Researchers tested whether feeding cattle a tropical plant called Leucaena would damage their thyroid glands and change how their bodies use energy. The plant contains a compound called mimosine that scientists worried might be harmful. Six young bulls ate different amounts of this plant for over a month while scientists measured their thyroid hormones, oxygen use, and energy levels. Surprisingly, the plant didn’t hurt their thyroid function or change how much energy their bodies needed. This is good news for farmers in tropical areas who want to use this affordable plant as cattle feed.

The Quick Take

  • What they studied: Does feeding cattle a tropical plant called Leucaena damage their thyroid glands or change how their bodies use energy?
  • Who participated: Six young male Brangus cattle (a beef breed) averaging about 685 pounds each, around 20 months old. Each animal was tested three different times eating different amounts of the plant.
  • Key finding: Even when cattle ate high amounts of Leucaena (up to 60% of their diet), their thyroid hormone levels stayed normal and their energy use didn’t change. The plant didn’t harm them the way scientists expected.
  • What it means for you: If you raise cattle in warm climates, Leucaena appears to be a safe, affordable feed option. However, this study was small and only looked at young bulls, so more research on different types of cattle and longer feeding periods would be helpful.

The Research Details

Scientists designed this as a crossover study, meaning each of the six bulls ate all three different diets at different times. This design is strong because it lets researchers compare how the same animal responds to different treatments. The study lasted 34 days per diet: 14 days for the cattle to get used to the new food, then 20 days of careful measurements. During the measurement period, scientists kept the bulls in special cages and used equipment that measured the gases they breathed out (oxygen, carbon dioxide, and methane) to calculate how much energy their bodies were using.

This research approach is important because it directly measures how cattle bodies process energy, rather than just guessing. By using special breathing chambers and blood tests, scientists could see exactly what was happening inside the animals. The crossover design is particularly strong because it reduces confusion from differences between individual animals.

This study has some strengths: it used careful scientific measurements of breathing gases and blood hormones, and it tested each animal multiple times. However, there are limitations: only six bulls were tested (a small number), they were all young males of one breed, and the study only lasted about a month per diet. Longer studies with more animals and different types of cattle would give stronger evidence.

What the Results Show

The main finding was surprising: thyroid hormone levels (T3 and T4) didn’t change at all, even when cattle ate the highest amount of Leucaena. Scientists had expected the mimosine compound in the plant to lower these hormones, but it didn’t happen in this study. Similarly, when researchers measured how much oxygen the cattle breathed and how much methane they produced, these measurements were the same whether the bulls ate the plant or not. This means their bodies were using energy at the same rate regardless of the diet. The amount of energy the cattle needed to maintain their body weight also stayed constant across all three diets, averaging about 408 kilojoules per kilogram of body weight per day.

One interesting finding was that cattle eating the highest amount of Leucaena lost more energy in their feces (manure). This means their bodies couldn’t digest and absorb as much of the plant material. However, this didn’t translate into the cattle having less usable energy overall, because they compensated by eating slightly more. The energy they could actually use (metabolizable energy) was similar across all diets.

Previous research had suggested that mimosine, the compound in Leucaena, could lower thyroid hormones in cattle. This study didn’t confirm that finding, which is interesting. One possible explanation is that the cattle in this study were only eating maintenance-level diets (just enough to maintain their weight), not growing diets. It’s possible that thyroid effects might show up differently when cattle are actively gaining weight. The results suggest that at maintenance feeding levels, Leucaena is safer than previously thought.

This study has several important limitations. First, only six bulls were tested, which is a small number—larger studies give more reliable results. Second, all the cattle were young males of one breed, so results might differ for females, older cattle, or other breeds. Third, the study only lasted about a month per diet, so we don’t know what happens with very long-term feeding. Fourth, the cattle were kept in cages during measurements, which is not their normal environment. Finally, this study only looked at cattle at maintenance weight; growing cattle might respond differently.

The Bottom Line

Based on this research, Leucaena appears to be safe to feed cattle at levels up to 60% of their diet (moderate confidence). Farmers in tropical regions where this plant grows can consider using it as a cost-effective feed source. However, start with lower amounts and monitor your cattle’s health and weight gain. This recommendation applies mainly to cattle at maintenance weight; growing cattle may need additional study.

This research matters most for farmers in tropical and subtropical climates where Leucaena grows naturally or can be grown cheaply. It’s particularly relevant for beef cattle operations looking to reduce feed costs. This study specifically looked at young bulls, so results may vary for dairy cattle, breeding females, or older animals. If you’re in a temperate climate, this plant may not be practical for your operation.

If you start feeding Leucaena to your cattle, you should see stable weight and normal thyroid function within 2-3 weeks. However, this study only measured short-term effects (about a month), so long-term effects over months or years aren’t yet known. Monitor your cattle regularly for any changes in health, appetite, or weight gain.

Want to Apply This Research?

  • If using Leucaena as cattle feed, track weekly body weight and body condition score (a 1-9 scale of how thin or fat the animal looks). Also note feed intake and any visible health changes. Compare these metrics to cattle on your standard diet to ensure performance is similar.
  • For farmers considering Leucaena: start by replacing 20-30% of regular feed with Leucaena for one group of cattle while keeping a control group on standard feed. Use the app to log daily observations, weight changes, and any health issues. This lets you safely test whether it works for your specific cattle and climate.
  • Set up monthly check-ins to compare cattle on Leucaena versus standard feed. Track: body weight, body condition, feed costs, overall health, and any digestive issues. If cattle perform equally well while costing less to feed, gradually increase Leucaena inclusion. If problems appear, reduce the amount or stop using it.

This research is specific to young male Brangus cattle at maintenance feeding levels and may not apply to all cattle types, ages, or production stages. Always consult with a veterinarian or animal nutritionist before making major changes to your cattle’s diet. Individual animals may respond differently than the group average shown in this study. This study was conducted over a short time period (one month per diet), so long-term safety cannot be guaranteed. If your cattle show any signs of illness, reduced appetite, or poor performance after dietary changes, contact a veterinarian immediately.