Effects of tannins and grazing schedule on nitrogen use efficiency and digestibility in lactating dairy cows

ANDRIELE Z. KÜLZER; GILBERTO V. KOZLOSKI; CECILIA CAJARVILLE; CLAUDIO A. POZO

Foz do Iguaçu

Congreso; 54 Annual Meeting of the Brazilian Society of Animal Science; 2017

Sociedade Brasileira de Zootecnia

Tannins and managing grazing schedule are potential strategies to improve the nitrogen use efficiency. However, few information of the impact of this strategies in dairy cows consuming mixed diets combining total mixed rations with pasture are available. Nine Holstein cows averaging 197 ± 12 days in milk were used in a triplicate 3 x 3 Latin square trial, conducted through three experimental periods of 22 days, to evaluate the effect of dietary Acacia mearnsii tannin extract (TE) and the grazing schedule on N use efficiency (NUE) and digestibility. Cows were fed a ryegrass pasture (12.8% CP) and a total mixed ration (TMR, 16.4% CP). The three treatments consisted of: morning grazing and afternoon TMR without TE (AM), morning grazing and afternoon TMR added with 15 g kg-1 of TE (AMt), or morning TMR without TE and afternoon grazing (PM). Individual dry matter intake was measured during five days of each period. Milksamples were collected during two days of each period for N analysis. Spot fecal samples were collected twice a day during three days of each period. Fecal output was estimated using indigestible NDF as an internal marker. Apparent digestibility was calculated as: ((N intake ? N fecal) N intake-1) x 100. Statistical analysis was carried out using the MIXED procedure of SAS, where treatments were compared through contrast analysis. The contrasts tested were: AM vs. AMt and AM vs. PM. The treatments did not affect N intake (464 g d-1), milk N excretion (118 g d-1), or NUE for milk production (25.5%). Compared to AM, tannins did not affect fecal dry matter (DM) output (7.0 kg d-1), fecal N excretion (182 g d-1), or N digestibility (60.7%). When compared with AM, afternoon grazing increase (P