Role of dietary phosphorus in hypocalcemia
New research from the University of Wisconsin analyzes three different close-up feeding strategies for their blood calcium and production outcomes
By Meghan Connelly, Ph.D., Protekta
Hypocalcemia, or low blood calcium, is a disease that affects transition cows and can result in a variety of other diseases, in addition to the commonly known “down cow” disorder. Hypocalcemia can range from the clinical manifestation known as milk fever to a subclinical occurrence evinced by low blood calcium but no outward indication of the disease. Despite the vast improvements made in the industry, managing clinical milk fever, subclinical hypocalcemia and “milk fever breaks” still remain. This has resulted in continual investigation of alternative pre-fresh nutrition strategies to mitigate clinical and subclinical hypocalcemia.
In a new study done at the University of Wisconsin-Madison by Frizzarini et al. (2024)*, researchers compared three close-up diets: one with synthetic zeolite A, a negative dietary cation-anion difference (-DCAD) diet and a positive DCAD diet (control) and their implications on blood calcium and performance. This study resulted in two publications, both of which were recently published in the Journal of Dairy Science. Dr. Laura L. Hernandez, professor at the University of Wisconsin-Madison, was the lead investigator of the research.
The study included 121 multiparous Holstein cows, blocked by lactation number and expected due date. The cows were randomly assigned to one of the three prepartum diets: control (+190 mEq/kg; n = 40), -DCAD (−65 mEq/kg; n = 41), or the control diet supplemented with synthetic zeolite A (synthetic zeolite A; +278 mEq/kg, fed at 3.3% DM, 500 g/day; n = 40).
In Part 1, researchers evaluated the effects of the three diets on peri-partal mineral metabolism. A few of the mineral metabolism metrics Frizzarini and colleagues analyzed were blood calcium, blood phosphorus and fecal phosphorus. The results showed that cows fed synthetic zeolite A and -DCAD diets pre-fresh had higher blood calcium concentrations compared to control fed cows. Interestingly, cows fed synthetic zeolite A exhibited the highest blood calcium concentrations pre-partum and on the immediate days following calving (D0, D1, and D2) relative to cows fed a -DCAD or control diet.
Consistent with previously published research results, not only did cows fed synthetic zeolite A have higher blood calcium concentrations during the transition period, but synthetic zeolite A fed cows had lower blood phosphorus concentrations relative to all other treatments. In addition to the reduced blood phosphorus, cows fed synthetic zeolite A had decreased salivary phosphorous concentrations and increased fecal water extractable phosphate suggesting a phosphorus restriction. Despite seeing dramatic differences in blood calcium, parathyroid hormone, a potent calcium homeostasis hormone, was unaffected by diets but increased at parturition in all treatments.
“The data from feeding zeolite A indicate that the improvement in blood calcium concentrations pre and postpartum most likely is regulated by a dietary phosphorous restriction,” concluded Frizzarini and colleagues.
In Part 2, the team continued to assess the effects of feeding the same three close-up diets (synthetic zeolite A, -DCAD and the control diet) on dry matter intake (DMI), energy metabolism, and colostrum and milk production. In this companion paper, researchers measured daily prepartum DMI, daily rumination, colostrum quality and quantity, daily milk production and supplemental blood work to evaluate energy metabolism.
The results of Part 2 demonstrated that feeding synthetic zeolite A reduced DMI and rumination pre-partum relative to -DCAD and control diets, but no differences were observed in rumination postpartum. Postpartum DMI was not collected. Also, there was no difference due to diet on blood glucose, β-hydroxybutyrate (BHB) concentrations, or body fat mobilization postpartum.
Colostrum yield and BRIX score did not differ between dietary treatments; however, colostrum collected from cows fed synthetic zeolite A had the highest IgG concentrations (91.10 ± 2.63, 78.00 ± 2.63, and 78.90 ± 2.63 mg/ mL for synthetic zeolite A, control and -DCAD, respectively). Results also showed that synthetic zeolite A-fed cows in their third or greater lactation had the highest milk production (51.0 ± 1.1 kg) during the first 49 days in milk compared to cows fed -DCAD or control diets.
“This study demonstrates that despite a decrease in DMI and rumination in cows fed zeolite A pre-partum, blood BHB concentrations were not altered,” stated Frizzarini and colleagues. “Additionally, cows fed zeolite A had higher colostral IgG concentrations, and third or greater lactation cows fed zeolite A produced the most milk. These data suggest that feeding zeolite A prepartum may improve colostrum quality and improve milk yield in mature cows and does not impact energy metabolism.”
References
J Dairy Sci. (March 13, 2024) Mechanisms by which feeding synthetic zeolite A and a dietary cation-anion difference diets impact mineral metabolism in multiparous Holstein cows: Part 1 https://www.journalofdairyscience.org/article/S0022-0302(24)00546-0/fulltext
J Dairy Sci. (March 13, 2024) Mechanisms by which feeding synthetic zeolite A and a dietary cation-anion difference diets impact feed intake, energy metabolism and milk performance: Part 2 https://www.journalofdairyscience.org/article/S0022-0302(24)00547-2/fulltext