# Effect of Corn Processing and Protein Degradability on Ruminal Metabolism and Feeding Behavior of Dairy Cows

## TL;DR

This study shows how processing corn and adjusting protein degradability can improve digestion and feeding behavior in dairy cows, leading to better milk production and nitrogen use.

## Contribution

The study reveals how steam-flaked corn and protein degradability interact to influence ruminal metabolism and feeding behavior in dairy cows.

## Key findings

- Steam-flaked corn increases propionate and reduces acetate/propionate ratio in the rumen.
- Highly degradable protein combined with ground corn increases ruminal ammonia and branched-chain fatty acids.
- Steam-flaking reduces feed selectivity and improves nitrogen retention and utilization efficiency.

## Abstract

In Brazil, the main corn used for dairy cows feeding has a highly vitreous endosperm, which can reduce digestibility because starch granules are embedded in a dense protein matrix. Processing techniques such as grinding or flaking can improve ruminal starch availability and energy use. In this study, we evaluated how corn processing and protein degradability influence ruminal fermentation and feeding behavior in lactation Holstein cows. In general, steam-flaked corn increased concentrations of propionate and reduce acetate/propionate ratio in rumen. Our findings demonstrate that both corn processing and protein degradability affect nutrient utilization and feed selection, emphasizing the importance corn processing optimization and protein degradability to improve milk production efficiency and nitrogen use in dairy herds.

This study investigated how corn processing and protein degradability affect ruminal fermentation and feeding behavior in lactating Holstein cows. Twenty cows (averaging 162 ± 70 days in lactation, 666 ± 7 kg body weight, and 36.0 ± 7.8 kg/day milk yield) were assigned in a Latin square design with four 21-day periods and four treatments arranged in a 2 × 2 factorial: corn processing [ground corn (GC) vs. steam-flaked corn (SFC)] and crude protein (CP) degradability [high (HCP) vs. low (LCP)]. Ruminal samples were collected at eight time points (0, 2, 4, 6, 8, 10, 12 and 16 h) post-feeding to analyze pH, ammonia, and short-chain fatty acids, while feeding behavior was recorded visually every 5 min for 48 h. Corn processing and protein degradability interacted to influence rumen ammonia nitrogen (p = 0.057), urinary pH, (p = 0.041), nitrogen secretion and efficiency (p = 0.538), and feeding (min/kg DM; p = 0.049) and rumination times (min/kg DM, p = 0.001; min/kg NDF, p = 0.001), reflecting changes in nitrogen metabolism. Steam-flaked corn decreased the acetate/propionate ratio and enhanced propionate production, improving nitrogen retention and reducing urinary N losses, while highly degradable protein increased ruminal NH3-N and branched-chain VFA concentrations, particularly when combined with ground corn. Additionally, steam flaking reduced feed selectivity and increased rumination efficiency, supporting more effective use of nutrients for milk N secretion and overall nitrogen utilization efficiency in dairy cows. Overall, diets varying in corn processing and protein degradability altered ruminal metabolism, nutrient utilization, feeding behavior, and diet selectivity in lactating cows, highlighting their importance in optimizing dairy cow performance.