Cooling and forage supplementation of grass-fed Holstein cows during hot conditions.

An experiment (108 days) was conducted to examine effects of cooling and forage supplementation on the performance of grass-fed, early lactation Holstein cows in a coastal, subtropical environment during summer. When the temperature-humidity index (THI) between 09:00 and 14:00 was <72, cows grazed pastures containing shade. When THI reached 72 during this time, the following treatments were imposed: pasture (P), cows remained in paddocks; feedpad (FP), cows were moved to a shaded feedpad with sprinklers; feedpad plus hay (FPH), as for FP and fed 3 kg dry matter/cow per day of lucerne hay. When intervention occurred (55 days), average THI (09:00-15:00) was 78 +/- 0.6; mean cow rectal temperatures for FP and FPH were lower than for P (-1.0 degree C and -0.9 degree C, respectively); respective daily yields of milk and protein per cow were higher (p < 0.06) for FPH (22.7 L; 666 g) than for FP (21.1 L; 609 g) and P (20.9 L; 600 g). It was concluded that the energy intake of Holstein cows in this environment is a greater limitation to milk production than intermediate heat loads. Supplementation with lucerne hay during these conditions will increase milk yield. Using sprinklers in addition to shade will improve cow comfort, but will not necessarily improve milk yield.