Abstract #T201

# T201
Impact of tannins and grazing schedule on nitrogen partitioning in lactating dairy cows.
C. A. Pozo*1, G. V. Kozloski1, C. Cajarville2, A. R. Sprunck2, Y. A. Ketenjian2, M. Cuffia3, J. L. Repetto2, 1Departamento de Zootecnia, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil, 2Facultad de Veterinaria, Universidad de la República, San José, Uruguay, 3Facultad de Agronomía, Universidad Nacional del Litoral, Esperanza, Santa Fe, Argentina.

The aim of this study was to evaluate the effect of dietary Acacia mearnsii tannin extract (TE) and managing the grazing schedule on N partitioning. The trial was conducted with 9 Holstein cows averaging 197 ± 12 d in milk, in a triplicate 3 × 3 Latin square design, through 3 22 d experimental periods. Cows were fed a ryegrass pasture (12.8% CP) and a total mixed ration (TMR, 16.4% CP). The 3 treatments consisted of morning grazing and afternoon TMR (AM), morning grazing and afternoon TMR added with 15 g/kg of TE (AMt), or morning TMR and afternoon grazing (PM). Individual dry matter intake was measured during 5 d of each period. Milk samples were collected during 2 d of each period for N analysis. Spot fecal and urine samples were collected twice daily during 3 d of each period. Fecal output was estimated using indigestible NDF as an internal marker. Urinary output was estimated assuming a daily creatinine excretion rate of 25.5 mg/kg of body weight. Statistical analysis was carried out using the PROC MIXED of SAS, where treatments were compared through contrast analysis. The treatments did not affect N intake or milk N excretion. Tannins did not affect fecal N excretion, but increased the fecal ADIN excretion (P < 0.01), and decreased total N and the urea-N excretion in urine (P < 0.05). Afternoon grazing increased fecal N excretion (P < 0.05), tended to decrease urinary total N excretion (P = 0.06) and decreased urinary N-urea excretion (P < 0.05). Although the treatments did not affect the total manure N excretion, the urinary N to fecal N ratio was reduced by 17 and 28% for AMt and PM respectively (P < 0.05). Results suggested that tannins inclusion in the TMR or afternoon grazing were effective to shift N excretion from urine to feces and to decrease the potential for ammonia emissions from manure of dairy cows. Table 1. Effect of tannin and grazing schedule on N utilization and manure excretion
Item, g/d Treatment SEM P-value
AM AMt PM AM vs AMt AM vs PM
N intake 465 467 459 22.2 0.94 0.42
Milk N 119 116 118 10.0 0.30 0.71
Fecal N 168 182 209 19.5 0.53 0.02
Fecal ADIN 7.1 17.6 10.0 1.20 <0.001 0.10
Urine N 214 196 197 16.5 0.04 0.06
Urine urea-N 123 105 106 18.7 0.02 0.03
Manure N 381 377 406 15.0 0.97 0.34
Urinary N:Fecal N 1.35 1.12 0.97 0.20 0.03 <0.001

Key Words: tannin, grazing schedule, nitrogen