When pregnant cows don’t get enough food, their babies can be born smaller and weaker. Scientists wondered if giving pregnant cows a supplement called melatonin (a natural substance that helps with sleep) could help. They studied 29 pregnant cows, some fed normally and some fed less food. Half of each group got melatonin pills. Researchers found that melatonin changed how the placenta (the organ that feeds the baby) worked, especially when cows weren’t eating enough. The supplement seemed to help balance certain nutrients the baby received, though it didn’t fix all the problems caused by not eating enough.
The Quick Take
- What they studied: Whether giving pregnant cows a melatonin supplement could help their babies get better nutrition when the mothers weren’t eating enough food during pregnancy.
- Who participated: 29 young female beef cattle (called heifers) in their last few months of pregnancy. They were divided into four groups: normal food with no supplement, normal food with melatonin, restricted food with no supplement, and restricted food with melatonin.
- Key finding: Melatonin changed how the placenta transported fatty acids (important nutrients) to the baby, especially in cows that weren’t eating enough. Some fatty acids in the baby’s blood improved with melatonin, while others didn’t change much.
- What it means for you: For cattle farmers, this suggests melatonin might help protect developing calves when pregnant cows can’t eat enough during late pregnancy. However, melatonin alone didn’t completely fix all the nutritional problems caused by restricted feeding, so proper nutrition remains most important.
The Research Details
Scientists studied 29 pregnant cows from day 160 to day 240 of pregnancy (the last three months). They split the cows into two feeding groups: one group ate the normal amount of food recommended by nutrition experts, while the other group ate only 60% of that recommended amount. Within each feeding group, half the cows received 20 milligrams of melatonin (a natural substance) daily, while the other half received nothing.
At day 240 of pregnancy, all the cows had surgery to deliver their calves early so researchers could collect samples. They took blood samples from both the mother and baby calf, and also collected samples from the placenta (the organ that connects mother to baby and transfers nutrients). They measured the types and amounts of fatty acids in these samples and examined which genes were active in the placenta’s nutrient-transporting cells.
This approach allowed researchers to see exactly how melatonin affected the placenta’s ability to move nutrients to the developing calf, and whether those nutrients actually reached the baby.
Understanding how the placenta works is crucial because it’s the only way a developing calf gets nutrients. When pregnant cows don’t eat enough, the placenta may not work as well, and the calf might not grow properly. By studying the placenta’s genes and the actual nutrients reaching the calf, researchers can understand whether supplements like melatonin truly help or just seem to help.
This study had a relatively small number of animals (29), which means results should be confirmed with larger studies. The researchers used surgical delivery to collect precise samples, which is more reliable than other methods. They measured multiple types of fatty acids and looked at gene expression in the placenta, showing they examined the problem from multiple angles. However, because this was done in cattle, results may not apply to other animals or humans.
What the Results Show
When cows didn’t eat enough food, their blood contained higher levels of certain fatty acids (monounsaturated fats and omega-3 fats) compared to cows eating normally. Interestingly, melatonin didn’t change the mother cow’s fatty acid levels, whether she was eating normally or eating less.
The baby calves showed different results. When mothers ate restricted food without melatonin, babies had higher levels of omega-6 fatty acids. However, when melatonin was added, this increase didn’t happen—the babies’ omega-6 levels stayed similar to calves from normally-fed mothers. This suggests melatonin helped balance this particular nutrient.
The placenta itself showed the biggest changes. In cows eating restricted food without melatonin, certain genes that help transport nutrients were less active. When melatonin was added, some of these genes became more active again, especially in one part of the placenta. This means melatonin helped the placenta work better at moving nutrients to the baby.
Researchers found that a specific type of fatty acid called C16:0 behaved unusually. When mothers ate less food, they had more of this fatty acid in their blood, but the amniotic fluid (the fluid surrounding the baby) had less of it. This suggests the placenta wasn’t transferring this nutrient well during food restriction. Additionally, branch-chain fatty acids (a special type of fat) were lower in the amniotic fluid when mothers ate restricted food, and melatonin didn’t fix this problem. However, melatonin did increase branch-chain fatty acids in the baby’s blood when mothers ate normally.
Previous research showed that melatonin could increase birth weight in calves and reduce cellular stress before birth. This new study goes deeper by showing how melatonin actually works—by changing the placenta’s ability to transport nutrients. The findings confirm that melatonin helps, but also show it works differently depending on whether the mother is eating enough food or not. This explains why melatonin isn’t a complete solution to nutrient restriction.
The study included only 29 cows, which is a small number. Results might be different with more animals. The study was done in beef cattle, so findings may not apply to dairy cattle or other animals. Researchers only looked at one dose of melatonin (20 mg daily), so they don’t know if higher or lower doses might work better. The study ended at day 240 of pregnancy, so researchers couldn’t see if these changes affected the calves after birth or how they grew up.
The Bottom Line
For cattle farmers: If pregnant cows must eat restricted diets during late pregnancy, adding melatonin supplementation (20 mg daily) may help protect the developing calf’s nutrition, particularly for certain fatty acids. However, melatonin should not replace proper nutrition—ensuring pregnant cows eat adequate food remains the most important step. Confidence level: Moderate (based on one study with a small number of animals).
Cattle farmers and ranchers should care about this research, especially those who sometimes must reduce feed during late pregnancy due to drought, cost, or other challenges. Veterinarians advising on cattle nutrition may find this helpful. This research is less relevant to people raising other types of animals or those with abundant feed resources.
Changes in the placenta and fetal nutrients happened within weeks (the study measured effects from day 160 to day 240 of pregnancy). If farmers started melatonin supplementation in the last three months of pregnancy, they might see benefits in calf health at birth. Long-term effects on calf growth after birth would need additional research.
Want to Apply This Research?
- For farmers using a livestock app: Track daily melatonin supplementation (yes/no), maternal body condition score (1-9 scale), and estimated feed intake as a percentage of recommended amounts. Record calf birth weight and vigor score at birth to monitor outcomes.
- If using a farm management app, set daily reminders to administer melatonin to pregnant cows during the last three months of pregnancy. Log feed amounts given versus recommended amounts to ensure you’re meeting nutritional targets. Use the app to alert you if any pregnant cow drops below 80% of recommended feed intake.
- Create a long-term tracking system that records: (1) which pregnant cows received melatonin and which didn’t, (2) their feed intake levels, (3) calf birth weights and health scores, and (4) calf growth rates through weaning. Compare outcomes between supplemented and non-supplemented groups to see if melatonin made a practical difference on your farm.
This research was conducted in cattle and may not apply to other animals or humans. Melatonin supplementation should not replace proper nutrition during pregnancy—adequate feed intake remains essential. Before starting any supplementation program for livestock, consult with a veterinarian or animal nutritionist who understands your specific situation. This summary is for informational purposes and should not be considered veterinary or nutritional advice. Results are from one study with a small number of animals and should be confirmed by additional research before making major management decisions.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.