Changing the grazing session from morning to afternoon or including tannins in the diet was effective in decreasing the urinary nitrogen of dairy cows fed a total mixed ration and herbage

CLAUDIO A. POZO; GILBERTO V. KOZLOSKI; MAIRA CUFFIA; JOSE L. REPETTO; CECILIA CAJARVILLE

JOURNAL OF DAIRY SCIENCE

AMER DAIRY SCIENCE ASSOC-ADSA

Año: 2022

0022-0302

Our aim was to evaluate whether increasing soluble carbohydrates in herbage by changing the time of the grazing session or including in the diet Acacia mearnsii tannin would impact intake, digestion, N partitioning and productive performance of dairy cows fed a diet combining ryegrass herbage with partial total mixed ration (pTMR). We hypothesized that both strategies could reduce the concentration of NH3-N in the rumen, reducing urinary N excretion. Nine Holstein cows were used in a triplicate 3 × 3 Latin square experiment with 3 experimental periods of 22 d. The cows were fed a fixed amount of pTMR (60% of the predicted individual dry matter intake (DMI)), and an unrestricted amount of herbage in 1 grazing session of 5 h/d. The treatments were: 1) morning grazing session and afternoon pTMR meal (AM), 2) morning pTMR meal and afternoon grazing session (PM), and 3) morning grazing session and afternoon pTMR meal supplemented with 15.0 g tannins/kg pTMR dry matter (TAN). Milk production was not affected by treatments. Although the protein concentration was lower for TAN than for PM, no differences were detected for the yield of any component between treatments. The concentration of individual or grouped fatty acids in milk fat was not affected by treatments, except for the 16:1 cis-9, and ∆9-desaturase ratios 14:1/14:0 and 16:1/16:0, which were lower for TAN. Treatments did not affect total DMI, but PM tended to increase the herbage DMI and reduce dry matter and crude protein digestibilities. Treatments did not affect cow eating and ruminating behavior except for the proportion of the time spent eating pTMR, which was higher for PM and TAN. Although no relevant effects of treatments on ruminal fermentation, purine derivatives excretion in urine, or N excretion in milk were detected, both PM and TAN decreased the total N excreted in urine by an average of 8% compared with AM. In conclusion, changing the grazing session from the morning to the afternoon period of the day and including tannins in the diet were effective in decreasing the excretion of urinary N but did not change the productive performance of dairy cows fed pTMR and ryegrass herbage.