Cattle Grazing Preference Among Diploid and Tetraploid Annual Ryegrass Cultivars.

Determination of animal preference early in the evaluation process of new forages can be advantageous because of positive relationships with forage quality.  A 2-yr study was conducted at Raymond, MS to determine grazing preference of cattle between tetraploid and diploid annual ryegrass (Lolium multiflorum Lam.) cultivars and its relationship with morphological and chemical characteristics.  Treatments were two diploid entries ‘Marshall’ and ‘Gulf’ and two tetraploid entries ‘Maximus’ and ‘Nelson’ arranged in a 4 × 4 Latin square design experiment.  Plots were 10 × 10 m separated by 2-m alleyways.  Eight Angus crossbred yearling steers (initial body weight of 320 ± 19 kg) were assigned to graze the plots for 48-h durations every 28 d.  Animal preference was based on herbage disappearance, the Chesson-Manly (CM) index, and amount of time spent grazing.  Responses were considered different P < 0.05.  Herbage disappearance was greater for the tetraploid cultivars (1400 kg ha^-1) than diploids (890 kg ha^-1).  For both years, CM index was greater for the tetraploid cultivars than for the diploids (8.1 vs. 5.8%, 2011 and 6.9 vs. 5.5%, 2012).  Also, animals spent about 10% greater time grazing the tetraploid cultivars than diploids during both years.  During the first year, the tetraploid cultivars had lesser NDF (556 g kg^-1) than the diploids (589 g kg^-1).  Also, diploids had greater ADF (359 g kg^-1) than tetraploids (341 g kg^-1) and Nelson had greater WSC concentration (184 g kg^-1) than the other three entries (152 g kg^-1).  In the second year, NDF, ADF, and WSC were not different among entries.  Tetraploid cultivars had a greater proportion of leaf to stem (56%) than diploids (48%).  The results indicate that cattle showed greater preference for tetraploid entries, which appeared to be linked mainly with proportion of leaf, and this may lead to increased utilization efficiency of pastures.