160 Comparison of native to introduced mixed warm-season grass pastures on heifer weight gain and fecal egg count

Abstract The objective of this study was to compare summer body weight gain and fecal egg count change of spring weaned heifers grazing either native grass (NG; predominately big bluestem Andropogon gerardii)) or mixed warm-season grass (MWS; predominately bermudagrass (Cynodon dactylon) and crabgrass (Digitaria sanguinalis). Pastures (n = 3 per treatment and 2.02 ha each) were continuously stocked with 10 heifers each in yr 1 and 2, respectively. All pastures received 56 kg/ha N mid-May. Grazing began at the end of May and all pastures were grazed for 84 d. Heifers were previously treated with an anthelmintic at weaning (benzimidazole in yr 1 and macrocyclic lactone plus benzimidazole in yr 2). Dependent responses were analyzed for the fixed effect of treatment, year, and their interaction and random effect of pasture. Pasture was the experimental unit. Fecal egg counts as eggs per gram were transformed to a log base 10 value (log10:epg). Average daily gain differed between treatments by year (P = 0.05). In yr 1, NG gained 0.22 kg/d more than MWS; whereas, in yr 2, NG gained 0.11 kg/d more than MWS. Heifers grazing NG were 15.9 ± 3.52 kg heavier than MWS by d 84 (P = 0.01). Change in fecal egg count differed by year (P 0.001) and tended to be less for NG compared with MWS (P = 0.11). Native grass fecal egg count change was 45% of MWS. Impact of forage system on internal parasite load may be attributed to canopy structure. Native grasses averaged 67 and 81 ± 2.3 cm at the beginning of grazing in yr 1 and 2, respectively (P = 0.01). Native grass height in yr 1 and yr 2 was similar (P = 0.68) by wk 12 and averaged 41 ± 3.2 cm. By comparison, grazing in the MWS system would be much closer to the soil surface. Initial forage mass and forage mass change was greater in NG than MWS and differed by year (treatment × year P = 0.02 and 0.05, respectively). While this study demonstrated beneficial responses to grazing NG over MWS during summer months, further information regarding how these summer forage options compare under varied stocking rate and grazing duration is warranted.