No abstract

Native forages such as trees Quercus eduardii and Quercus grisea; shrubs such as Atriplex canescens, Acacia constricta, Acacia shaffneri, Cassia wislizeni, Celtis pallida, Condalia lycioides, Cordia parvifolia, Flourencia cernua, Larrea tridentata, Mimosa biuncifera and Prosopis leavigata; forbs such as Coldenia greggii, Dalea bicolor, Jatropha dioica and Parthenium incanum; cacti such as Opuntia imbricata, Opuntia leptocaulis and Opuntia leucotricha; red and white fruits from O. leucotricha; fruits from O. leptocaulis, O. imbricata and A. canescens; pods from P. leavigata; pods from A. shaffneri and flowers from Yucca spp. were collected to estimate and compare the mineral content. Plant samples were collected during the dry and wet seasons of two consecutive years (2006Á2007) at seven locations situated in four counties of the state of Durango, Mexico. All macrominerals and trace elements were significantly different among plants within each group of plants. The Ca, Mg, K, Fe and Mn content of most plants were in sufficient amounts to satisfy adult range requirements; however, P, Na, Cu and Zn resulted with marginal deficiencies.

The objective of the study was to quantify differences in nutritive value, over four seasons, of native grasses such as <i>Bouteloua curtipendula, Bouteloua trifida, Brachiaria fasciculata, Chloris ciliata, Digitaria insularis, Leptochloa filiformis, Panicum hallii, Panicum obtusum, Paspalum unispicatum, Setaria grisebachii, Setaria macrostachya, Tridens eragrostoides, Tridens muticu</i>s and naturalized <i>chrus ciliaris</i> and <i>Rhynchelytrum repens</i> that are used as forages for grazing beef cattle. <i>Cenchrus ciliaris</i> was included as a reference grass of good nutritional quality. Plants were collected in autumn 2001 and in winter, spring and summer 2002. The nutritive value was assessed in terms of nutrient content, effective rumen degradable dry matter (EDDM), metabolizable energy (ME) and metabolizable protein (MP). Most grasses had crude protein (CP) content comparable to the reference <i>C. ciliaris</i> grass (grand mean = 120 g/kg) and some of them had a higher content (140 g/kg). Cell wall (NDF) and lignin contents were lower in <i>C. ciliaris</i> (650 g/kg, 30, respectively) than in the other grasses (mean = 700 g/kg, 60, respectively). All grasses had less EDDM (mean = 420 g/kg) than <i>C. ciliaris</i> (470 g/kg). All grasses had the ME content (mean = 5.6 MJ/kg DM) that was lower for maintenance requirements of growing beef cattle. Conversely, mean MP values (67 g/kg DM) were sufficient. Lower content of P (annual mean = 120 g/kg DM), Na (0.3) and Cu (40 mg/kg DM) was detected in all grasses to meet the requirements of growing cattle. All grasses, in all seasons, had sufficient CP and MP content to meet the maintenance requirements of growing beef cattle. Higher levels of EDDM occurred in summer and autumn. Because of their good nutritional quality, grasses such as <i>B. fasciculata, C. ciliata, P. hallii, P. obtusum, S. grisebachii, S. macrostachy</i> and <i>T. eragrostoides</i> can be considered as good forages for ruminants.

The aim was to determine effects of addition of polyethylene glycol (PEG) on in vitro gas production and microbial protein synthesis of the shrub species Acacia constricta, Acacia shaffneri, Calliandra eriophylla, Condalia lycioides, Cordia parvifolia, Larrea tridentata and Mimosa biuncifera, which are commonly consumed by grazing small ruminants in semiarid regions of Mexico despite the abundance of tannins in their foliage. Three individual samples (a minimum of 10 plants of each) of each shrub species were collected from different areas and prepared for chemical and secondary metabolite analysis. In vitro evaluations for each sample of each shrub species were completed in three incubation runs in different weeks using calibrated glass syringes in a 7 × 2 factorial design (i.e., 7 shrub species × 2 treatments with or without PEG). In vitro gas production after 24 and 96 h, partitioning factor (PF), metabolizable energy (ME) content, efficiency of microbial protein synthesis (EMPS), and volatile fatty acids (VFA) were determined. A shrub species × PEG interaction (P<0.05) only occurred for some VFA, such as C3, C4, C4i and C5i, concentrations. Relative to control, addition of PEG increased (P<0.05) the concentrations of individual VFA in A. shaffneri, C. lycioides and C. parvifolia. Interactions between shrub and PEG occurred (P<0.001) for all gas production parameters (i.e., b, k, IVGP 24 , IVGP 48). The fractional rate of gas production and IVGP 24 h were highest in A. constricta and lowest (P<0.001) in A. shaffneri. L. tridentata had the highest PF and C. lycioides the lowest. A. constricta had the highest ME content. Purine content and EMPS differed (shrubs × PEG; P<0.001) among shrubs. Microbial protein synthesis was highest in M. biuncifera and lowest in C. eriophylla, while total VFA were highest in C. eriophylla. Incorporation of PEG increased (P<0.

The objective of the study was to determine the chemical composition of the diet, intake and plasma concentrations of glucose, urea and non-esterified fatty acids (NEFA) during pregnancy in goats grazing a thorn scrubland of the semi-arid region of North Mexico. Additionally, monthly changes during pregnancy of plasma concentrations of luteinizing hormone (LH), growth hormone (GH), insulin (INS) and progesterone (P4) were also measured. A herd of 250 goats was bred in August and blood samples were collected from 12 goats at monthly intervals up to December to evaluate plasma glucose, urea, NEFA, LH, GH, INS and P4. Three goats fitted with oesophageal cannulae (38±1·7 kg BW) were used to obtain diet samples during pregnancy. Response variables were analysed by split-plot ANOVA for repeated measures on animals across time. When significant differences were observed among pregnancy months, multiple comparisons were performed using the PROC GLM-PDIFF option of SAS. The response variables organic matter (OM), crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), lignin, hemicellulose and cellulose differed across pregnancy. Mean values for the whole period were (g/kg DM) 866 (OM), 149 (CP), 524 (NDF), 364 (ADF), 131 (lignin), 160 (hemicellulose), and 233 (cellulose). Mean values for dry matter intake (DMI, kg/day), metabolizable energy intake (MEI, MJ/day) and metabolizable protein intake (MPI, g/day) were 1·2, 8·9 and 74·0, respectively and were different among periods of sampling (P<0·05). Mean plasma glucose concentration was 41±4·3 mg/dl with no significant differences (P>0·05) across pregnancy. Plasma NEFA concentrations increased (P<0·05) at the end of pregnancy (August, 0·396 v. November, 1·27 mM/l). Plasma urea concentrations were higher (P<0·05) in August (26·3 mg/dl) and November (26·2 mg/dl). Serum urea concentrations were related to MPI (r=0·82, P=0·10) and to the undegraded protein absorbed from the duodenum (r=0·79; P=0·07), but not with the rumen NH3-N concentration (r=−0·25; P=0·68). Hormone plasma concentrations differed (P<0·05) across pregnancy. While the largest serum LH concentration (P<0·05) was observed in mid pregnancy (October, 7·8 ng/ml), the lowest value was depicted at the end of gestation (4·8 ng/ml). A similar pattern was observed in plasma P4, with monthly increases from August to November, and a reduction during the last month of gestation (August, 5·6 v. December 2·5 ng/ml). With respect to the metabolic hormones, a negative correlation (−0·23, P=0·05) was observed between GH and INS, with the largest plasma INS levels in mid pregnancy (October 1·9 ng/ml), the lowest INS levels in December, 0·8 ng/ml and the largest serum GH concentration in December, 20·2 ng/ml. Results from the study indicate that DMI, MEI and MPI in grazing goats are useful indicators of the nutritive value of the forage consumed by goats which allowed them to keep an important steroidogenic luteal activity during gestation (P4=5·7±0·82 ng/ml, litter size=1·44 kids). Nonetheless, the observed plasma levels of glucose, urea, NEFA, INS and GH indicate that a schedule of energy supplementation may be outlined to ensure an adequate nutritional status of goats during late pregnancy and early lactation.