Dietary protein level and corn processing method: Lactation performance, milk fatty acid composition, rumen and blood parameters of lactation dairy cows

The objective of this experiment was to evaluate the interactive effects of corn processing and dietary protein level on milk production and composition, as well as rumen and plasma metabolites in lactation dairy cows. Eight multiparous mid lactating Holstein cows, averaging 105 ± 9 d in milk and producing 47.2 ± 3 kg milk/d were randomly assigned in a replicated 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments. Experimental diets contained either finely ground corn (FGC) or steam flaked corn (SFC) each with either low protein (LP, 14.8%) or high protein (HP, 16.2%) content. Data were analyzed using PROC MIXED of SAS with significance declared at P ≤ 0.05. Cows fed HP diets had greater milk production and lower milk fat percentage than those for cows fed LP diets. Cows on LP diets however had greater medium-chain fatty acid (FA) and saturated FA but lower monounsaturated FA, polyunsaturated FA and unsaturated FA compared with cows on HP diets. Reduction of milk fat for cows on HP was associated with lower amount of short and medium chain FA and higher unsaturated FA content in milk fat. Blood glucose (74.7 vs 69.3 mg/dL) and cholesterol (275.2 vs 262.9 mg/dL) were greater for cows fed SFC than cows fed FGC. Corn processing had no detectable effect on milk production; however, cows on FGC had greater milk fat percentage and production and lower milk: feed ratio than cows fed SFC. Cows fed SFC had greater amount of short chain FA and polyunsaturated FA and lower C16:0 (30.5 vs 29.3) and C18:0 (9.1 vs 8.2) in milk fat than cows fed FGC. Treatments had no effect on ruminal VFA concentration and pH. Milk and blood urea, and rumen nitrogen (N) were lower for cows when fed SFC or LP diets. Cows fed SFC or LP had greater N efficiency than cows fed FGC or HP diets. These findings showed that cows supplemented with SFC or fed LP diets had a more efficient use of dietary N. Results indicate that employing a 14.8% CP diet is insufficient for maximum milk production even with corn flaking. Cows fed LP diets had similar milk: feed ratio and greater N efficiency. Compared with FGC diets, SFC diets improved feed and N efficiency while reducing N loss and increasing the glucose concentration.