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

• A citrus extract fed to lactating cows had no impact on animal performance.
• Milk SCC count reductions with citrus extract feeding suggested improved mammary health.
• Naturally occurring bioactive compounds can impact animal performance.

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 × 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 ∼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 °C with lows of 16–17 °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/μL), 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.