Five hundred seventy Holstein dairy cows (280 primiparous and 290 multiparous; 194 DIM and 34.4 kg/d milk) from the commercial dairy farm El Trébol (Durango, México) were used to evaluate the effect of a sensory additive (ProEfficient, Lucta S.A.) on dry matter intake, milk production, and feed conversion efficiency under heat stress conditions in a completely randomized design. Cows were grouped by parity (primiparous vs. multiparous) in four free-stall pens and randomly assigned to two treatments: control TMR or the same TMR supplemented with 30 g/d of ProEfficient (PE). The TMR (52:48 concentrate: forage; 18.2% CP, 29.1% NDF, 42.1% NFC) was offered twice daily and PE was top-dressed at each feeding during 34 d starting on June 25tafter 2 wk of adaptation. Daily dry matter intake of each pen and individual milk yield (Alpro, De Laval) were measured. Data were analyzed by ANOVA with a mixed model with repeated measures using the PROC PROC MIXED of SAS (1999) where pen nested within treatment was considered as random effect. During the experimental period, maximum and minimum temperatures averaged 38.9 and 20.4°C, respectively. Dry matter intake increased 1.2 kg/d (23.6 vs. 24.8 kg/d; P < 0.05) with the inclusion of the PE additive. Cows fed the TMR with PE produced 2 kg/d more of milk (35.2 vs. 33.2 kg/d; P < 0.05) with similar feed conversion efficiency (1.42 kg milk/kg DMI; P > 0.05). Based on previous findings from studies with PE, the milk response to this additive could have been related to changes in ingestive behavior (meal size and frequency) and/or positive modulation of hormonal signals associated with the control of feed intake (e.g., ghrelin). Feeding a sensory additive under heat stress conditions increased dry matter intake and milk production of dairy cows fed a TMR.
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