethylamine N-oxide (TMAO)  (16:58)

Unprotected choline is almost totally degraded in the rumen. Microbes convert choline into trimethylamine (TMA) which is then converted to TMAO in the liver. Rumen-protected choline allows for a large proportion of choline to reach the small intestine intact. However, research shows that choline can also be degraded by microbes in the small intestine in the same pathway, limiting choline bioavailability. Plasma TMAO accumulation is associated with non-alcoholic fatty liver disease, inflammation, insulin resistance, obesity, oxidative stress, and cardiovascular disease in rodent and human models. Little research was available regarding if the relationship between TMAO and poor health was causative or just associative. Dr. McFadden’s lab infused cows intravenously with TMAO and found that TMAO did not modify milk production or glucose tolerance in early lactation cows. 

TMAO does not appear to influence energy metabolism or health in early lactation cows. Choline is subject to both ruminal and lower-gut degradation to TMA, and that influence on choline bioavailability needs to be defined. Data in non-ruminants suggests that unsaturated fatty acid feeding can shift the gut microbes to slow TMA formation. 

Lysophosphatidylcholine and immunomodulation (28:45)

Dr. McFadden gives an overview of neutrophil activation and the oxidative burst that contributes to pathogen killing. The ability to elicit the oxidative burst is diminished in pre-weaned calves and transition cows. When cows were given endotoxin to cause an immune response, circulating lysophosphatidylcholine was decreased. In rodent models, lysophosphatidylcholine promotes the oxidative burst and suppresses long-term inflammation in response to bacterial infection. Dr. McFadden cultured neutrophils from pre-weaned calves with lysophosphatidylcholine and observed an enhanced oxidative burst.

Immunosuppression is characterized by low circulating lysophosphatidylcholine concentrations in dairy cows. In  vitro data suggests lysophosphatidylcholine can activate neutrophils, and rumen-protected choline increases circulating lysophosphatidylcholine. Future research is likely to define an immunomodulatory role for choline. 

Dr. McFadden takes questions from the webinar audience. (38:07)

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Dr. Hernandez recently presented a Real Science Lecture series webinar on this topic. You can find the link at balchem.com/realscience.

Dr. Hernandez begins with an overview of how she came to study calcium metabolism in the mammary gland. Over the past number of years, she has worked on research to manipulate what’s happening in the mammary gland in the prepartum period to ensure adequate endocrine, nutritional, reproductive, and immunological status. (5:55)

The panelists discuss how “normal” has changed when it comes to transition cow health. Dr. Overton reminds listeners that 25 years ago, 6-8% of fresh cows in a herd having clinical milk fever was pretty typical. Now, we accept none of that. Subclinical hypocalcemia was not on the radar then, and we thought we had calcium all figured out. Dr. Hernandez’s work shows that this was not the case. She is pleased that a synergism of producers, veterinarians, and academics have been working together to understand the mechanisms of calcium metabolism to find solutions for individual farms based on their situation. (9:22)

Dr. Hernandez then discusses various interventions used in the industry, including low-potassium diets, negative DCAD diets, and zeolite clays. The clays are new to the US, and it seems that they work primarily through a phosphorus reduction mechanism and are best limited to feeding 10-14 days pre-calving. (18:14)

Dr. Overton asks Dr. Hernandez about a point in her webinar that cows are in negative calcium balance through 150-200 days in milk. She confirms that there are approximately 8.5 kilograms of calcium in the bones of a cow, but we don’t know how much of that she loses each lactation. Her dream scenario would be a CT scanner large enough to fit a dairy cow in to evaluate how her bones change throughout lactation. This leads to a discussion of whether or not we should be including higher rates of calcium in dairy cow diets. Dr. Hernandez would like to learn more about what’s happening with calcium absorption in the gut in real-time with endocrine status and stage of lactation, which is a challenging task. (23:17)

Co-host, Dr. Jeff Elliott, asks if the reason multiparous cows are more prone to milk fever is because they’re not as efficient at calcium resorption to the bone. Dr. Hernandez doesn’t have a definitive answer, but it could be due to less effective gut absorption with age, or it may be related to the influence of estrogen on bone density. She also mentions it could be endocrine-controlled or even stem cell-related.  (28:59)

Dr. Hernandez’s hypothesis has always been that you have to have a calcium decrease to trigger the negative feedback loop involved in calcium metabolism. Her advice is to wait until 48 hours to take a blood sample to analyze calcium. This aligns well with epidemiological research on the veterinarian side regarding delayed, persistent, transient, and normal hypocalcemic animals. (33:04)

Dr. Overton asks about a calcium-chelation study that Dr. Hernandez’s group conducted and whether or not chelating calcium had an impact on colostrum production. It did not in that experiment. Dr. Hernandez was surprised at how much chelating agent was needed to overcome the draw of the mammary gland, but that further underlines how much of a priority lactation is in metabolism. (41:45)

Scott asks both panelists their views on what the priority should be for research in this area. Dr. Hernandez’s ideas include more research on how zeolite clays work biologically, finding out what’s happening in the gut, mammary gland, and bone of a dairy cow at different stages of lactation. She emphasizes that research should be conducted at different stages rather than just extrapolating from one stage to another because lactation is incredibly dynamic. Dr. Overton seconded the idea of a better understanding of zeolite clays and their feeding recommendations, as well as research defining what happens to and where all the calcium is pulled from the bone during lactation. (45:32) 

In closing, Jeff, Tom, and Laura share their take-home thoughts. Jeff is excited to learn more about how zeolite clays work and if other products may come to the forefront to help in calcium metabolism management. Tom commends Laura on her work and how it has dovetailed so well with the epidemiological research from the veterinary side. Laura reminds listeners that the mammary gland is running the show and is thrilled that her work as a basic scientist is having an applied impact on the dairy industry. (51:17)

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Please note the recording was before the new NASEM model was released. However, there is still a lot of good information from Dr. Weiss beyond those recommendations. This Real Science Exchange podcast episode was recorded during a webinar from Balchem’s Real Science Lecture Series. You can find it at balchem.com/realscience.

Most ration formulation software uses the 2001 NRC mineral equations. The basic concept of the 2001 NRC mineral requirements is to feed enough absorbable minerals to maintain adequate labile body stores and fluid concentrations. Minerals are lost each day via excretion in feces and urine, milk production, and incorporation into tissues or the fetus in the case of growing or pregnant animals. We have decent data to predict mineral concentrations of milk, growth, and the fetus; however, the endogenous loss in feces is much harder to capture. Absorption coefficients (AC) for most minerals are exceedingly difficult to measure. (0:29)

The NRC requirements are the means of several experiments. Feeding to the mean results in half the cows being fed adequately or in excess, and half are not fed enough. In human nutrition, recommended daily allowances for vitamins and minerals are calculated as the mean plus two standard deviations, which statistically meets the requirement for 97% of the population. Since the standard deviation of the requirement is hard to acquire, human nutrition uses the same standard deviation for energy metabolism, around 20%. Dr. Weiss feels this is a reasonable safety factor for minerals for animals as well. He recommends feeding about 1.2 times the NRC requirement while keeping an eye on the maximum tolerable limit for the mineral in question. (4:59)

How do we measure absorption? We measure the minerals in the diet, we apply AC, and we get grams or milligrams of absorbed minerals available for the animal to use. Dr. Weiss details some of the complex methodology involved in trying to obtain AC. Feces contain not only unabsorbed dietary minerals but also endogenous/metabolic minerals (e.g., intestinal cells, enzymes, etc.) and homeostatic excretion of minerals (e.g., dumping excess minerals). In the 2001 NRC, the endogenous fecal for almost every mineral is a function of body weight, which is incorrect. It should be a function of dry matter intake. (8:40)

Endogenous fecal losses can also be measured using stable or radioactive isotopes. This method is extremely expensive and if radioactive isotopes are used, management of radioactive waste becomes an issue. Thus, most of the AC for trace minerals that used these methods are 50-60 years old. (15:33)

Dr. Weiss details some of the issues with calcium requirements in the 2001 NRC leading to overestimation of calcium absorption for many calcium sources and overestimation of the maintenance requirement due to endogenous fecal being calculated using body weight. Organic and inorganic phosphorus have different AC, so partitioning between organic and inorganic will give a more accurate estimate of the requirement. (16:33)

Potassium has a linear antagonistic effect on magnesium. You can feed more magnesium to overcome this antagonism, but you won’t ever eliminate it. If you feed a few percent added fat as long-chain fatty acids, Dr. Weiss recommends feeding 10-20% more magnesium to account for soap formation in the rumen. (19:17)

It’s much more difficult to measure AC for trace minerals due to multiple antagonists, interactions among different minerals, and regulated absorption. In addition, AC for trace minerals is very low, which means a small change in the AC can have a huge impact on diet formulation. All feeds in the NRC system have the same AC for each trace mineral and we know that’s not right.  (25:39)

Dr. Weiss gives an overview of different trace mineral antagonisms and interactions and details his approach to formulation if he has absorption data for a particular ingredient. He also gives his estimates of revised AC for several minerals. (28:07)

In summary, the factorial NRC approach only fits 50% of the population. Feeding an extra 10-20% above the NRC requirement includes about 97% of the population. We need to continue to account for more sources of variation in AC. Interactions need to be top of mind when considering mineral requirements and diet formulation. (37:39)

Dr. Weiss takes a series of questions from the webinar audience. (40:50)

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