Preference and Selection by Beef Cattle Grazing Diverse Forages in Resource Islands Embedded in Grass Monocultures

Abstract

Beef cattle on rangelands typically graze grass monocultures that become nutritionally and phytochemically constrained during summer, reducing animal performance and health. We tested whether patches of forages (i.e., “islands”) embedded within smooth bromegrass (SBG) paddocks enable cows to self-select complementary forages that may improve animal performance. Fifteen Angus cow–calf pairs grazed three SBG paddocks (five pairs/paddock), each with three 30 × 40 m forage islands (three islands/paddock) comprising adjacent strips of alfalfa-ALF, sainfoin-SF, forage kochia-KH, small burnet-SB, and a patch of mixed weeds-MW. Across three 15-day periods, cows accessed one island/paddock for 1 h each evening. Cows were video-recorded simultaneously, and the forage species grazed by each cow was recorded at 2-min intervals using instantaneous scan sampling. Caged biomass quantified proportional forage availability for preference–biomass comparisons and availability-based multispecies indices, while scan-based preference was analysed using binomial GLMMs, FSI using a linear mixed-effects model, and the remaining selectivity, forage-mixing, and turnover indices descriptively. Scans on forage use shifted across periods (p < 0.001): scans on MW declined from 30%–35% to 15%–20% of total scans, while those on SF and ALF increased to 25%–30% and 15%–20%, respectively. SF had the highest overall selection ratio (w = 1.53), and ALF shifted from avoidance to positive selection. Within bouts, FSI peaked early, then declined as the diversity of forage items selected increased; MS trended toward 0, and turnover decreased. Forage islands promoted cattle preference and selectivity for nutrient- and phytochemical-rich legumes and broadened dietary choice within SBG monoculture paddocks, potentially supporting their health and performance while reducing environmental impacts.