Effect of feed-bunk sprinklers on attendance at unshaded feed bunks in drylot dairies

This study determined the effect of feed-bunk-mounted sprinklers, temperature humidity index (THI), and wind speed on feed-bunk attendance. Bunk attendance of lactating Holstein cows was quantified at unshaded feed bunks in pens (n = 3) equipped with sprinklers that periodically sprayed the backs of the cows as they fed or in pens (n = 5) without sprinklers. The number of cows per pen ranged from 135 to 408. Proportion of total pen population within 2 m of the feed bunk (attending) was recorded at 2-h intervals over one 72-h period in August of 2007 and two 48-h periods in mid July and late August of 2008. Proportion of cows attending the bunk was analyzed in a mixed model using time of day as the dependent variable and with treatment as a response variable with observation period, DIM, and lactation as random effects. The effect of THI and wind speed was modeled using linear regression, with THI and wind speed being independent predictors. Mean THI was 74 ± 6 (SE) in 2007 and 73 ± 4.6 (SE) in 2008. There was no overall treatment effect (P = 0.76), but there was a time-bytreatment interaction (P = 0.001), where cows from pens equipped with sprinklers above the feed bunk increased attendance earlier in the afternoon when fresh feed was offered. Cows from pens without sprinklers began feeding later in the day after THI had decreased. Wind speed increased bunk attendance in pens with feed bunk sprinklers (P < 0.01) but not in pens without sprinklers (P = 0.30). The sprinklers increased attendance during hotter times of the day but did not affect daily bunk attendance.