The defoliation dynamics of a stockpiled native grassland pasture follow similar patterns between supplemented and unsupplemented beef calves

Abstract

It is unclear to what extent and on which variables does supplementing beef cattle on native grasslands affect sward structure, specifically on the dynamics of its grazing horizons. Three hypotheses were tested: (i) during a grazing down process under similar forage allowance, supplemented animals take longer to finish each grazing stratum, than their unsupplemented counterparts, (ii) in both cases, the upper stratum will be heavily depleted before the subsequent strata are grazed, (iii) some species and/or forage fractions are consumed faster than others, regardless of the animals being supplemented (corn dried distillers grains with solubles, DDGS, at 0.7% of their body weight, BW, on a dry matter, DM, basis) or not. Three blocks of stockpiled native grasslands were used and split into two treatments plots (n = 6), on which either supplemented (S) or control (C) heifers of 10.6 ± 0.6 months of age and an initial BW of 143 ± 9 kg, were used. A 2.5 Â 0.5 m observation grid was installed on the sward, generating 384 observation points on each plot. On these observation plots, sward height (SH) and visually assessed green forage mass percentage (%G) were registered every other day for 12 consecutive days. No differences were found between the horizontal grazing dynamics between supplemented and control animals

Beef Cattle Grazing Native Grasslands May Follow Three Different Supplement Response Patterns

“…It was possible to observe different phases over time (Figure 2), in which all experiments presented at least one phase in which the BW change over time of C and S animals behaved oppositely, where S animals were actively gaining BW while C animals were maintaining or losing BW. In a grazing-down experiment, Cazzuli et al [30] could not find any differences between S and C animals concerning change in green content over time of their swards nor on their plant functional types' species preferences. This suggests that the differences in BW change between C and S animals in this work-especially of C animals' BW change-may be only partially explained by herbage quality or species composition of the sward throughout the duration of the trials.…”

“…The top leafy stratum of pastures is expected to be preferred among all other pasture components [37], meaning that it would be consumed before the rest of the sward, and therefore, the green leaf content would be expected to decline throughout trials. Even though Cazzuli et al [30] found an opposite trend-at least at the end of a long stockpiling period and before grazing activities began-Benvenutti et al [37] found that the fCP content of a C4 species dominated sward was greater in the upper stratum of the sward. Should the latter be the case, during the final phases, the pastures would be offering lower quality forage in terms of fCP, which matches our results because, during this late stage, the lower the fCP, the greater the response.…”