Doctoral Dissertations

Date of Award

6-1975

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

K. M. Barth

Committee Members

H. A. Fribourg, S. L. Hansard, J. B. McLaren, J. H. Reynolds, J. R. Savage

Abstract

Midland bermudagrass pastures not fertilized with N (MID-1) or fertilized, in three equal installments, with either 112 CMID-2), 224 (MID-3) or 448 (MID-4) kg N/ha/year were compared to common bermudagrass (CB) fertilized with 112 kg N/ha/year and orchardgrass-ladino clover (OG) pastures. Forage constunption was determined by the cage-and-strip method from the middle of April to the middle of September during three consecutive years. Angus yearling steers, initially weighing about 215 kg, were used in a modified put-and-take grazing system. In vitro digestible dry matter (Tilley and Terry) and N (Auto-analyzer) were determined on all forage samples from the three years. During the last year, selected forage samples were analyzed for their amino acid content. In addition, jugular blood samples, obtained monthly from all tester animals, were analyzed for plasma urea nitrogen (PUN). The forage composition and intake data from the three years were reduced to polynomial equations describing the regression of in vitro digestible dry matter (IVDDM) and crude protein (CP) content and the intake of estimated total digestible nutrients (ETON) and CP on elapsed days of grazing (D). The results of these regression equations were used to generate predicted percentages of IVDDM, ETDN and CP and also of ETDN and CP intake per unit of metabolic weight and above maintenance for 20-day intervals until 140 elapsed days of grazing. Nitrogen fertilization increased the IVDDM of Midland bermuda-grass (45.6, 46.5, 47.4 and 48.5% for MID-1, MID-2, MID-3 and MID-4, respectively) but only MID-4 was significantly greater than MID-1. A decrease (P<.05) in IVDDM from April to September was observed in all treatments (50.8 to 37.7, 54.2 to 33.7, 56.6 to 34.2, 57.1 to 34.9, 49.8 to 40.2 and 69.2 to 58.3% for MID-1, MID-2, MID-2, MID-4, CB and OG, respectively). N fertilization increased CP<.05) the CP content of Midland pastures at all levels of fertilization (9.5, 10.7, 13.0 and 16.1% for MID-1, MID-2, MID-3 and MID-4, respectively). However, over the entire season, OG pastures contained more (P<.05) CP (17.7%) than all bermuda-grass forages. All forages decreased (P<.05) in CP content from April to September (14.3 to 7.5, 17.6 to 7.8, 18.2 to 10.1, 23.2 to 12.6, 17.2 to 7.9 and 19.1 to 16.2% for MID-1, MID-2, MID-3, MID-4, CB and OG, respectively). OG contained more (P<.05) ETDN in the consumed forage (61.7%) than the mean of all bermudagrasses (51.2%). The %ETDN in consumed forage decreased (P<.05) during the season in all treatments (62.3 to 45.8, 59.8 to 42.3, 61.6 to 43.6, 65.8 to 49.9, 57.2 to 48.6 and 67.6 to 57.8% for MID-1, MID-2, MID-3, MID-4, CB and OG, respectively). The mean CP content of consumed OG forage during the entire season was 19% compared to 15% for all bermudagrasses (P<.05). CB contained less (P<.05) CP on the average (13.4%) than the mean of all Midland forages (15.4%). MID-1 contained less (P<.05) CP (11.4%) than fertilized (MID-N) Midland (16.7%) but Midland fertilized with 224 and 448 kg N/ha (MID-HN) contained more (P<.05) CP (17.8%) in consumed forage than did MID-2. MID-4 contained 21.1% CP in consumed forage compared to 14.5% in MID-3 (P<.05). The CP content of consumed forage in all treatments decreased (P<.05) during the season (17.0 to 11.5, 17.3 to 12.0, 19.2 to 12.6, 30.2 to 17.3, 19.4 to 8.1 and 20.2 to 16.5% for MID-1, MID-2, MID-3, MID-4, CB and OG, respectively). Multiple regression equations were developed for the prediction of ADG from forage composition and consumption. All equations gave a more reliable prediction of ADG for steers grazing MID-N and CB pastures than for steers grazing MID-1 and OG pastures. Over the entire season, no significant difference was apparent between the mean PUN level of animals grazing OG (16.19 mg/100 ml) and that of animals grazing all bermudagrasses (14.41 mg/100 ml), nor did a significant difference exist between the PUN level of animals grazing CB (13.02 mg/100 ml) and that of animals grazing all Midland pastures (14.76 mg/100 ml). Animals grazing MID-1 had a lower (P<.OS) PUN level (11.57 mg/100 ml) than did animals grazing MID-N (15.82 mg/100 ml). Animals consuming MID-2 had a lower (P<.05) PUN level (13.97 mg/100 ml) than did animals grazing MID-HN (16.76 mg/100 ml). Animals consuming MID-3 had a lower (P<.G5) PUN (14.34 mg/100 ml) than did animals grazing MID-4 (19.18 mg/100 ml). Regression equations were developed to predict ADG, % CP in consumed forage, %DDM content of consumed forage and CP intake per unit of metabolic weight from PUN levels. The general order of amino acid levels, from high to low, expressed as a percentage of forage CP was aspartic acid, alanine, glutamic acid, valine, phenylalanine, arginine, lysine, leucine, glycine, isoleucine, threonine, tryosine, serine, proline, histidine and methionine. The mean of MID-1 and MID-4 contained more (P<.05) serine, lysine, aspartic acid, glutamic acid and glycine than did OG. The latter contained more (P<.05) methionine than the mean of MID-1 and MID-4. MID-1 contained significantly more arginine, threonine, serine, glycine and valine than did MID-4. The latter contained a higher per-centage of methionine (P<.05) than did MID-1.

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