Short communication: Relationship of activity and rumination to abundance of pest flies among organically certified cows fed 3 levels of concentrate

The objectives of this study were to evaluate activity, rumination time, and their association with 3 kinds of pasture flies for organic dairy cows (n = 57) fed 3 grain supplementation strategies during the grazing season from May to September 2013. Cows were assigned to 1 of 3 replicate supplementation groups: (1) no corn-grain supplementation (100% pasture, PAS, n = 19); (2) low corn-grain (2.72 kg/cow per day, LG, n = 19); and (3) high corn-grain (5.44 kg/cow per day, HG, n = 19). Cows calved during 2 seasons (fall and spring) at the University of Minnesota West Central Research and Outreach Center, Morris, from October to December 2012 and March to May 2013. Supplement (corn-grain and minerals) was fed in a total mixed ration of corn silage and alfalfa silage, and at least 30% of diet dry matter intake for LG and HG cows consisted of pasture. Activity and rumination time (daily and 2-h blocks of time) were monitored electronically using HR-LD tags (SCR Engineers Ltd., Netanya, Israel) for 125 d. Activity (cow body movement and head movement) was reported in activity units from SCR DataFlow II software, and rumination times were reported in minutes per day. PROC HPMIXED in SAS (SAS Institute Inc., Cary, NC) was used for statistical analysis, and independent variables were season of calving (fall or spring), month of grazing (June to September), supplementation group, and interactions of month of grazing and supplementation group. Replicate was a random effect with repeated measures. Daily activity was higher for PAS cows (1,138 activity units) than for HG cows (1,001 activity units), and LG cows (1,019 activity units). Daily activity was highest in July (1,258 activity units) and lowest in September (819 activity units). Rumination was not different for PAS (397 min/d), LG (384 min/d), or HG (370 min/d) cows. Daily rumination was greater in September (402 min/d) than in July (361 min/d). Daily activity increased rapidly between 0600-0800 h and 1600-1800 h. From 1800 to 2000 h, cows had a rapid decline in activity until 0600 h the next day. All supplementation groups had the greatest rumination activity from 0200 to 0400 h and the least between 1000 and 1200 h. Greater activity of cows on a herd basis was moderately correlated with increased fly populations. Monthly activity patterns of grazing cows were associated with fly populations on cows.