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

The study, published in the journal Discover Agriculture by Erica Auguste of Trinidad and Tobago’s Ministry of Agriculture and Fisheries and colleagues Martin Hughes and Sivakumar Karuppusamy at the University of the West Indies, set out to answer a question with real economic stakes. Dairy farming across the tropics is dominated by smallholders, and their productivity is chronically low. In Trinidad and Tobago, national milk production collapsed from roughly 9.4 million kilograms in 2001 to about 1.6 million kilograms in 2024. Jamaica saw annual yields fall by around 57 percent over a comparable period. Understanding which biological factors actually constrain output on these farms is therefore not an academic exercise but a matter of livelihood and food security.

The Centeno Livestock Station occupies about 502 acres of flat to gently sloping land in El Carmen, St. Helena, in the county of Caroni. Its soils belong to the Cunupia series — heavy clays with impeded drainage and a pH between 4.5 and 5.4 — and the climate is classically tropical, with average annual rainfall near 1,877 millimetres and temperatures ranging from 22.7 to 31.3 degrees Celsius. A wet season runs from July to December and a dry season from January to June, during which pasture quality and quantity typically decline. The dairy herd of roughly 60 cows grazes rotationally on Brachiaria arrecta and unimproved native grasses, is milked twice daily with an automated system, and receives about 2.0 to 2.5 kilograms of an 18 percent crude protein concentrate at each milking.

Two breeds dominate the herd: the Centeno Crossbred, a Bos taurus × Bos indicus animal developed in the late 1970s by crossing Holstein-Friesians with Zebu-type breeds to combine high yield with heat tolerance and resistance to tick fever, and the Jersey. The researchers deliberately excluded a small group of graded Holstein-Friesians because so few were lactating and in poor condition. Breeding is carried out by artificial insemination, and the cows range from three to twelve years old. It was this herd, managed under consistent conditions, that provided the retrospective dataset spanning 2014 to 2019.

The team analysed the records using analysis of variance in SPSS version 27, treating calf sex, breed, parity and the breed-by-parity interaction as fixed effects, with Bonferroni-adjusted comparisons and Tukey’s test to separate means. Data normality was confirmed with the Ryan-Joiner test, and lactations shorter than 140 days in milk were excluded from total-yield calculations. Early lactation was defined as the first 90 days in milk. The statistical verdict was unambiguous: calf sex, breed and the breed-by-parity interaction had no significant effect on milk yield or lactation length.

Parity told a different story. Cows in their fourth through sixth parities produced 849 ± 66 kilograms of milk in early lactation, and those beyond their sixth parity produced 1,005 ± 116 kilograms — both figures significantly higher than the 673 ± 41 kilograms recorded for cows in their first to third parities. Daily milk yield followed the same gradient, at 5.6 ± 0.33 kilograms for the youngest parity group compared with 8.4 ± 1.0 kilograms for cows beyond their sixth lactation. The pattern makes physiological sense: young cows are still growing, so nutrients and energy must be split between body development, gestation and milk synthesis, often pushing them into a deeper negative energy balance. Mature cows, with larger mammary glands and more developed secretory tissue, can channel a greater share of their intake into milk.

Perhaps the most striking finding came from regression analysis. Early lactation milk yield accounted for 73 percent of the variability in total lactation yield — a coefficient of determination of 0.73. In other words, a cow’s output in her first three months of milking is a powerful predictor of her entire lactation. This aligns with a well-established body of literature showing that early lactation is a physiologically critical window in which milk yield peaks while energy demands often exceed dry matter intake. It also suggests that phase-specific management — concentrating feed resources and attention on freshly calved cows — could pay dividends even on smallholder, pasture-based tropical farms, where such approaches are rarely practised.

The null result on calf sex is notable because the literature on sex-biased milk synthesis is genuinely contested. Some studies, including a well-known analysis of Holsteins, reported that cows carrying female fetuses produced around 143 kilograms more milk than those carrying males, possibly because longer gestations for male calves shorten the subsequent lactation. Others found the opposite, attributing higher yields after male births to larger fetal size and elevated placental estrogen, which stimulates prolactin release — though bigger calves also raise the risk of difficult calvings that depress yield. The Centeno findings suggest that such sex effects, where they exist, are contingent on factors like calf size, dam health, parity and production system, and that within a uniform herd under consistent management, they may simply wash out.

The equivalence of the Jersey and Centeno Crossbred cows is equally consequential. Despite their different genetic backgrounds, the two breeds performed comparably under identical conditions, with the crossbreds posting numerically higher early lactation and daily yields while Jerseys showed numerically higher total yield and longer lactations. Since neither difference reached significance, the results hint that both breeds carry similar genetically linked performance characteristics when mature body size and management are held constant. For farmers choosing breeding strategies, that is reassuring: the locally adapted crossbred, bred for heat tolerance and disease resistance, gives up little in productive potential to the imported Jersey.

The sobering counterpoint is that absolute productivity at the station remains very low. Jersey cows elsewhere in subtropical climates yield around 11 kilograms of milk per day, and 20 to 25 kilograms in temperate environments — between 27 and 68 percent more than the CLS herd. Worryingly, low productivity in Centeno Crossbreds was flagged four decades ago, and the new data suggest performance may have declined further, pointing to persistent inadequate nutrition, unimproved pastures, dry-season feed gaps, costly concentrate supplementation and possible genetic depletion. The authors argue that improving pasture quality and quantity, supplemental feeding, reproductive efficiency and heat-stress management — measures that meta-analyses suggest can lift smallholder tropical milk yields by as much as 29 percent — must target cows in fourth and later parities and, above all, cows in early lactation, because that is where milk production is maximized and where the whole lactation is won or lost.

Subject of Research: Effects of calf sex, breed and parity on milk yield and lactation length in a tropical dairy herd

Article Title: Effects of calf sex, breed and parity on the lactation performance of dairy cows in Trinidad and Tobago

Article References: Auguste, E., Hughes, M., & Karuppusamy, S. (2026). Effects of calf sex, breed and parity on the lactation performance of dairy cows in Trinidad and Tobago. Discover Agriculture, 4(1), Article 295. https://doi.org/10.1007/s44279-026-00779-x

Image Credits: AI Generated

DOI: 10.1007/s44279-026-00779-x

Keywords: dairy cattle, milk yield, parity, calf sex, lactation length, early lactation, Centeno Crossbred, Jersey, smallholder farming, Trinidad and Tobago, tropical agriculture, animal breeding