Nutrition of goats grazing sand shinnery oak (Quercus havardii) ranges in West Texas

Abstract

The objectives of this study were: 1) compare botanical diet composition, diet quality, and forage intake of Angora and Spanish goats foraging sand shinnery oak (oak) during the summer of 1986 in west Texas, 2) monitor blood levels of tannic acid equivalent (TAE) and urea nitrogen (BUN) in goats grazing oak range, 3) determine digestibility and nitrogen balance as a function of different levels of oak in the diet, and 4) determine the effect of oak resin and phenol fractions on deterring consumption. Esophageally-fistulated wether goats were used. Intake was estimated using the total fecal output: indigestibility ratio. Spanish goats selected (P>0.05) more oak and forbs, and less grasses than Angora goats. Goats increased (P<0.05) oak consumption from June (31%) to August (55%), but decreased (P<0.05) dietary forbs from 23 to 5%. Condensed tannins in oak was 35.9 mg/g throughout the study. TAE was higher (P>0.05) in Spanish (1.6 ug/mi) than in Angora goats (0.8 ug/ml), and declined (P>0.05) as the summer progressed. TAE was not detected in blood serum of goats in the metabolism trials. Dietary digestibility was similar between breeds, and it declined (P<0.05) as the season progressed. Dietary crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and lignin levels were similar between breeds, and remained constant throughout the study. BUN was not different between breeds, increased (P>0.05) as the summer advanced, but decreased (P<0.05) with increased oak levels in the rations. Organic matter intake (OMI) increased (P<0.05) as the season progressed. OMI was 0.9, 1.2, and 1.4% of body weight for Angora, and 0.9, 1.5, and 1.8% for Spanish goats in June, July, and August, respectively. Apparent digestibility of organic matter, CP, NDF, and ADF decreased (P<0.05) as oak levels increased in the rations. With increased dietary oak levels, fecal nitrogen increased (P<0.05) and urinary nitrogen decreased (P<0.05). Also, digestible and retained nitrogen declined (P<0.05) with increased levels of dietary oak. Relative consumption of alfalfa pellets was not affected when treated with ether extract compounds of oak. Goats ate less alfalfa pellets treated with methanol (P<0.10) than untreated pellets.