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04 Jun 2025

Anionic Diets and Transition Cow Health with Dr. Pedro Melendez

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Moderate anionic diets: key to preventing hypocalcemia in dairy cows — Insights from Dr. Pedro Melendez

nutriNews International had the opportunity to sit down with Dr. Pedro Melendez as part of our nutriInsights segment, where we meet with leading experts in dairy nutrition and animal health. In this comprehensive interview, Dr. Melendez shares his valuable expertise on the use of anionic diets to prevent hypocalcemia—a common and costly metabolic disorder—in dairy cows during the critical transition period around calving. His practical and evidence-based approach highlights the importance of moderate acidification, precise monitoring, and holistic herd management to improve outcomes for both cows and their calves.

Understanding anionic diets and calcium balance

Dr. Melendez explains that anionic diets work by introducing negatively charged minerals such as chloride and sulfate, which create a mild metabolic acidosis in the cow’s body. This subtle acidification increases the sensitivity of parathyroid hormone (PTH) receptors, which in turn enhances calcium mobilization from bones and improves calcium absorption in the intestines—both vital mechanisms to maintain proper calcium balance and prevent hypocalcemia during the high-demand period of calving and early lactation.

However, Dr. Melendez stresses the critical importance of moderation in acidification. The ideal prepartum urine pH should fall between 6.0 and 6.8, indicating a balanced, moderate acidification. He emphasizes that urine pH measurement is the most practical and reliable indicator of the diet’s effectiveness in achieving this balance, far outweighing reliance on theoretical Dietary Cation-Anion Difference (DCAD) values.

Dr. Melendez strongly warns against over-acidification (urine pH below 6.0), explaining its detrimental effects which include:

Reduced dry matter intake, as cows eat less when they become overly acidotic.

Increased incidence of displaced abomasum, a painful digestive disorder.

Higher rates of stillbirths, with studies showing a significant increase in calves lost when urine pH is too low.

Altered metabolic profiles, particularly decreased phosphatidylcholine, which is crucial for liver function and cell membrane integrity.

Impaired colostrum production, with reports of cows producing almost no colostrum when urine pH drops too low.

Negative impacts on calf health and birth weight, with calves born from over-acidified dams weighing less and showing signs of acidosis and reduced alertness.

Balancing nutrition with cow comfort and management

Beyond nutrition alone, Dr. Melendez highlights that cow comfort and environmental management are essential components for success.

He states, “Nutrition without cow comfort doesn’t work,” emphasizing that factors such as heat stress management, comfortable lying surfaces, feed freshness, and availability dramatically influence dry matter intake and overall health. Without these management elements in place, even the best-formulated diets may fail to produce the desired outcomes.

Evolving views on calcium supplementation

Dr. Melendez also discusses recent advances in understanding hypocalcemia classifications—transient, persistent, and delayed—and their implications for calcium supplementation strategies. While transient hypocalcemia within the first 48 hours postpartum may be a natural and possibly beneficial state, persistent or delayed hypocalcemia requires intervention.

He supports the use of calcium boluses at calving, particularly for older cows (3 or more lactations), who are at higher risk of subclinical hypocalcemia due to decreased PTH receptor sensitivity with age. Dr. Melendez is actively researching the optimal timing and combination of calcium supplementation with vitamin D to enhance calcium absorption and reduce the risk of hypocalcemia-related complications.

Looking ahead: maternal acid-base balance and calf health

Preliminary research presented by Dr. Melendez suggests that extreme maternal over-acidification may negatively affect calf development, resulting in calves born smaller, acidotic, and less responsive after birth. This potentially impairs their ability to absorb colostrum efficiently, even under good management. This area remains a critical focus for ongoing research aimed at protecting both dam and offspring health.

Watch or listen to the full nutrInsights interview with Dr. Pedro Melendez

For a deeper dive into these essential topics and practical recommendations, watch the full interview on nutriNews International’s YouTube channel or listen on the Agrinews Play podcast. Join us as we explore the science behind anionic diets, calcium management, and holistic strategies that help producers improve transition cow health and reduce costly metabolic diseases.