Relay Intercropping Winter Cover Crop Effects on Spring Forage Potential of Sweet Maize Stover and Yearling Cattle Beef Performance.

Small landholders who grow sweet maize for the fresh produce market often also have cattle with little access to winter forage. Grazing cover crops with sweet maize stover can potentially increase the available nutritive value. A 3-year randomized complete block study with three replicates at New Mexico State University's Alcalde Sustainable Agriculture Science Center compared sweet maize (Zea mays var. rugosa) with sweet maize relay intercropped at the V7−9 stage with cereal rye (rye: Secale cereale L.) or hairy vetch (vetch: Vicia villosa Roth) for early spring grazing. Intercropping the rye or hairy vetch into sweet maize did not influence the sweet maize stover biomass yield or nutritive value after the winter. The dry matter (DM) yield and crude protein (CP) concentration of hairy vetch biomass was greater (p < 0.01) than rye biomass (1.46 vs. 2.94 Mg DM ha−1 for rye and hairy vetch, respectively, and 145 vs. 193 g CP kg−1 for rye and hairy vetch, respectively). Average daily gains by yearling cattle were not different when grazing maize−rye or maize−vetch. Producers should consider the spring planting timing of the primary crop and the initiation of grazing in the winter or the spring to maximize the utilization of the previous crop's residue (stover), as well as the cover crop itself.

Contrasting above- and belowground sensitivity of three Great Plains grasslands to altered rainfall regimes.

Intensification of the global hydrological cycle with atmospheric warming is expected to increase interannual variation in precipitation amount and the frequency of extreme precipitation events. Although studies in grasslands have shown sensitivity of aboveground net primary productivity (ANPP) to both precipitation amount and event size, we lack equivalent knowledge for responses of belowground net primary productivity (BNPP) and NPP. We conducted a 2-year experiment in three US Great Plains grasslands--the C4-dominated shortgrass prairie (SGP; low ANPP) and tallgrass prairie (TGP; high ANPP), and the C3-dominated northern mixed grass prairie (NMP; intermediate ANPP)--to test three predictions: (i) both ANPP and BNPP responses to increased precipitation amount would vary inversely with mean annual precipitation (MAP) and site productivity; (ii) increased numbers of extreme rainfall events during high-rainfall years would affect high and low MAP sites differently; and (iii) responses belowground would mirror those aboveground. We increased growing season precipitation by as much as 50% by augmenting natural rainfall via (i) many (11-13) small or (ii) fewer (3-5) large watering events, with the latter coinciding with naturally occurring large storms. Both ANPP and BNPP increased with water addition in the two C4 grasslands, with greater ANPP sensitivity in TGP, but greater BNPP and NPP sensitivity in SGP. ANPP and BNPP did not respond to any rainfall manipulations in the C3 -dominated NMP. Consistent with previous studies, fewer larger (extreme) rainfall events increased ANPP relative to many small events in SGP, but event size had no effect in TGP. Neither system responded consistently above- and belowground to event size; consequently, total NPP was insensitive to event size. The diversity of responses observed in these three grassland types underscores the challenge of predicting responses relevant to C cycling to forecast changes in precipitation regimes even within relatively homogeneous biomes such as grasslands.

Effects of rumen-protected methionine on plasma amino acid concentrations during a period of weight loss for late gestating beef heifers.

This study determined changes in plasma amino acid concentration in late-gestating (beginning 58 ± 1.02 days prior to calving), primiparous, winter-grazing range heifers receiving wheat middling-based supplement without (CON) or with rumen-protected methionine (MET) to provide 15 g DL-MET each day. Plasma was collected on days -2 and 0 (start of MET supplementation just prior to individually receiving supplement at 0700 hours). Plasma was sampled again on days 40, 42 and 44 prior to supplementation at 0700 and 1100 hours (4 h after receiving daily supplement). Data were analyzed with cow as the experimental unit. Continuous variables were analyzed by the main effects of treatment, date, or time and their interaction when appropriate. Comparable BW (P = 0.32) and BCS (P = 0.83) over the 44-day metabolism trial were found between both CON- and MET-fed heifers. MET-supplemented heifers had greater (P < 0.01) plasma concentrations of methionine indicating that the rumen-protection technology successfully delivered methionine to the small intestine. Supplementation with rumen-protected DL-MET caused a significant supplement × date interaction for glutamine (P = 0.03), glycine (P = 0.02), methionine (P < 0.01), and serine (P = 0.05). In addition, trends for supplement × date interactions were detected for leucine (P = 0.07), threonine (P = 0.09), valine (P = 0.08), total amino acids (TAA; P = 0.08), non essential amino acids (NEAA; P = 0.08), branched chain amino acids (BCAA; P = 0.08), and glucogenic amino acids (GLUCO; P = 0.08). These results suggest that the BCAA (leucine and valine) were utilized more efficiently with MET supplemented heifers compared to CON supplemented heifers. Plasma AA concentrations for glutamic acid (P < 0.01), histidine (P = 0.01), tyrosine (P < 0.01), and EAA (P < 0.01), all decreased throughout the study. These results further confirm methionine is a limiting amino acid in forage fed late-gestating heifers and further suggests the limitation when grazing dormant range forages as shown by improved utilization of other plasma amino acids when supplemental methionine was provided.

Determination of methylglyoxal in ruminal fluid by high-performance liquid chromatography using fluorometric detection.

There is no reported method for the quantification of methylglyoxal in ruminal fluid. The method reported here is based on the conversion of methylglyoxal to 6-methylpterin, followed by quantification of the resulting pteridinic compound by fluormetric detection using liquid chromatography. Ruminal fluid was collected and preserved with 1 M HCl at -20 degrees C. Cation exchange prior to derivatization was used to eliminate possible interfering peaks. The detection limit of 0.125 microg/mL was calculated. The recoveries were >80%, and the coefficients of variation were <15%. This method has proven to be rugged and accurate for the detection of methylglyoxal concentration in ruminal fluid collected from cows fed diets deficient in degradable intake protein as a marker. Methylglyoxal is produced by ruminal bacteria in response to low nitrogen levels in the rumen. The ruminal methylglyoxal concentration has the potential to be a useful marker to assess ruminal nitrogen status to aid in more accurate diet formulation.