Effects of functional oils on ruminal fermentation, rectal temperature, and performance of dairy cows under high temperature humidity index environment

The hypothesis of the current study was that functional oils (FO) could replace monensin (MON) in diets while improving thermal status and performance of dairy cows. This study was designed to evaluate the effects of a blend of FO and MON on nutrient intake and total tract digestion, ruminal fermentation, glucose and urea concentrations in blood, heart rate, rectal temperature, and milk yield and composition of dairy cows under heat stress in Brazil. Thirty-six Holstein cows [201 63 days in milk, 599 78 kg of body weight, and 28.7 +/- 3.92 kg/d of milk yield (mean +/- SD)] were used in a randomized complete block design experiment that lasted six weeks (one week for covariate adjustments and five weeks for treatment effect evaluation). Cows within blocks were assigned individually to one of the following treatments: 1) control (CON), basal diet without feed additives; 2) functional oils (FO), basal diet added 500 mg/kg DM of a commercial blend of cashew nut shell liquid and castor oil; and 3) monensin (MON), basal diet added 22 mg/kg DM of sodium monensin. Additives were provided mixed into the concentrate and total mixed ration (TMR) was fed twice daily. The experimental barn daily temperature, air relativity humidity, and temperature humidity index were 25.0 +/- 0.25 degrees C, 81.7 +/- 1.17%, and 74.6 +/- 0.28, respectively (mean SE), suggesting that heat stress likely impacted cows. Cows fed MON had lower (P = 0.012) dry matter intake despite treatments have not affected total tract digestibility of nutrients and ruminal fermentation (pH, NH3-N, and VFA concentration). Both MON and FO increased (P = 0.006) serum urea concentration without affecting serum glucose levels. Treatments had no effect on heart rate, respiration rate, and rectal temperature. Although treatments did not affect milk yield and fat-corrected milk, cows fed FO had a greater (P = 0.021) milk fat content than those fed MON. Cows fed FO exhibited the highest value of milk fat content (34.6, 32.5, and 36.5 g/kg for CON, MON, and FO, respectively). This study did not show evidence that treatments can decrease body temperature, but FO may replace MON in diets to maintain milk fat concentration without affecting dry matter intake and milk yield of cows under heat stress.