Effects of an electrolyte, energy, and osmolyte compound and heat stress on productivity in early-lactation Holstein cows.

Heat stress affects milk production and intake of dairy cattle. Strategies to mitigate the effects of heat stress suggest dietary supplements including electrolyte, energy, and osmolyte compounds (such as Bovine BlueLite, TechMix, Stewart, MN, which is a blend of these compounds), but direct and long-term evaluation of this supplement in lactating cows is needed. We hypothesized that the supplement would improve productivity of dairy cows (∼52 DIM) under heat stress. Cows (n = 52) were enrolled into a 4-wk 2 × 2 factorial arrangement as follows: (1) heat stress control (HT-CON, n = 13), (2) heat stress plus supplement (HT-SUP, n = 13), (3) cooling control (CL-CON, n = 13), and (4) cooling plus supplement (CL-SUP, n = 13). Cows were housed in a freestall barn. Supplement treatment was top-dressed on TMR (56.5 g/cow in the morning and 56.5 g/cow in the afternoon feeding). Evaporative cooling was provided to cows in the cooling groups, whereas heat-stressed cows only had shade. Milk yield, DMI, rectal temperature (RT), and respiration rate (RR) of individual cows were recorded during the study. Furthermore, milk contents of fat, protein, and lactose were measured weekly. Heat stress increased RR and RT relative to the cooling groups. Heat stress reduced DMI (HT = 20.3, CL = 24.5 ± 0.4 kg/d; ± SE), and supplementation reversed some of the effects in heat-stressed cows (HT-SUP = 20.9, HT-CON = 19.6 ± 0.5 kg/d) but did not affect cooled cows. The ECM yield was also decreased by heat stress (HT = 38.1, CL = 42.6 ± 0.8 kg/d), and supplementation partially reversed that effect in HT-SUP relative to HT-CON (HT-SUP = 39.6, HT-CON = 36.5 ± 1.1 kg/d). No main effects were observed for milk components, cortisol, or heat shock protein plasma concentration. Results suggest that supplementation partially mitigated the effects of heat stress on DMI and ECM in lactating dairy cows.