The premise is deceptively simple. Goats are evolutionary intermediates between browsers and grazers, and studies show they can satisfy up to 60 percent of their nutritional needs from foliage when given the choice. Yet European husbandry guidelines recommend pasture access without requiring access to trees and shrubs. Fast-growing poplars and willows, cultivated widely in alley-cropping and short-rotation plantations across temperate latitudes, already serve as feed for sheep and cattle in New Zealand, China, North America, and parts of Europe. In Germany alone, roughly 6,600 hectares of short-rotation poplar and willow plantations yield about nine tonnes of woody dry mass per hectare annually, along with up to three tonnes of foliage per hectare in the second year after planting. Whether that foliage actually delivers usable nutrition to goats, however, had never been thoroughly tested.

The researchers ran two linked experiments. In the first, four castrated Saanen goat wethers, each about 1.5 years old, were rotated through four diets in a 4-by-4 Latin square design: meadow hay alone, or hay supplemented with 650 grams per day of dried foliage from one of three hybrids, black poplar (Populus nigra × deltoides), balsam poplar (P. nigra × maximowiczii), or willow (Salix triandra × viminalis). During the third week of each feeding block, the animals were moved into respiration chambers where oxygen consumption, carbon dioxide production, and methane emissions were measured at six-minute intervals, while feces and urine were collected for complete nutrient, energy, and mineral balance calculations.

The chemical analysis alone was enough to turn heads. Compared with hay, the tree leaves contained up to ten times higher concentrations of crude protein, minerals, phenols, and measurable antioxidant capacity. Black poplar leaves were particularly rich in calcium at 21.6 grams per kilogram of dry matter, roughly five times the hay content, along with markedly higher zinc, copper, iron, magnesium, and selenium. Willow leaves carried the highest manganese levels and, remarkably, showed antioxidant capacity six to ten times greater than hay in standard ABTS and FRAP assays. The foliage also packed condensed tannins and phenolic compounds at two to three times the hay concentrations, a double-edged property that would prove consequential later in the study.

Digestibility results favored the poplars. Balsam poplar diets achieved the highest organic matter digestibility at 64 percent, compared with 59 percent for hay and just 56.1 percent for willow. Willow fared worst across the board, posting the lowest crude protein digestibility at 52.9 percent and the lowest fiber digestibility, a deficit the researchers attribute to its extraordinary condensed tannin content of 116.6 grams per kilogram of dry matter, some 22-fold higher than the poplar leaves. Tannins bind proteins and nutrients in the rumen, forming complexes that resist digestion and inflate fecal nitrogen losses. Despite this, microbial protein production in the rumen, estimated from urinary purine derivatives, was unaffected by any of the foliage diets.

Perhaps the most climate-relevant finding was what came out of the animals as gas. Methane emitted per kilogram of dry matter intake was significantly lower on all three foliage diets than on hay, with willow delivering the largest reduction at 17.2 grams per kilogram versus 22.4 for hay. Tannins suppress methanogenic archaea in the rumen, and the bacteriostatic effect appears to translate directly into reduced enteric methane, the potent greenhouse gas that accounts for a substantial share of livestock agriculture’s climate footprint. Notably, foliage feeding raised no red flags for food safety: despite leaves accumulating more zinc, manganese, nickel, and lead than hay, plasma concentrations of these heavy metals in the goats remained indistinguishable from hay-fed controls.

Selenium told a subtler story. Although balsam poplar leaves contained the most selenium, wethers fed the black poplar diet showed the highest plasma selenium at 72.6 micrograms per liter, significantly above both the balsam poplar and hay groups. Because selenium intake differed only marginally between the two poplar diets, the authors conclude that selenium from black poplar is more bioavailable, possibly reflecting differences between inorganic and organic selenium species in the leaves. This bioavailability advantage carried into the second experiment, where lactating does supplemented with black poplar foliage consumed 2.7 times more selenium and maintained significantly higher plasma selenium concentrations by the fifth week of lactation, hinting that tree foliage could partly substitute inorganic selenium supplements derived from fossil sources.

That second experiment put the most promising candidate to a real-world test. Sixteen pregnant, year-old Saanen goats were split after lambing: half received 700 grams per day of black poplar foliage alongside hay and wheat during the first five weeks of lactation, while the control group received hay and wheat only. The hypothesis was logical, even elegant. The periparturient period imposes crushing energy and calcium demands for fetal growth, colostrum, and milk production, driving negative mineral balances, body fat mobilization, and oxidative stress. Poplar leaves are loaded with calcium, selenium, and polyphenolic antioxidants, precisely the profile that might buffer these stresses.

The results dismantled that hope. Poplar-supplemented does showed no improvement in glutathione peroxidase activity or any other antioxidant marker, despite the leaves’ impressive laboratory antioxidant capacity, suggesting the phenolic compounds were poorly absorbed in vivo. Worse, in the second week after lambing the poplar group exhibited significantly lower serum calcium concentrations and a lower ratio of osteocalcin to CTX, the molecular signatures of bone formation and resorption, indicating intensified bone mobilization. The likely culprit is tannin chemistry: condensed tannins are known to hinder intestinal calcium absorption, and calcium actually enhances the binding between tannins and proteins, compounding the interference. The poplar does were losing more calcium from skeleton despite consuming nearly two and a half times more dietary calcium than controls.

The study’s authors draw a cleanly practical conclusion. Black poplar foliage is a genuinely valuable feed for non-lactating goats, offering improved protein digestibility, selenium status, and reduced methane yield, but it should not be fed to goats in early lactation, when calcium homeostasis is already stretched to its limit. The team acknowledges limitations, including small animal numbers that limited statistical power for mineral balances and methane measurements, and the well-documented sensitivity of leaf composition to harvest time, leaf age, soil, and climate. Still, in an era when agriculture urgently seeks feed resources that cut emissions without competing for cropland, the image of a goat stripping leaves from a poplar row has gained real scientific weight, provided farmers know exactly when in the reproductive calendar to open the gate.

Subject of Research: Nutritional value of poplar and willow foliage in goat diets and its effects on digestibility, selenium status, methane emission, and calcium metabolism around lambing

Article Title: Nutrient and energy digestibility, mineral status and antioxidant defense in goat wethers and periparturient does supplemented with poplar and willow leaves

Article References: Helffenstein, K., Schwerdtfeger, J., Görs, S., Durkalec, M., Kowalczyk, J., Eggert, A., Wilkens, M. R., & Kuhla, B. (2026). Nutrient and energy digestibility, mineral status and antioxidant defense in goat wethers and periparturient does supplemented with poplar and willow leaves. Frontiers in Animal Science, 7, Article 1861647. https://doi.org/10.3389/fanim.2026.1861647

Image Credits: AI Generated

DOI: 10.3389/fanim.2026.1861647

Keywords: goats, poplar foliage, willow, agroforestry, selenium, methane emissions, tannins, calcium metabolism, antioxidants, animal nutrition, early lactation, digestibility

Researchers at the University of Veterinary Medicine in Vienna, working with the Agricultural Research and Education Center Raumberg-Gumpenstein in Austria, followed 66 Fleckvieh, Holstein-Friesian, and New Zealand Friesian cows and heifers through 85 calvings between November 2022 and March 2024. Blood samples were collected at a dense series of time points: roughly 21, 14, and 7 days before the expected calving date, just hours before and after parturition, and then at 1, 3, 7, and 14 days postpartum. From each sample, the team measured serum total calcium alongside a panel of osteoimmunological markers, proteins and enzymes that reflect the ongoing dialogue between the immune system and bone tissue.

The central focus was the RANK/RANKL/OPG signaling system, a triad of molecules from the tumor necrosis factor superfamily that governs bone remodeling. RANK ligand, produced by osteoblasts and activated T cells, binds to the RANK receptor on osteoclast precursor cells and drives their differentiation into mature bone-resorbing cells. Osteoprotegerin acts as a soluble decoy receptor, neutralizing RANKL and thereby restraining osteoclast formation. This regulatory axis responds to hormonal and cytokine signals, including interleukin-6, tumor necrosis factor-alpha, and interleukin-17, which are known to shift during the inflammatory events of pregnancy and calving. Because parturition itself is an inflammatory process, involving detachment and expulsion of the fetal membranes, the researchers reasoned that immune activation around calving might perturb bone turnover and influence systemic calcium availability.

To track bone resorption directly, the team measured C-terminal cross-linked telopeptide of type I collagen, or CTX-I, a fragment released when type I collagen is degraded, widely accepted as a sensitive marker of osteoclastic activity in both human and veterinary medicine. They also measured osteocalcin, a marker of osteoblast formation activity, and alkaline phosphatase, an enzyme long used in human medicine to evaluate bone diseases such as osteomalacia and Paget’s disease. After calving, cows were retrospectively classified by their serum calcium concentrations as normocalcemic, above 2.20 millimoles per liter; subclinical hypocalcemic, between 1.80 and 2.20; or low-calcium, below 1.80 millimoles per liter.

The distribution of calcium status revealed how widespread the problem is even in a well-managed research herd. Of the 85 calvings, only about 39 percent remained normocalcemic, while 54 percent fell into the subclinical hypocalcemic range and 7 percent into the low-calcium category. Notably, the burden fell disproportionately on older animals: among cows in their fourth or later lactation, 18 of 27 calvings were subclinical and 5 were frankly low-calcium, whereas most heifers maintained normal calcium concentrations.

CTX-I emerged as the standout marker. Its concentrations rose after parturition, peaked in early lactation, and then gradually declined, consistent with a transient stimulation of bone resorption to meet the demands of lactation. Crucially, first-lactation animals showed significantly higher CTX-I concentrations than multiparous cows at every examination time, and cows that went on to develop low calcium had the lowest CTX-I concentrations at nearly all time points, with significant differences from normocalcemic cows stretching from two weeks before calving through two weeks after. The interpretation is striking: cows that could not mobilize calcium from their skeletons effectively were the ones that became hypocalcemic, and their impaired resorptive capacity was visible in the blood before calving.

The predictive power was quantified using receiver operating characteristic analysis, which evaluates how well a biomarker separates two groups across all possible threshold values. Prepartum CTX-I achieved area under the curve values between 0.75 and 0.90, with Youden indices between 0.75 and 0.82 at several time points. At 14 days before calving, a cut-off of 0.17 nanograms per milliliter yielded 100 percent specificity and roughly 81 percent sensitivity for identifying cows that would later become hypocalcemic. In practical terms, a single blood test in late gestation could flag most at-risk cows while essentially never falsely accusing a cow that would remain healthy. Alkaline phosphatase showed moderate predictive value before calving, and RANK, whose concentrations declined in all parity groups before calving and then remained low, was more useful for tracking postpartum regulatory processes than for prepartum prediction. No reliable models could be built for osteocalcin, RANKL, or osteoprotegerin, likely because RANKL and OPG act predominantly within the local bone microenvironment and are not fully reflected in circulating concentrations.

The parity findings carry their own biological weight. The consistently lower CTX-I concentrations in older cows suggest an age-related decline in bone remodeling, echoing human studies showing that osteoclast precursors become less responsive to RANKL stimulation with age. This diminished capacity to activate osteoclast-mediated calcium mobilization offers a mechanistic explanation for why older cows are far more susceptible to milk fever: when the sudden calcium drain of lactation begins, their skeletons simply cannot respond as vigorously as those of younger animals. Markers of bone formation, by contrast, showed far less pronounced age-related variation, indicating that the parity effect is concentrated on the resorptive side of skeletal metabolism.

The authors are careful to frame the findings appropriately. The low-calcium group contained only six calvings, limiting statistical power, and the study was conducted under specific herd and management conditions without controlled nutritional factors, which are known to influence calcium metabolism. The commercial ELISA kits used may introduce analytical variability, and the observational design precludes causal inference. The proposed cut-off values require validation in independent cohorts before any clinical application, and the researchers explicitly caution that biomarker screening should complement, not replace, established herd-level prevention strategies such as dietary calcium management around calving.

Even with those caveats, the study opens a genuinely new window on an old problem. Milk fever has been managed for decades through nutritional strategies, yet individual risk prediction has remained crude. The demonstration that a bone resorption marker measured weeks before calving can identify cows destined for hypocalcemia suggests that the disease process begins long before the calcium crash, rooted in the skeleton’s diminished ability to respond. If validated at scale, CTX-I testing in late gestation could allow farmers and veterinarians to target preventive interventions precisely at the cows that need them most, turning a metabolic emergency into a manageable prediction problem.

Subject of Research: Osteoimmunological biomarkers for predicting periparturient hypocalcemia in dairy cows

Article Title: Periparturient changes in osteoimmunological markers and their association with hypocalcemia in dairy cows

Article References: Gleissenberger, J., Gleissenberger, M., Becker, S., Schraml, M., Eingang, D., Khol, J. L., & Wittek, T. (2026). Periparturient changes in osteoimmunological markers and their association with hypocalcemia in dairy cows. Journal of Veterinary Internal Medicine, 40(5), Article aalag244. https://doi.org/10.1093/jvimsj/aalag244

Image Credits: AI Generated

DOI: 10.1093/jvimsj/aalag244

Keywords: dairy cows, hypocalcemia, bone resorption, CTX-I, RANK/RANKL/OPG, osteocalcin, alkaline phosphatase, transition period, milk fever, osteoimmunology, biomarkers, veterinary medicine