Intake, digestibility, rumen fermentation and nitrogen balance in sheep offered alfalfa silage with different proportions of the tannin-rich legume sericea lespedeza

Abstract

Dietary manipulations to include tannins can change the proportion and amounts of nitrogen (N) excreted in the urine and feces as well as improve nitrogen use efficiency by ruminants. This study was conducted to investigate the effects of adding different proportions of sericea lespedeza (Lespedeza cuneate) hay (SL) containing tannins (16.8% total condensed tannins; CT) to alfalfa (Medicago sativa) silage. Alfalfa silage was either offered alone (0 g/kg; CONT) or mixed with chopped SL to provide 90 (LOW), 180 (MED), or 270 g/kg SL (HIGH) or 15, 30, or 45 g CT/kg on a dry matter (DM) basis. These diets were offered randomly for ad libitum consumption to 16 Dorper ewe lambs (42.1 ± 1.15 kg BW; Period 1; 41.7 ± 1.12 kg BW; Period 2) in a randomized complete block design experiment where each treatment was offered to four lambs during each of two periods. The same 16 lambs were used in both periods, resulting in eight total observations/treatment. Each period consisted of a 14-d dietary adaptation period followed by 5 d of total fecal and urine collection. Data were analyzed using PROC MIXED of SAS. Dry matter (DM), organic matter (OM), neutral detergent fiber (aNDF) and acid detergent fiber (ADF) digestibility as well as digestible DM and OM intake (g/day or g/kg BW) decreased linearly (P < 0.05) with increasing SL in the diet. Ruminal acetate and butyrate molar proportions increased quadratically (P = 0.01), whereas ruminal isobutyrate and isovalerate decreased linearly (P = 0.02) with increasing SL in the diet. Apparent N absorption (g/kg N intake) decreased linearly (P < 0.05) with increasing SL in the diet. Urinary N excretions (g/kg N intake) tended (P = 0.10) to respond quadratically while fecal N (g/kg N intake) increased linearly (P < 0.01) with increasing SL proportion in the diet. In this study, supplementation with sericea lespedeza as a tannin source to alfalfa silage decreased forage digestibility without affecting feed intake, and significantly increased N excreted in feces and tended to decrease urine N excretion without affecting N balance. Therefore, feeding tannins in diet can alter N excretion route from urine to feces but may not improve N-use efficiency by the animal.