In vitro fermentation and digestion characteristics of shrubs Leucophyllum frutescens and Zanthoxylum fagara browsed by White-tailed deer (Odocoileus virginianum Texanus)
Native vegetation in northeastern Mexico is mainly composed by shrubs and small trees, which are browsed by white-tailed deer. The aim of the study was to determine, seasonally, the in vitro fermentation profiles of Leucophyllum frutescens and Zanthoxylum fagara. Foliage was sampled from summer 2005 to spring 2006 for a total of four consecutive seasons in two country sites: Linares and Los Ramones in the state of Nuevo Leon, Mexico. In vitro gas production was recorded at 3, 6, 9, 12, 24, 48, 72 and 96 h. As inoculum, rumen fluid from fistulated sheep was utilized. Microbial protein, ME content and in vitro organic matter digestibility (IVOMD) were also evaluated. Data were analyzed according to a multi-factorial arrangement being sites (2), shrubs (2) and seasons (4) the factors. Kinetic parameters significantly varied among shrubs, sites and seasons. The asymptotic gas production (B) ranged from 149 ml of gas/g DM in L. frutescens in summer 2005 in Los Ramones to 273 ml of gas/g DM in Z. fagara in winter 2006 in Linares country. The rate of gas production (c) was the lowest in L. frutescens in spring 2006 (0.028 %/h) while the highest (0.104 %/h) in Z. fagara collected in summer 2005 in Los Ramones. Values regarding lag phase (L) ranged from 0.64 to 2.07 h; in general, this variable was superior during spring seasons in both sites. Interactions sites x shrub species x seasons were significant (P < 0.001) for all kinetic parameters except for L. Microbial protein synthesis measured as purines varied significantly among sites, shrubs and seasons. Mean values ranged from 2.76 to 10.91 µmol, the latter was registered in L. frutescens collected in spring 2006 in Linares. The same scenario was registered with the ME content where values varied from 0.66 to 2.60 Mcal/kg DM. Estimates of IVOMD ranged from 56.8 to 93.1%. In general, highest digestibility values were registered in Z. fagara. Significant interactions related to IVOMD were registered as well. Data suggested that regardless spatio-temporal variations, variables such as constant rate of gas production, ME and microbial protein synthesis support the nutritive potential of the studied shrub species specially during the summer and autumn seasons for white-tailed deer.
Keywords: gas production, semiarid regions, white-tailed deer