Álvaro García
Calf programs are often evaluated using the metrics that are easiest to measure. Weaning weight, disease incidence, treatment costs, and feeding expenses typically dominate the discussion. These indicators are important, but they do not fully capture what is at stake. A growing body of research continues to show that performance during the first weeks of life influences biological efficiency, reproductive development, and first-lactation milk yield.
Early growth differences emerge quickly
A recent long-term study from the University of Bonn, Germany, published in 2026 in the Journal of Dairy Science, followed Holstein heifers from birth through first lactation under an intensified milk feeding program. Calves received up to 12 L of milk replacer per day (approximately 3.2 gal), followed by a gradual weaning period extending to week fourteen. Despite uniform management, calves exhibited distinct growth trajectories during the first two months of life.
One group achieved an average daily gain of approximately 1.06 kg per day (2.34 lb. per day), while the second group averaged 0.84 kg per day (1.85 lb. per day).
Importantly, these differences were not explained by birth weight or colostrum quality. Birth weights were identical at approximately 41 kg (90 lb.), and colostrum intake and quality were also comparable. The divergence instead reflected voluntary nutrient intake and feed efficiency, particularly during the first two weeks of life.
Calves with higher early gains consumed more milk replacer, visited feeders more frequently, and converted feed energy into body weight more efficiently.
Early advantages persisted through rearing
At weaning, higher-growth calves were approximately 16 kg heavier (35 lb.). This difference persisted throughout rearing. These heifers reached the 400 kg breeding threshold (882 lb.) an average of 42 days earlier than their counterparts.
Earlier physiological maturity without additional postweaning nutritional intervention represents a meaningful efficiency gain within replacement programs. However, the most economically relevant outcome appeared during first lactation. Heifers with higher preweaning gains produced approximately 3.8 L more milk per day (about 8.4 lb.). Over a standard 305-day lactation, this translated into 1,269 kg of additional milk (2,798 lb.).
This magnitude of response is consistent with earlier foundational work demonstrating that preweaning average daily gain is strongly associated with future milk production. Biological programming effects are increasingly recognized as a vital component of lifetime productivity.
The study also observed differences in milk urea nitrogen (MUN). Heifers with stronger early growth exhibited lower MUN concentrations, suggesting improved nitrogen utilization efficiency. Because both groups received identical diets later in life, this difference reflects underlying metabolic efficiency rather than ration composition.
Feeding behavior as a driver of early growth
Recent research has highlighted that growth divergence is not solely a function of diet formulation. Feeding behavior plays a vital role. In the study by Hemmert et al. (2026), calves exhibiting higher early growth rates displayed distinct behavioral patterns at automated feeders. These animals visited milk stations more frequently, consumed a greater proportion of their entitlements, and demonstrated fewer incomplete meals.
Behavioral variables proved highly predictive of growth classification. Measures such as visit frequency, meal consistency, and the ratio of visits to milk versus concentrate feeders were associated with average daily gain.
These findings reinforce a key biological principle. Growth differences often emerge from variation in voluntary intake dynamics rather than nutrient supply alone.
From a management perspective, feeding behavior metrics provide actionable information. Calves with low engagement, incomplete meals, or inconsistent intake patterns warrant closer evaluation. These behaviors frequently reflect underlying constraints such as health challenges, social competition, or environmental stressors.
For producers using automated feeding systems, behavioral data can function as an early management signal. Deviations in feeding consistency often precede measurable differences in body weight.
Exogenous enzymes and early-life efficiency
While intake dynamics explain much of the observed growth variation, nutrient utilization remains central to biological efficiency. A recent systematic review published in the Journal of Dairy Research examined the effects of exogenous enzymes (EE) in dairy calves and provides useful context for understanding how early nutritional interventions may influence performance.
Through seventeen controlled studies, enzyme supplementation consistently improved fiber digestibility. This finding is biologically logical. Fiber-degrading enzymes enhance the breakdown of structural carbohydrates, potentially increasing the availability of fermentable substrates during a period when the rumen microbial ecosystem is still developing.
However, improvements in digestibility did not always translate into higher average daily gain. Growth responses were variable across experiments. Enhanced digestion does not guarantee increased growth when other constraints such as intake, health status, or environmental stress limit performance.
Importantly, several studies reported behavioral benefits. Calves receiving enzyme supplementation often displayed reduced non-nutritive oral behaviors, increased resting time, and greater rumination activity. These responses suggest that digestive comfort and rumen function may improve even when body weight differences are modest.
As with many nutritional technologies, enzyme responses are influenced by diet composition, enzyme type, dose rate, and management conditions. Their value should therefore be evaluated within the broader framework of system efficiency rather than short-term growth alone.
Practical implications for producers
First, the first two weeks of life remain a critical biological window. Differences in intake and efficiency during this period strongly influence later outcomes.
Second, growth variation exists even under consistent feeding programs. Monitoring intake behavior and weight gain is therefore essential.
Third, early growth advantages translate into measurable economic returns through earlier breeding readiness and increased milk yield.
Finally, feeding behavior metrics provide valuable decision-support information. Calves with low engagement, incomplete meals, or inconsistent intake patterns warrant closer evaluation for health, competition, or environmental stressors.
Early growth is not merely about achieving acceptable weaning weights. It is about shaping a future cow capable of higher biological efficiency and improved production performance.
The full list of references used in this article is available upon request.
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