Intake, milk production and heat stress of dairy cows fed a citrus extract during summer heat

This study determined effects of feeding a citrus extract (CE) to high producing dairy cows during summer heat on measures of heat stress, as well as milk production and composition, in a replicated 2 x 2 Latin square experiment with two 28 d periods on a dairy farm near Hanford (CA, USA). Four 'high group' pens were used (i.e., cows which had cleared the fresh pen but were not yet confirmed pregnant), each with similar to 310 early lactation multiparity cows/pen. The two total mixed rations contained 171 g/kg dry matter (DM) crude protein (CP), 55 g/kg fat, 335 g/kg neutral detergent fiber (aNDF) and 135 g/kg starch, and were the same except for inclusion of the CE at 4 g/cow/d in the treatment diet (CED). Average daily high temperatures during the study were 35 to 37 degrees C with lows of 16-17 degrees C. In general, cows showed mild heat stress, but CE feeding had no effect on respiration rate, panting score or rump temperature at any time of the day (i.e., 02:45, 09:15, 17:30 h). However at 02:45 h, a higher (P< 0.01) proportion of CED cows were lying (versus standing) compared with Control cows (68.6 versus 53.7 cows/100 cows), which is an indicator of reduced heat stress. Intake of DM (25.3 kg/d) and whole tract digestibility of CP (703 g/kg) and aNDF (510 g/kg) did not differ between treatments. Milk production (47.3 kg/d) and its fat and true protein levels (35.4, 28.6 g/kg) did not differ, and changes in body condition and locomotion scores were also not impacted by treatment. However mammary health improved based on lower SCC (somatic cell counts; P< 0.04) of CED versus Control cows (160,000 versus 196,000 cells/mu L), and lower linear SCC scores (P< 0.01; 2.12 versus 2.30). Feeding this CE to lactating dairy cows during summer heat decreased SCC with no impact on other aspects of performance. (C) 2015 Elsevier B.V. All rights reserved.