Effects of tarbush ingestion on intake, digesta kinetics, in situ digestion, ruminal fermentation, and nitrogen balance of sheep consuming low quality tobosa grass diets

TitleEffects of tarbush ingestion on intake, digesta kinetics, in situ digestion, ruminal fermentation, and nitrogen balance of sheep consuming low quality tobosa grass diets
Publication TypeConference Paper
Year of Publication1995
AuthorsKing D., Estell RE, Fredrickson E.L., Havstad K, Wallace J.D., Murray L.W.
Conference NameJournal of Animal Science
Date Published1995
Keywordsintake, nitrogen balance, rumen ammonia, sheep, tarbush ingestion, tobosa grass
AbstractTarbush (Flourensiacernua) represents a substantial biomass in the Chihuahuan Desert. Two studies were conducted to assess intake, in situ digestion, passage rate, ruminal fermentation, and nitrogen balance of sheep fed a low quality tobosa (Hilariamutica) diet containing up to 30% tarbush leaves. Tarbush was harvested and air dried, and leaves were separated from stems. In Exp. 1, 16 ruminally cannulated Polypay x Rambouillet lambs (avg BW = 46 kg) were individually fed (twice daily) ground (2.54 cm) tobosa (5.9% CP, 80% NDF; DM basis) substitued with 0, 10, 20, or 30% (DM basis) tarbush (18.9% CP, 33% NDF) leaves ad libitum for 28d. In Exp. 2, 24 Polypay x Rambouillet wethers (avg BW = 47 kg) in metabolism crates were allotted to one of the four treatments described above (n = 5) or 26% ground alfalfa (n = 4). Sheep were fed ad libitum for 11 d and then restricted to 1% of BW for 11 d to equalize intake. In Exp. 1, DMI for 20 and 30% tarbush treatments was greater (P = .0049) during week 3 than 0 and 10% treatments. Molar butyrate proportions (P = .0032) and total VFA concentrations (P = .0064) were greater for the 30% tarbush treatment than other treatments. Sheep fed 30% tarbush had greater (P < .0046) ruminal ammonia concentrations than sheep fed other diets at 6, 8, and 12 h postfeeding. In Exp. 2, all treatments resulted in similar but negative N retentions (-2.4, -2.2, -2.8, -2.0, and -1.5 g/d for sheep consuming 0, 10, 20, or 30% tarbush or alfalfa, respectively). Because only 30% tarbush elicited measurable responses in Exp. 1 (based on ruminal ammonia dn total VFA concentrations), nutrients contained by tarbush (especially CP) did not appear to be completely available to sheep. Low DMI observed in Exp. 2 was likely due to secondary compounds in tarbush and may partly explain why no differences in N balance were observed in Exp. 2.