Optimizing feedstock production from switchgrass (Panicum virgatum L.) requires careful matching of genotype to environment, especially for southern U.S. regions. Nine genotypes from four combinations of ecotype and morphological type were harvested once yearly in autumn for 3 or 4 yr at five locations across Texas, Arkansas, and Louisiana that varied in latitude and precipitation. Genotypes were evaluated for dry matter yield (DMY), plant density, tiller density, lodging, and rust (caused by Puccinia spp.) infection. Genotype × environment (G×E) interactions were identified for most traits. Biomass yield of all genotypes tended to increase with latitude, but lowland morphological types may have been more sensitive than upland morphological types to differences in moisture availability. Yield (5.82 vs. 14.97 Mg ha−1, respectively) and persistence (final stand density, 3.99 vs. 5.96 plants m−2) were lower for upland than for lowland genotypes, particularly at higher rainfall and more southern sites. Lowland genotypes were often able to compensate for stand thinning by increasing individual plant size, but upland genotypes were not. Lodging and rust scores were higher for upland than for lowland genotypes. Yield (13.65 vs. 9.75 Mg ha−1) and final plant density (5.58 vs. 4.95 plants m−2) were higher for southern than northern ecotypes. The southern‐lowland combination exhibited the best yield and persistence over the study region, and genotypes within this group exhibited variability in yield among sites. Therefore, development of switchgrass cultivars for biomass production in the southern USA should focus on the southern‐lowland genotypes.
Choice of forage species and harvest management may influence protein degradability in cattle diets. We measured forage yield, undegradable intake protein (UIP), and forage quality at three maturities in two cuttings (spring, regrowth) of alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), and birdsfoot trefoil (Lotus corniculatus L.) in the seeding and two subsequent years. At equivalent harvest stage, trefoil and clover were usually lower in neutral detergent fiber (NDF) and acid detergent fiber (ADF) than alfalfa. Crude protein (CP) was lower in red clover than trefoil or alfalfa for three of six cuttings, but red clover was equal to or higher in UIP than alfalfa or trefoil in all cuttings. Trefoil never had higher UIP concentrations than alfalfa. Trefoil tannin concentrations increased with maturity and were positively correlated with UIP concentration. For all species, UIP was positively correlated with NDF and ADF and negatively correlated with in situ dry matter disappearance (ISDMD). In alfalfa and trefoil, UIP was negatively correlated with CP. In all legumes, dry matter yield (DMY), NDF, and ADF increased with maturity, while CP and ISDMD decreased. Changes in NDF, ADF, CP, and ISDMD with maturity were usually most rapid in trefoil. The proportion of UIP increased with maturity for all species in all cuttings, but it never comprised more than 240 g kg−1 CP. Small increases in UIP as legumes matured were gained at the expense of other forage quality measures.
Nutritive value of alfalfa (Medicago sativa L.) is limited by indigestible cell wall constituents, especially lignin. Commercially released genetically engineered alfalfa cultivars with reduced lignin (RL) concentration were developed recently by downregulation of the caffeoyl CoA 3‐O‐methyltransferase (CCoAOMT) enzyme in the lignin pathway. This research compared forage nutritive value and dry matter yield of a RL cultivar (‘HarvXtra‐008’) with non‐RL cultivars (‘54R02’ and ‘WL355RR’) across six states in the northern United States. A randomized complete block design with a split‐plot restriction on treatment randomization was used, where harvest intervals (28, 33, and 38 d) were assigned to whole plots and cultivars were the subplots. Harvest interval and cultivar effects were significant (P < 0.001) for all variables, and cultivars responded similarly across harvest intervals in that forage yield increased and nutritive value declined with increasing harvest interval. HarvXtra‐008 was consistently greater in forage nutritive value than non‐RL cultivars averaged across harvest intervals: it was 8.4% lower in acid detergent lignin, 3.5 to 7.5% lower in amylase‐treated neutral detergent fiber, and 5.3 to 7.7% greater in neutral detergent fiber digestibility, but 4.8 to 7.0% lower in dry matter yield. HarvXtra‐008 was slightly higher or similar in nutritive value and had similar or greater dry matter yield compared with non‐RL cultivars harvested on a harvest schedule 5 to 10 d earlier and more frequent. Thus, RL alfalfa can extend the time interval when it is possible to harvest forage with adequate fiber digestibility for animals with high energy requirements.
Salivation rates were measured by cardial collection in four ruminally fistulated, early lactation cows. Complete diets of 70% concentrate: 30% hay crop silage (dry matter) or an isonitrogenous, isocaloric mixture of 60% concentrate: 40% corn silage were fed ad libitum once daily in a replicated 2 X 2 Latin square design. Thirty-day periods, beginning 2 d postpartum, consisted of 22 d adaptation and 8 d for determination of eating behavior, eating and resting salivation rates, and rumen liquid turnover rate. Diet did not affect eating behavior, salivation rates, saliva volumes produced while eating or resting, or saliva composition, but degree of feed ensalivation (fresh basis) and volume of saliva per bolus were higher for the hay crop silage diet due to its higher dry matter content. Resting salivation rate and volume produced while resting were greater at wk 8 than wk 4 of lactation even when corrected to constant dry matter intake, indicating that adaptation to diet postpartum involved increased basal resting salivation rate. Rumen pH was lower for the hay crop silage diet, but rumen fluid kinetic measurements did not differ with diet or week of lactation.
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