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ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Publications at this Location » Publication #73980
Title: CATTLE GRAZING PREFERENCE AMONG EIGHT ENDOPHYTE-FREE TALL FESCUE CULTIVARS

Author
item Shewmaker, Glenn
item Mayland, Henry
item Hansen, Susie

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Grass tetany is a nutritional deficiency of cattle and sheep caused by low magnesium concentrations in grass. Grass tetany, also called hypomagnesemia, in livestock grazing tall fescue causes and estimated $50 million annual loss to U.S. livestock producers. A breeding line of tall fescue, `HiMag', was selected for higher magnesium and calcium in the forage which should reduce the risk of grass tetany. It is estimated that HiMag could reduce grass tetany risk from tall fescue by 80%. This study showed that HiMag is consumed in amounts comparable to other tall fescue cultivars. HiMag should reduce grass tetany risk for the livestock producer.

Technical Abstract: `HiMag' tall fescue (Festuca arundinacea Schreb.) was selected for high Mg concentration to reduce grass tetany risk to ruminants, but neither animal preference nor consumption of HiMag were known. The objectives were to evaluate methods and to determine intake and preference by cattle for HiMag relative to 7 other tall fescues. The experimental design was a randomized complete block with 3 test-pastures (blocks), 3 replications nested within blocks, 8 cultivars (main plots), and 6 rows. Two groups of 6 Hereford heifers (Bos taurus L.) grazed the vegetative or boot-stage pastures for 48 h in May, June, August, and September of 1993 and 1994. Pre- and post-grazed forage was clipped and weighed to determine yield and utilization. Preference scoring of 0 to 10 (0 to 100% of forage eaten) was done by 4 trained observers at 24, 30, and 48 h. The heifers quickly learned to distinguish between cultivars, and their order of preference was Kenhy>KY 31>HiMag= Barcel =C1=Stargrazer>MO 96=Mozark. Their selection process fits the post-ingestive feedback theory of diet selection. The cultivar x trial(year) interaction (P=0.001) for preference indicates that cultivars respond differently to weather conditions which in turn affects animal preference. Preference scoring had high repeatability and ranked cultivars similar to the clip-weigh method. Preference scoring was accomplished with 27% of the experimental error and only 6% of the time required for clip-weigh. Only 61% of the variation in preference score (PS) was explained by the model: PS = 36 - 0.46(mg NDF/g) -1.66(mg P/g) -0.66 (Mg DM yield/ha). Dry matter intake of HiMag was 6.4 kg/AUD. Consumption and preference of HiMag by cattle are satisfactory relative to other tall fescues.