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Title: INTAKE, DIGESTIBILITY, AND NITROGEN UTILIZATION OF ROBINIA PSEUDOACACIA FOLIAGE FED TO GROWING GOAT WETHERS

Author
item UNRUH-SNYDER, L - NORTH CAROLINA STATE UNIV
item LUGINGUHL, J - NORTH CAROLINA STATE UNIV
item MUELLER, J - NORTH CAROLINA STATE UNIV
item CONRAD, A - NORTH CAROLINA STATE UNIV
item Turner, Kenneth

Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2007
Publication Date: 7/20/2007
Citation: Unruh-Snyder, L.J., Luginguhl, J.M., Mueller, J.P., Conrad, A., Turner, K.E. 2007. Intake, Digestibility, and Nitrogen Utilization of Robinia Pseudoacacia Foliage Fed to Growing Goat Wethers. Small Ruminant Research. 71:179-193.

Interpretive Summary: Meat goats are an important livestock species due to the increased demand for chevon by many ethnic groups in the USA. Goats are browsers and prefer the weeds, woody shrubs and trees. Leguminous trees such as the black locust are indigenous to many of the goat production areas of the eastern USA. We evaluated intake, digestibility, and metabolic parameters by goats when black locust foliage used as a supplement to cool- and warm-season grass hay-based diets offered to growing meat goat kids. Black locust foliage supplement depressed hay intake, and overall digestibility of dry matter and fiber were reduced. Average daily gain was higher in diets containing black locust foliage compared to all hay diets. Black locust foliage could be used to maintain body condition of mature goats without detriment to weight gain over the summer as a substitute for expensive commercial supplementary feeds. This information is useful to scientists refining grazing management practices for silvopasture systems using meat goats, and to producers using goats to renovate woodlots and pasturelands. It will benefit small farm economy by reducing costs of purchased feed supplement for meat goats.

Technical Abstract: Black locust (BL; Robinia pseudoacacia L.), a native tree of southeastern USA known to contain substantial levels of condensed tannins (CT), was fed to 32, 4 month old (20.4 kg BW) Boer cross wether goats in two randomized complete block design trials. The objectives were to examine the effects of feeding hay diets containing several levels of fresh BL foliage on intake, digestibility, and N metabolism. First year (1999) diets were HE (100% Eastern gamagrass [EGH; Tripsacum dactyloides L.] hay), HEG (70% EGH and a 30% mixture of 59% ground corn [GC; Zea mays L.], 36% soybean meal [SBM; Glycine max L.], and 5% minerals), 25BL99 (75% EGH and 25% BL leaves), and 50BL99 (50% EGH and 50% BL leaves). Second year (2000) diets were HO (100% orchardgrass [OGH; Dactylis glomerata L.] hay), HOG (70% OGH and a 30% mixture of 63% GC, 37% SBM, and 5% minerals), 50BL00 (50% OGH and 50% BL leaves), and 75BL00 (25% OGH and 75% BL leaves). In 1999, apparent digestibilities of the diets in the order listed above were 62.4, 68.2, 58.0, and 60.6% (P = 0.001) for DM and 62.8, 72.5, 56.0, and 59.1% (P = 0.001) for crude protein (CP). Acid detergent lignin digestibilities were negative for diets 25BL99 ('56.7%) and 50BL99 ('49.3%), apparently due to the formation of insoluble tannin and lignin complexes during passage through the digestive tract. Intakes of DM were similar across diets. In 2000, apparent digestibilities of diet DM (64.4, 71.7, 64.8 and 65.4%) and CP (70.0, 76.0, 66.6, and 66.5%) did not differ. Lignin digestibilities were positive for diets 50BL00 (9.4%) and 75BL00 (29.6%) unlike those for year 1999. Overall, BL contained 10% CT and 18–34% hydrolyzable tannins. In 1999, N intake, urinary N (UN) excretion and N retained were higher for diet HEG (P = 0.01) than diet HE whereas fecal N excretion (FN) was similar for diets HEG, 25BL99 and 50BL99. In 1999, FN excretion as a percentage of N intake was higher (P < 0.02) in the BL diets, although UN as a percentage of N intake did not differ among diets. In 2000, N intake and FN output were higher for BL diets compared to diets HO (P = 0.01) and HOG (P = 0.02). Fecal N as a percentage of N intake was lower (P = 0.01) for diet HOG (24.0%) than for diets 50BL00 (33.4%) and 75BL00 (33.5%). Conversely, urinary N as a percentage of N intake was higher for diets HO and HOG compared to the BL diets (P = 0.02). Increased levels of dietary BL increased FN, suggesting that tannins formed insoluble protein complexes thus hindering digestibility.