A recently published study in the Journal of Dairy Science examined a practical question many calf managers have asked: does adding water to a calf TMR improve intake and performance? Conducted on a commercial dairy farm in Hemmat (Tehran, Iran), the research compared two TMR moisture levels and two forage sources to evaluate effects on feed sorting, digestibility, rumen fermentation, and growth through weaning and into the post-weaning period.
What the study did
The team followed 48 Holstein calves from day 3 to day 80, with weaning completed at day 65.
Researchers used a 2 × 2 factorial design, testing:
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TMR moisture level: 10% vs. 50%
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Forage source: alfalfa hay (AH) vs. wheat straw (WS)
This created four treatment groups:
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WS10, WS50, AH10, and AH50
All diets were formulated to contain similar crude protein levels (approximately 20% CP) and included about 7.5% forage on a dry matter basis.
The headline result
Moisture improved intake most when alfalfa hay was the forage source.
Calves fed AH50 (alfalfa hay with 50% moisture) showed:
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The highest overall dry matter intake (DMI)
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The highest TMR intake
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Greater metabolizable energy intake
In contrast, adding moisture to the wheat straw–based ration did not produce the same intake response. The most consistent benefits appeared when alfalfa hay and higher moisture were used together.
Growth performance: where gains appeared
Average daily gain (ADG) across the entire study did not differ significantly among treatments. However, differences emerged after weaning:
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Calves fed the 50% moisture TMR had higher post-weaning ADG than those fed the drier ration.
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Calves receiving alfalfa hay gained more post-weaning than those fed wheat straw.
Final body weight and feed efficiency were not significantly affected by treatment.
Digestibility: wetter diets improved nutrient use
Adding moisture to the TMR increased:
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Dry matter digestibility
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Organic matter digestibility
Forage source also played a role. Calves fed alfalfa hay had higher dry matter and NDF digestibility than those fed wheat straw, regardless of moisture level.
Rumen fermentation: modest but consistent shifts
Rumen pH was not affected by diet. However, calves fed the higher-moisture TMR showed:
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Increased ruminal ammonia-N
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Higher total volatile fatty acid (VFA) concentrations
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A higher molar proportion of acetate during the post-weaning period, or a tendency toward higher acetate overall
These changes suggest more active rumen fermentation, particularly as calves transitioned to greater solid feed intake.
Sorting behavior: moisture changed refusals
Feed sorting occurred across most treatments, with refusals differing in particle size from the original diet.
Calves fed AH50 showed less disruptive sorting behavior compared with other groups. A wetter, alfalfa-based TMR appeared harder for calves to selectively sort, resulting in a more uniform intake.
What this means for calf programs
The results point to a practical takeaway:
When alfalfa hay is included, increasing TMR moisture may help calves consume more feed and transition more smoothly through weaning.
With wheat straw, intake and performance responses to added moisture were less pronounced, likely due to straw’s physical characteristics and lower fermentability.
Practical considerations
Before adding water to calf rations, managers should consider:
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Thorough mixing to limit ingredient separation
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Feeding fresh rations daily
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Monitoring refusals closely
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Managing hygiene carefully, especially in warm conditions, to avoid heating or spoilage
Bottom line
Adding moisture to calf TMR is not a universal solution. In this study, the clearest benefits occurred when alfalfa hay was paired with higher moisture, supporting intake, digestibility, rumen fermentation, and post-weaning growth. The findings reinforce the importance of considering both forage source and physical characteristics of the diet when adjusting calf feeding strategies.
