Evaluation of warm season annual forages for forage yield and quality in the north-central United States.

Grazing-based dairy operations require productive, high-quality forages capable of supporting the nutritional needs of mid-lactation dairy cows. Our objectives were to evaluate primary and regrowth harvests of two cultivars of sudangrass (SU), sorghum-sudangrass (S×SU), and pearl millet (PM) forages for growth and nutritive characteristics within the specific context of suitability for grazing by dairy cows. Three harvest cycles, including primary and regrowth cycles in 2016, and a single harvest cycle of primary growth in 2017, were evaluated at two locations (Prairie du Sac and Marshfield, WI). Within each cycle, sampling was initiated when canopy height was about 41 cm and continued thereafter on weekly intervals for 5 weeks, resulting in six equally spaced sampling dates per harvest cycle. Data were analyzed as a split-plot design with cultivars (6) as whole-plots arranged in randomized complete blocks and weekly harvest dates (6) as subplots. Yields of dry matter (DM) were less consistent at the more northern location (Marshfield), which is known for its heavier, poorly drained soils. Despite locational differences, the taller-growing cultivar within each forage type frequently exhibited yield advantages over dwarf or shorter-growing cultivars; this occurred for 7 of 9 intra-forage-type comparisons (P ≤ 0.021) across three harvest cycles at Prairie du Sac, and for 6 of 9 similar comparisons (P ≤ 0.032) at Marshfield. In 2016, shorter-growing cultivars had greater percentages of leaf in 4 of 6 intra-forage-type comparisons at both locations (P ≤ 0.004), which is especially relevant for grazing. Similarly, PM cultivars exhibited shorter canopy heights (P ≤ 0.002), but greater percentages of leaf (P < 0.001), than all other cultivars during all harvest cycles at both locations. However, the greater leaf percentages exhibited by PM cultivars did not translate into reduced percentages of structural plant fiber (asNDFom) on a whole-plant basis during any harvest cycle at either location; furthermore, asNDFom concentrations for PM cultivars were greater (P ≤ 0.047) than observed for other cultivars within 3 of 6 harvest cycles across both locations. Ruminal in-situ degradation of asNDFom for whole-plant forages based on a 48-h incubation was significantly greater (P ≤ 0.006) for PM compared with other cultivars in 4 of 6 harvest cycles. Pearl millet cultivars generally exhibited more suitable characteristics for grazing livestock than SU or S×SU cultivars.

Beef cattle responses to pre-grazing sward height and low level of energy supplementation on tropical pastures.

The objective of this study was to investigate the effects of energy supplementation and pre-grazing sward height on grazing behavior, nutrient intake, digestion, and metabolism of cattle in tropical pastures managed as a rotational grazing system. Eight rumen-cannulated Nellore steers (24 mo of age; 300 ± 6.0 kg body weight [BW]) were used in a replicated 4 × 4 Latin square design. Treatments consisted of two levels of energy supplementation (0% [none] or 0.3% of BW of ground corn on an as-fed basis) and two pre-grazing sward heights (25 cm [defined by 95% light interception (LI)] or 35 cm [defined by ≥ 97.5% LI]) constituting four treatments. Steers grazed Marandu Palisadegrass [Brachiaria brizantha Stapf. cv. Marandu] and post-grazing sward height was 15 cm for all treatments. Forage dry matter intake (DMI) was increased (P = 0.01) when sward height was 25 cm (1.86% vs. 1.32% BW) and decreased (P = 0.04) when 0.3% BW supplement was fed (1.79% vs. 1.38% BW). Total and digestible DMI were not affected by energy supplementation (P = 0.57) but were increased when sward height was 25 cm (P = 0.01). Steers grazing the 25-cm sward height treatment spent less time grazing and more time resting, took fewer steps between feeding stations, and had a greater bite rate compared with 35-cm height treatment (P < 0.05). Energy supplementation reduced grazing time (P = 0.02) but did not affect any other grazing behavior parameter (P = 0.11). Energy supplementation increased (P < 0.01) diet dry matter digestibility but had no effect on crude protein and neutral detergent fiber digestibilities (P = 0.13). Compared with 35-cm pre-grazing sward height, steers at 25 cm presented lower rumen pH (6.39 vs. 6.52) and greater rumen ammonia nitrogen (11.22 vs. 9.77 mg/dL) and N retention (49.7% vs. 20.8%, P < 0.05). The pre-grazing sward height of 25 cm improved harvesting efficiency and energy intake by cattle, while feeding 0.3% of BW energy supplement did not increase the energy intake of cattle on tropical pasture under rotational grazing.

Bacterial communities in the rumen of Holstein heifers differ when fed orchardgrass as pasture vs. hay.

The rich and diverse microbiota of the rumen provides ruminant animals the capacity to utilize highly fibrous feedstuffs as their energy source, but there is surprisingly little information on the composition of the microbiome of ruminants fed all-forage diets, despite the importance of such agricultural production systems worldwide. In three 28-day periods, three ruminally-cannulated Holstein heifers sequentially grazed orchardgrass pasture (OP), then were fed orchardgrass hay (OH), then returned to OP. These heifers displayed greater shifts in ruminal bacterial community composition (determined by automated ribosomal intergenic spacer analysis and by pyrotag sequencing of 16S rRNA genes) than did two other heifers maintained 84 d on the same OP. Phyla Firmicutes and Bacteroidetes dominated all ruminal samples, and quantitative PCR indicated that members of the genus Prevotella averaged 23% of the 16S rRNA gene copies, well below levels previously reported with cows fed total mixed rations. Differences in bacterial community composition and ruminal volatile fatty acid (VFA) profiles were observed between the OP and OH despite similarities in gross chemical composition. Compared to OP, feeding OH increased the molar proportion of ruminal acetate (P = 0.02) and decreased the proportion of ruminal butyrate (P < 0.01), branched-chain VFA (P < 0.01) and the relative population size of the abundant genus Butyrivibrio (P < 0.001), as determined by pyrotag sequencing. Despite the low numbers of animals examined, the observed changes in VFA profile in the rumens of heifers on OP vs. OH are consistent with the shifts in Butyrivibrio abundance and its known physiology as a butyrate producer that ferments both carbohydrates and proteins.