Effects of Fescue Type and Sampling Date on the Nitrogen Disappearance Kinetics of Autumn-Stockpiled Tall Fescue,

Abstract

Two tall fescue [Lolium arundinaceum (Schreb.) Darbysh] forages, one an experimental host plant/endophyte association containing a novel endophyte that produces low or nil concentrations of ergot alkaloids (HM4) and the other a typical association of Kentucky 31 tall fescue and the wild-type endophyte (Neotyphodium coenophialum; E+), were autumn-stockpiled following late-summer clipping and fertilization with 56 kg/ha of N to assess N partitioning and ruminal disappearance kinetics of N for these autumn-stockpiled tall fescue forages. Beginning on December 4, 2003, sixteen 361 +/- 56.4-kg replacement dairy heifers were stratified by weight and breeding, and assigned to one of four 1.6-ha pastures (2 each of E+ and HM4) that were strip-grazed throughout the winter. Pastures were sampled before grazing was initiated (December 4), each time heifers were allowed access to a fresh pasture strip (December 26, January 15, and February 4), and when the study was terminated (February 26). Generally, fescue type and the fescue type x sampling date interaction exhibited only minor effects on total forage N, or partitioning of N within the cell solubles or the cell wall. For pregrazed forages, concentrations of N and N partitioned within the cell solubles both declined in a strongly linear relationship with sampling dates. In contrast, concentrations of cell-wall-associated N changed in erratic and often higher-ordered relationships with time, but the magnitude of these responses generally was limited. Unlike the partitioning of N within cell-wall and cell-soluble fractions, kinetic characteristics of ruminal N disappearance frequently exhibited interactions of fescue type and sampling date. For pregrazed forages, these included interactions for all response variables, and for postgrazed forages, fractions B and C, as well as rumen degradable protein. Ruminal disappearance rate for pregrazed E+ and HM4 exhibited quadratic (range = 0.057 to 0.082/h) and cubic (range = 0.057 to 0.075/h) relationships with time, respectively. For postgrazed E+ and HM4 forages, ruminal disappearance rate was unaffected (mean = 0.066/h) or only tended to be affected by sampling date (mean = 0.065/h), respectively. Concentrations of rumen degradable protein exhibited various curvilinear relationships with sampling dates, but disappearance was consistently extensive, and the overall range was relatively narrow (71.3 to 78.9% of N). These findings suggest that ruminal disappearance of N for autumn-stockpiled tall fescue forages remains extensive throughout the winter months and is only affected minimally by fescue type, sampling date, and grazing status.

In situ rumen degradation kinetics as affected by type of pasture and date of harvest

“…Furthermore, ED with passage rate of 0.08 h −1 decreased from DH1 to DH3 for NNF; was similar between DH2 and DH3 for NF; similar for DH1 and DH2, and higher than DH3; and higher in DH2 for MIXED (DH2>DH1>DH3). These fi ndings disagree with Flores et al (2008) and Salaun et al (1999) who suggest that estimates of cpED for autumn are comparable to those observed typically for early spring growth. The lower cpED may be related to environmental factors such as rainfall, temperature and light, e.g.…”

Composition chimique, dégradabilité in sacco et produits de fermentation in vitro de la fétuque élevée (<i>Festuca arundinacea</i.)

“…Plusieurs études menées aussi bien in vitro qu'in vivo ont montré qu'en général, les concentrations de NH3 dans le rumen comprises entre 30 et 80 mg N/l suffisent à assurer la protéosynthèse microbienne maximale (Satter et Slyter, 1974;Durand, 1982 ;Song et Kennelly, 1990). Preston et Leng (1987) de même que Flores et al (2008) (Misson, 1990 ;Teguia et al, 1999). Il existe une variabilité entre les écotypes de F. arundinacea quant à leur dégradabilité.…”

“…Elle s'adapte aussi bien aux régions chaudes, froides, humides que sèches (Horst et Nelson, 1979 ;King et Bush, 1985 ;Carrow et Duncan, 2003 ;Hoveland, 2009). Malgré ces mutiples qualités, les défauts majeurs de la fétuque élevée sont sa médiocre appétibilité et sa faible digestibilité (Emile et al, 1992 ;Kallenbach et al, 2003 ;Flores et al, 2008 Afin de caractériser le milieu ruminal du mouton d'expérimentation au cours de l'évaluation de la dégradabilité in sacco, le pH et la concentration en azote ammoniacal (N-NH3) dans le jus du rumen ont été mésurés comme suit : Juste avant le repas du matin (0 h), 1, 3 et 7 h après. L'azote ammoniacal a été dosé par la méthode de microdiffusion de Conway (Conway, 1957).…”