Gram Research analysis shows that nursing beef cows with abundant grass eat significantly more food and become more selective eaters compared to cows with limited grass. In a two-year study of 34 lactating cows, those with high grass availability ate 1.3 to 3.7 kilograms more per day and took smaller, more selective bites, suggesting they could choose higher-quality plants when grass was plentiful.
When nursing cows have access to more grass, they eat more food and change how they graze, according to a new study. Researchers watched 34 lactating beef cows in South America and found that cows with plenty of grass available ate 1.3 to 3.7 kilograms more per day than cows with limited grass. The cows with more grass also became pickier eaters, spending less time chewing each mouthful. This research helps farmers understand how to manage pastures better during the critical weeks after cows give birth, when they need extra nutrition for milk production.
Key Statistics
A two-year study of 34 lactating beef cows found that those with high grass availability (5 kg dry matter per 100 pounds body weight) ate 1.3 kilograms more food per day in year one and 3.7 kilograms more in year two compared to cows with limited grass availability.
Research on 34 nursing beef cows showed that cows with abundant grass took significantly fewer bites per feeding station (9 versus 13 bites), indicating more selective foraging behavior when grass was plentiful.
In a two-year study of lactating beef cows grazing subtropical grasslands, cows with limited grass availability showed increased chewing time relative to food intake in the second year, suggesting behavioral adaptation to extract maximum nutrition from scarce forage.
The Quick Take
- What they studied: How the amount of available grass affects the eating behavior and food intake of nursing beef cows during the first 40 days after giving birth.
- Who participated: 34 lactating beef cows in subtropical grasslands, studied over two years. The cows were divided into two groups: one with high grass availability (5 kg per 100 pounds of body weight) and one with low grass availability (3 kg per 100 pounds of body weight).
- Key finding: Cows with more grass available ate significantly more food (1.3 to 3.7 kg extra per day) and became more selective about which plants they ate, taking smaller bites and spending less time chewing each mouthful.
- What it means for you: Farmers can increase milk production and cow nutrition by ensuring adequate grass availability during the critical lactation period. However, this study focused on one specific climate and grass type, so results may vary in other regions.
The Research Details
Researchers conducted this study over two years in subtropical grasslands, observing 34 nursing beef cows divided into two groups based on grass availability. One group had high grass availability (5 kg of dry matter per 100 pounds of body weight daily) while the other had low availability (3 kg per 100 pounds). The scientists used automatic behavior recorders attached to the cows to track how much time they spent grazing and chewing their food throughout the day. They also directly observed the cows for 30 minutes each day to count how many feeding stations (different spots where cows stopped to eat) they visited per minute and how many bites they took at each spot. Researchers measured the amount and nutritional quality of available grass and tracked exactly how much each cow ate daily.
This research approach is important because it combines automatic technology with direct observation to capture the complete picture of how cows behave when eating. Simply measuring how much cows eat is not enough. Understanding the detailed behaviors like how selective they are and how they adjust their grazing patterns helps farmers make better decisions about pasture management. The two-year study period strengthens the findings by showing that results were consistent across different seasons and conditions.
The study used objective measurement tools (automatic recorders) combined with direct observation, which increases reliability. The researchers studied the same cows over two years, allowing them to see if patterns repeated. However, the study was conducted in one specific climate and grass type, so results may not apply everywhere. The statistical significance of some findings was marginal (close to but not quite reaching standard thresholds), suggesting some results should be interpreted cautiously.
What the Results Show
Cows with high grass availability ate substantially more food than cows with limited grass. In the first year, high-availability cows ate 1.3 kilograms more per day, and in the second year this increased to 3.7 kilograms more per day. This greater food intake was possible because these cows had access to more total grass in the pasture. Beyond just eating more, the cows with abundant grass changed their eating strategy. They visited more feeding stations per minute (the spots where they stopped to eat) and took smaller bites at each station, suggesting they were being more selective about which plants and plant parts they chose. This selective behavior makes sense: when grass is plentiful, cows can afford to be picky and choose the most nutritious parts. The cows with limited grass, by contrast, had to eat whatever was available without being selective.
In the second year, cows with limited grass showed an interesting adaptation: they spent more time chewing their food relative to how much they ate. This suggests that when cows cannot eat enough fresh grass, they compensate by chewing longer to break down food into smaller pieces. Longer chewing helps extract more nutrients from lower-quality forage and makes room in the stomach for more food. This behavioral shift shows that cows actively adjust their eating strategies when faced with limited resources, attempting to maximize nutrition from whatever grass is available.
This study builds on existing knowledge that grass availability affects cow nutrition and milk production. Previous research has shown that more grass generally means more food intake, but this study provides detailed behavioral explanations for why this happens. The finding that cows become more selective when grass is abundant aligns with ecological theory about foraging behavior in animals. The adaptation of increased chewing time when grass is scarce has been observed in other ruminant species, so this research confirms similar patterns in beef cattle.
The study was conducted in subtropical grasslands with specific native grass species, so results may not apply to other climates or pasture types. The sample size of 34 cows is moderate, which means some findings had only marginal statistical significance. The study focused on a specific time period (40 days after calving), so it is unclear if these patterns continue throughout the entire lactation cycle. The research did not measure actual milk production or quality, only the eating behaviors and food intake that support milk production. Additionally, the study did not account for individual cow differences in genetics or prior experience that might affect foraging behavior.
The Bottom Line
Farmers should prioritize maintaining adequate grass availability during the critical lactation period after cows give birth, as this directly increases food intake and supports milk production. Aim for at least 5 kilograms of dry matter grass per 100 pounds of cow body weight daily. This recommendation has moderate to strong evidence from this two-year study, though farmers should adapt it to their specific climate and grass types. Monitoring pasture conditions and adjusting stocking rates accordingly is a practical management strategy.
Beef cattle farmers and ranchers managing lactating cows should apply these findings, particularly those in subtropical or warm-climate regions with native grasslands. Dairy farmers may find some relevance, though dairy cattle are often managed differently. Farmers in temperate climates with different grass species should interpret results cautiously and may need to conduct similar studies in their own regions. Agricultural extension agents and pasture management consultants should consider these findings when advising clients.
Farmers should expect to see changes in cow eating behavior within days of adjusting grass availability. Improvements in milk production and cow body condition typically become apparent within 2 to 4 weeks of maintaining adequate grass availability. The full benefits for herd health and reproduction may take several months to become evident.
Frequently Asked Questions
How much grass do nursing cows need to eat enough?
Research shows nursing cows need at least 5 kilograms of dry matter grass per 100 pounds of body weight daily to maximize food intake and milk production. Cows with this amount of grass availability ate 1.3 to 3.7 kilograms more per day than those with limited grass.
Do cows eat differently when there is more grass available?
Yes, cows become more selective eaters when grass is abundant. They visit more feeding spots per minute and take smaller bites, allowing them to choose higher-quality plants and plant parts rather than eating whatever is available.
What happens to cows when there is not enough grass?
When grass is limited, cows spend more time chewing their food to break it down into smaller pieces and extract more nutrients. This behavioral adaptation helps them maximize nutrition from lower-quality forage but cannot fully compensate for limited food availability.
When is grass availability most important for beef cows?
Grass availability is critical during the first 40 days after cows give birth, when they are nursing calves and need extra nutrition for milk production. This is the most demanding period for lactating cows and when pasture management has the biggest impact.
Can farmers use this research to improve milk production?
Yes, farmers can increase milk production by maintaining adequate grass availability during lactation. Ensuring cows have sufficient pasture to graze selectively supports higher food intake and better nutrition, which directly supports milk production for nursing calves.
Want to Apply This Research?
- Track daily pasture grass mass (measured in kilograms of dry matter per acre) and correlate it with milk production records or estimated milk output based on calf weight gain. Record observations of cow grazing behavior such as time spent grazing and apparent selectivity.
- Users can implement a pasture rotation system that maintains minimum grass availability thresholds. Set reminders to assess pasture conditions weekly and adjust herd movement or supplemental feeding based on available forage. Log observations about cow grazing behavior and milk production to identify optimal grass availability levels for their specific operation.
- Establish a baseline measurement of current grass availability and cow performance. Monitor pasture mass weekly during the lactation season using simple measurement tools. Track milk production or calf growth as an indicator of nutritional adequacy. Adjust management practices based on seasonal variations and maintain records to identify patterns across years.
This research describes grazing behavior and food intake in beef cattle under specific subtropical grassland conditions. Results may not apply to all cattle breeds, climates, or grass types. Farmers should consult with local agricultural extension agents or veterinarians before making significant changes to pasture management or feeding practices. This study measured eating behavior and food intake but did not directly measure milk production or calf health outcomes. Individual cow genetics, health status, and prior experience can affect grazing behavior and should be considered in management decisions.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.