GRAZING BEHAVIOR OF NEW ZEALAND HOLSTEIN COWS WITH ACCESS TO SHADE

Abstract

Access to shade decreases heat stress of grazing dairy cows, but may reduce their grazing time. It was hypothesized that access to shade would alter grazing behavior of New Zealand Holstein cows. The objective was to evaluate the distribution of time use of cows with and without access to shade in a temperate sub-humid climate with summer rainfall, where the mean annual temperature varies between 12 (January) and 18 °C (May). During the warm (May) and cool (October) seasons of 2017, two lots of nine lactating New Zealand Holstein cows grazed in two treatments, with (S) and without (NS) shade access. Behavior was recorded every 10 min for 5 d per period. The response variables were: grazing times; rumination standing, prostrate and total; resting standing, prostrate and total. The data were classified as diurnal (07:00 to 19:00 h) and nocturnal (19:00 to 07:00 h); the former were grouped into four shifts according to Temperature and Humidity Index (TIH) and solar radiation. It was analyzed with a general linear model and the MIXED procedure. In the warm season (19 °C. precipitation of 44.3 mm) cows with access to shade grazed 16 % less time (p ≤ 0.05) in the shifts of higher THI and solar radiation, being higher the percentage of shade use. During the cool season (16 °C, precipitation 62.0 mm) at times of higher THI (71.0) and solar radiation (880.5 Wm-2) S cows ruminated standing 44 % longer (p ≤ 0.05), with total rumination time 30.7 % longer (p ≤ 0.05) than NS; the latter rested standing 22.5 % longer (p ≤ 0.05). Access to shade modified the behavior of New Zealand Holstein cows grazing in the temperate climate of Mexico.