Effect of post-weaning development method on spring grazing patterns of rangeland beef heifers

Abstract

We determined the influence of post-weaning development method on rangeland grazing patterns of beef heifers during early and late spring. We compared behavior of heifers wintered on rangeland (group-fed cake, GFC or self-fed protein, SFP supplements during winter) or in a pen where they were fed silage (pen-fed silage, PFS). In April and May of each year (n = 3), heifers (n = 95) were fitted with Lotek 3300LR GPS collars and monitored 18 days each month. PFS heifers traveled farther than SFP and GFC counterparts on the first few days in April (P < 0.05). PFS heifers covered larger areas of the pasture compared to GFC and SFP (P < 0.05) counterparts during May. All heifers followed trajectories of similar sinuosity (P > 0.05). On most days, PFS heifers allocated more time to resting (April) and traveling (April and May) than heifers in SFP treatment (P < 0.05). SFP heifers spent significantly more time grazing than PFS and GFC counterparts during April (P < 0.01). However, differences in foraging patterns decreased through time. All heifers spent more time grazing (P < 0.01) on cloudy days with higher humidity during April and less time grazing on windy and rainy days in May (P < 0.05). Pixel Normalized Difference Vegetation Index (NDVI) appeared to influence pasture use patterns regardless of treatment. Traveling and resting time, as well as pixel residence time were the three variables that best discriminated heifers into treatment groups (P < 0.01). Collared heifers tended to associate with heifers of their own/other treatment group (prevailing PFS-GFC or GFC-SFP heifers). The social role of a collared heifer in the herd did not appear to be associated with development treatment. Post-weaning development protocols modified movement, activity, and habitat use of heifers during early spring. Initial animal state and/or metabolic memory may have been responsible for the differences observed. Such differences, however, were possibly attenuated by social facilitation.