Summary
This study examined how substituting corn products (starch) for citrus pulp (neutral detergent-soluble fibre) as sources of soluble carbohydrates in dairy cattle diets affected production and rumen physiology. Across two trials (11 individually-fed cows in Experiment 1; 184 group-fed cows in Experiment 2), corn-based diets increased milk yield, corrected milk yield, and milk protein output, whilst citrus pulp diets increased milk fat concentration and milk urea nitrogen. Ruminal fermentation patterns differed between diets, though organic acid concentrations were similar, suggesting that carbohydrate source composition influences both production efficiency and nitrogen metabolism in lactating cattle.
Regional applicability
The findings are relevant to United Kingdom dairy farming, as both citrus pulp and corn products are common feed ingredients in UK dairy rations. The study's use of forage-based diets (corn silage and alfalfa hay) and Holstein cattle is representative of commercial dairy systems in temperate regions including the UK, though locally-available forage species and supplementary feed options may vary.
Key measures
Milk yield (kg/d), milk fat percentage and yield (kg/d), milk protein percentage and yield (kg/d), fat- and protein-corrected milk (kg/d), milk urea nitrogen (mg/dL), ruminal pH, ruminal H+ concentrations, ruminal organic acid concentrations
Outcomes reported
The study measured milk yield, milk composition (fat, protein, urea nitrogen), and rumen fermentation parameters (pH, organic acid concentrations) in dairy cows fed diets differing in sources of neutral detergent-soluble carbohydrates. Two reversal experiments compared citrus pulp-based diets (supplying neutral detergent-soluble fibre) against corn product-based diets (supplying starch).
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