Dietary Neutral Detergent Fiber Levels Impacting Dairy Cows’ Feeding Behavior, Rumen Fermentation, and Production Performance during the Period of Peak-Lactation

SIMPLE SUMMARY: Dietary neutral detergent fiber (NDF) is commonly used as an indicator of the fiber content in animal diets, particularly in ruminant nutrition. NDF plays a crucial role in the digestive process of ruminant animals, as it affects feed intake, rumen fermentation, and nutrient utilization. The levels of NDF affect feeding behavior, rumen fermentation, and production performance during the period of peak lactation in dairy cows. To prove it, four Holstein dairy cows were subjected to a feeding experiment with varying NDF levels in their diets. The results indicated that increased NDF levels resulted in reduced dry matter intake, while the time spent eating and ruminating increased. Moreover, higher NDF levels led to increased pH value and acetate concentration, as well as changes in the proportions of certain bacteria in the rumen. Milk yield, protein percentage, and nitrogen efficiency decreased with increasing NDF levels, while milk fat percentage and milk urea nitrogen concentration increased. Notably, diets with 25% and 34% NDF had negative effects on feeding behavior, rumen fermentation, and production performance. However, the diet with 28% NDF was effective in enhancing the production performance compared to the one with 31% NDF. These findings offer a valuable strategy for optimizing the provision of dietary NDF to cattle, thereby enhancing their overall performance. ABSTRACT: This study investigated the impact of dietary neutral detergent fiber (NDF) levels (25.49%, 28.65%, 31.66%, and 34.65%, respectively) on the feeding behavior, rumen fermentation, cellulolytic bacteria, and production performance of dairy cows during peak lactation. A feeding experiment was conducted using four fistulated Holstein dairy cows (600 ± 25 kg) with days in milk (50 ± 15 days), employing a 4 × 4 Latin square design to assign the cows to four groups. The results demonstrated that increasing NDF levels in the diet had the following effects: (1) A linear decrease in dry matter intake (DMI), NDF intake, and physically effective NDF(8.0) (peNDF(8.0)) intake; a linear increase in the average time spent eating and ruminating, as well as the time spent eating and ruminating per kilogram of dry matter (DM); a quadratic response in the time spent ruminating per kilogram of NDF and peNDF(8.0). (2) A linear increase in average pH value, acetate concentration, and the proportions of Fibrobacter succinogenes and Ruminococcus flavefaciens among total bacteria; a linear decrease in ammonia nitrogen (NH(3)-N) concentration, microbial crude protein (MCP), total volatile fatty acid (TVFA), propionate, butyrate, and lactate. (3) A linear decrease in milk yield, milk protein percentage, and nitrogen efficiency of dairy cows; a linear increase in milk fat percentage and milk urea nitrogen (MUN) concentration. Based on the combined results, it was found that diets with 25% and 34% NDF had detrimental effects on the feeding behavior, rumen fermentation, and production performance of dairy cows. However, the diet with 28% NDF showed superior outcomes in production performance compared to the one with 31% NDF. Therefore, it is strongly recommended to include a diet containing 28% NDF during the critical peak lactation period for dairy cows.