Effects of plant extracts on milk yield and apparent efficiency of lactating dairy cows during hot weather 1

A study was conducted to evaluate the effects of plant extracts on milk yield, apparent efficiency of yield, and nutrient digestibility in hot weather. The plant extracts were composed of proprietary blends of selected fermentation metabolites CitriStim yeast, Aspergillus niger, and plant extracts capsicum, cinnamaldehyde, and eugenol, which were selected for the potential ability to improve physiological response to heat stress. Thirty-six Holstein cows averaging 187 ± 16 DIM and 44.1 ± 0.5 kg/d of milk were used in a 10-wk randomized complete-block design from June through August 2007. Cows were fed a control diet during a 2-wk standardization period. Cows were blocked into groups of 3 based on DIM, DMI, and milk yield, and randomly assigned within block to 1 of 3 treatments for 8 wk. Treatments were control (C), ThermalCare D (TD), and ThermalCare R (TR). Diets were cornsilage-based and balanced to be isocaloric and isonitrogenous. No differences in DMI, milk yield, or energy-corrected milk were observed among treatments. Milk fat percentage was reduced (P = 0.003) for TD and TR versus C and milk fat yield (kg/d) was reduced (P = 0.05) for TD versus TR (1.49) and C. Efficiency (defined as energy-corrected milk/DMI) was reduced (P = 0.03) for TD compared with C. No differences were observed in body temperature, respiration rate, or concentrations of serum glucose and urea N among treatment. Intake of DM (P = 0.05) and ADF (P = 0.01) was increased for TR, and digestibility of ADF was increased for TD and TR compared with C during wk 5. Results suggest that feeding supplemental plant extracts did not affect milk yield, but did affect milk components and improved ADF digestibility.