Effect of replacing corn grain flake with sorghum grain ground fine as the main energy source in lactating cows diet, on productive performance and health status.

The purpose of this experiment was to compare flaked corn and sorghum meal on lactating cows performance and health status. Steam-flaked corn has a rate of ruminal starch degradability of 25%/hour compared to a 7 %/hour for sorghum meal, with an intestinal digestibility of 90% and 75%, respectively. Diets were formulated using 38% grass hay, 4% straw, 21% protein and mineral supplement and 38% of either corn flakes (C diet) or sorghum meal (S diet). Eight lactating Holstein dairy cows, averaging 204 days in milk and producing 31 kg milk/day were divided in two homogenous groups and fed the two experimental diets in a cross over design with a 8 days adaptation and 5 days collection (13 days for each period). Dry matter and water intake, milk production and quality, and rumination time were recorded daily. Ruminal pH was measured continuously at 10 min intervals. Fecal samples were collected twice daily (at 8 am and 8 pm) for pH and dry matter content. Ruminal fluid and blood samples were collected at the end of every period. Data were analyzed with GLM – ANOVA for repeated measures using the software Statistica v.10. Dry matter intake was not different between treatments whereas water intake was higher in S compared with C diet (155 vs. 138 liters/day; P≤0.05). Milk production did not differed between treatments, whereas milk fat was higher for S diet (3.78% vs. 3.54% for S and C diet, respectively; P≤0.05). Milk urea was lower in C diet compared with S (P≤0.05). No difference was found for rumination time and ruminal pH. VFA profile showed higher content of acetic (P≤0.05), isobutiric (P≤0.01) and isovaleric acids (P≤0.01) for S diet, while propionic acid was higher in C diet (P≤0.01). In C diet the C2 to C3 ratio was 2.2 compared to 3.5 in S diet (P≤0.01). No differences were found in fecal pH and dry matter. Blood parameters showed a lower plasma urea (P≤0.01) and phosphorus (P≤0.05) content for C diet. In conclusion, replacing flaked corn with the same amount of sorghum meal did not affect productive performance although a better fat content in milk was achieved, as sustained by an higher ruminal acetic acid production. On the other side, the flaked corn-based diet improved nitrogen utilization, due to highly digestible carbohydrate available for ruminal fermentation, resulting in a decreased urea content both in the rumen and in the blood.