Liat Schiowitz, Graduate Student and Dr. Grazyne Tresoldi, Assistant Professor, Department of Animal Sciences, The Ohio State University
In this final article of our four-part series, we bring together the core components of early-life nutrition that boosts calf welfare and lifetime performance. Having covered colostrum, milk, and fresh water, today we focus on establishing the digestive capacity required for a successful transition at weaning and beyond: the solid diet.
Building the Functional Rumen: Grain and Forage
You probably are familiar with the idea that the calf grain starter – or more specifically the volatile fatty acids (VFA) produced by its fermentation – stimulates papillae growth, so that the rumen can become functional and absorb nutrients into the bloodstream. Beyond chemical development, it may also provide enough particle structure to trigger chewing and rumination.
However, another often-overlooked, essential component of the solid diet is forage. While some starters get chewing started, forage provides the additional physical bulk and muscular stimulation needed for the rumen to expand in volume and develop optimal motility. Physical fiber also keeps the rumen wall healthy by reducing buildup on the lining. It sustains long-term rumination and saliva flow, keeping ruminal pH optimal.
In addition, both grain and forage provide the essential nutrients necessary to cultivate a diverse population of microbes throughout the rumen and gut. As fermentation activity increases, these microbes establish a stable, mature ecosystem. Research has shown that early colonization and the establishment of a healthy microbiome influence metabolic efficiency and immune system development, yielding persistent, positive benefits into adulthood.
What Makes a High-Quality Solid Diet?
Establishing early solid feed intake requires balancing multiple aspects such as palatability, physical texture, particle size, nutritional density, and overall quality. Calves are quick to sort through feed and will pick out components they dislike or reduce feed intake altogether.
Starter Grain
Texture and physical form: coarsely texturized starter (containing whole, cracked, or steam-flaked grains blended with molasses) often supports healthier ruminal pH and can improve intake compared to finely ground or pelleted feeds. Coarse grains increase chewing time, encourage earlier rumination, and boost natural saliva buffering. Calves dislike fine, dust-like particles and will refuse to eat them, reducing dry matter intake (DMI) by ~10%.
Nutritional specifications: Target 20 to 22% crude protein (DM basis), focusing on the availability of essential amino acids (lysine, methionine, and threonine) to support lean frame growth under higher milk feeding programs. Texturized starters can safely contain 35 to 40% starch due to their larger particle size, whereas high starch in finely ground or pelleted feeds ferments too quickly. Keep supplemental fat under 5% as high fat diets reduce intake and fiber digestion.
Forage
Although some may believe forage causes "potbellies" or stalls growth, research in this area has grown rapidly and shown that when fed at precise levels, forage complements starter intake, often increasing total intake and body weight. Common forage choices include hay (e.g., alfalfa, oat, and grass hays), silage (e.g., corn, triticale), straw (e.g., wheat, barley), and pasture.
As a general starting point, aim for roughly 12% of total DM as forage, but optimal inclusion depends on forage type and quality. Highly digestible forages like alfalfa or good oat/grass hay can be fed at higher rates without displacing energy-dense starter intake. For example, alfalfa can be fed up to 20% for optimal performance, whereas low-quality forages like straw are included at low rates (~9%) not for growth but to support ruminal pH and rumen health.
Particle size matters: Forage should be coarsely chopped to 1 to 2 inches to reduce feed sorting, stimulate rumination, and maintain a clean, healthy rumen lining. Additionally, providing forage reduces non-nutritive oral behaviors, such as cross-sucking or licking pen fixtures.
How to Offer Solid Feeds
Even the highest quality starter and forage won't yield good results if management doesn't match calf feeding behavior. Key considerations include:
- Offer starter and forage separately: providing feeds in separate containers allows calves to self-regulate their fiber intake without reducing grain consumption.
- Introduce solid feed early: offer small amounts early to entice calves to explore and consume solids. Calves often sample feed as early as day 3 of life. If providing forage later, research shows introducing it by week 2 yields better growth performance and rumen development compared to waiting until week 4 or 6.
- Keep feed fresh: replace starter daily, starting with small handfuls and increasing as intake grows. Always pair solid feed with continuous access to clean, fresh water, which creates the fluid environment required for rumen fermentation to take place.
- Container design matters: calves seem to prefer eating from shallow containers compared to placing their heads deep into buckets, where their eyes are covered and vision is obstructed.
- Harness social facilitation: calves housed in pairs or small groups often begin eating earlier and in larger quantities than individually housed calves, as bolder pen-mates teach timid calves through social learning. Always adjust feeding practices to account for competition (such as providing multiple feeding containers).
Setting up Calves for a Successful Weaning
While calves are traditionally weaned based on age, solid feed intake is the most reliable metric for weaning readiness. To ensure a smooth transition, calves should be consuming at least 2.5 to 3 lb/day of starter for 3 consecutive days before milk is completely removed. Because solid intake varies with milk allowance, calves fed higher milk volumes may reach this benchmark later. However, there are substantial long-term benefits to this trade-off, as discussed in Part 2.
Reduce milk gradually. Abrupt milk removal often results in a "slump" where calves lose weight or stagnate because they haven't learned to consume enough solid feed to meet their energy needs. A 7- to 14-day gradual milk step-down (reducing volume, frequency, or diluting milk) creates a gentle energy deficit that prompts the calf to increase solid feed intake, boosting ruminal maturation and reducing signs of distress.
Take-Home Messages (Table 1)
- Solid diet encompasses both grain starter and forage. Each play distinct, complementary roles in establishing chemical absorption, physical strength, and microbial diversity in the digestive tract.
- When fed at recommended levels, high quality forages increase total dry matter intake and body weight gain.
- Watch your calves: along with their growth, measure what and how much they are eating to guide management decisions.
- Feeding goes beyond what is fed: management aspects such as container design, feed freshness, and social companionship directly affect how much solid feed calves consume.
- All aspects of early-life nutrition are intertwined: milk allowance, starter specifications, forage quality, and water access work as an integrated system. Work closely with your nutritionist and Extension team to align solid diet parameters with your specific milk program and farm goals.
Table 1. Key benchmarks: Solid diet and weaning transition.
| Management Area | Target/Benchmark | Why it Matters |
| Solid diet introduction | As early as possible, in shallow containers. | Stimulates early exploration and solid feed intake; calves prefer to eat from shallow containers. |
| Starter type and formulation | Coarsely texturized; 20 to 22% CP, 35 to 40% starch, <5% fat. | Supports rumen lining development and lean frame growth under high milk allowances. |
| Forage inclusion and delivery | 12% of DM, coarsely chopped, fed in a separate container. | Stimulates rumen volume expansion and muscular motility without compromising starter intake; allows self-regulation of fiber. |
| Weaning readiness | Calves eat 2.5 to 3 lb/day of starter for > 3 days. | Ensures the rumen microbial population and surface area can fully support growth post-milk. |
| Weaning method | 7 to 14-day gradual milk step-down | Prevents post-weaning growth slumps and minimizes weaning distress. |
Selected References
Castells, Ll., A. Bach, G. Araujo, C. Montoro, and M.Terré. 2012. Effect of different forage sources on performance and feeding behavior of Holstein calves. J. Dairy Sci. 95(1), 286–293. https://doi.org/10.3168/jds.2011-4405
Ghaffari, M.H., J.K. Drackley, and A.F. Kertz. 2025. Invited review: Unlocking growth and development potential in dairy calves through precision protein feeding. J. Dairy Sci.108, 6601–6616. https://doi.org/10.3168/jds.2025-26419
Miller-Cushon, E.K., and T.J. DeVries. 2015. Invited review: Development and expression of dairy calf feeding behaviour. Can. J. Anim. Sci. 95(3), 341–350. https://doi.org/10.4141/cjas-2014-163
Song, Y., S. Wen, and L.L. Guan. 2026. Unraveling the dynamic changes in the intestinal microbiome: Impacts on pre-weaning calf health and productivity. J. Anim. Sci. Biotechnol. 17(1). https://doi.org/10.1186/s40104-026-01354-6
Toledo, A.F., A.P. Silva, F.V. Barbosa, R.D. Barboza, I.C. Oliveira, E.D. Marino, D.M. Polizel, and C.M. Bittar. 2024. Forage sources in total mixed rations on rumen fermentation, gut fill, and development of the gastrointestinal tract of dairy calves. Sci. Rep. 14(1). https://doi.org/10.1038/s41598-024-80271-y
Xiao, J., G.M. Alugongo, J. Li, Y. Wang, S. Li, and Z. Cao. 2020. Review: How forage feeding early in life influences the growth rate, ruminal environment, and the establishment of feeding behavior in pre-weaned calves. Animals 10, 188. https://doi.org/10.3390/ani10020188
Xiao, J., J. Tian, Y. Peng, R. Hu, Q. Peng, L Wang, B. Xue, and Z. Wang. 2025. Effects of forage feeding to calves on performance, rumen fermentation, and nutrient digestibility: A meta-analysis. J. Dairy Sci. 108(1), 430–447. https://doi.org/10.3168/jds.2024-24917