Pozo Claudio A, Kozloski Gilberto V, Cuffia Maira, Repetto José L, Cajarville Cecilia
Departamento de Zootecnia, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
Departamento de Producción Animal, Facultad de Ciencias Agrarias, Universidad Nacional del Litoral, Esperanza, 3080, Argentina.
J Dairy Sci. 2022 Jun;105(6):4987-5003. doi: 10.3168/jds.2021-21149. Epub 2022 Apr 18.
Our aim was to evaluate whether increasing soluble carbohydrates in the herbage by changing the time of the grazing session or including Acacia mearnsii tannin in the diet would affect intake, digestion, N partitioning, and productive performance of dairy cows fed a diet combining ryegrass herbage with partial total mixed ration (PMR). We hypothesized that both strategies could reduce the concentration of NH-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 PMR [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 PMR meal (AM); (2) morning PMR meal and afternoon grazing session (PM); and (3) morning grazing session and afternoon PMR meal supplemented with 15.0 g of tannins/kg of PMR 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 16:1 cis-9 and Δ-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 herbage DMI and reduce dry matter and crude protein digestibilities. Treatments did not affect cow eating and ruminating behavior except for the proportion of time spent eating PMR, 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 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 PMR and ryegrass herbage.
我们的目的是评估通过改变放牧时间或在日粮中添加黑荆树单宁来增加牧草中可溶性碳水化合物的含量，是否会影响以黑麦草和部分全混合日粮（PMR）组合为食的奶牛的采食量、消化率、氮分配和生产性能。我们假设这两种策略都可以降低瘤胃中NH-N的浓度，减少尿氮排泄。九头荷斯坦奶牛用于重复的3×3拉丁方实验，有3个为期22天的实验期。奶牛每天固定采食一定量的PMR[占预测个体干物质采食量（DMI）的60%]，并在每天5小时的1次放牧中自由采食牧草。处理方式为：（1）上午放牧，下午采食PMR日粮（AM）；（2）上午采食PMR日粮，下午放牧（PM）；（3）上午放牧，下午采食添加了15.0克单宁/千克PMR干物质的PMR日粮（TAN）。产奶量不受处理方式的影响。尽管TAN组的蛋白质浓度低于PM组，但各处理间任何成分的产量均未检测到差异。除16:1顺-9以及Δ-去饱和酶比率14:1/14:0和16:1/16:0外，牛奶脂肪中单个或分组脂肪酸的浓度不受处理方式的影响，TAN组的这几个指标较低。处理方式不影响总DMI，但PM组倾向于增加牧草DMI并降低干物质和粗蛋白消化率。处理方式不影响奶牛的采食和反刍行为，除了采食PMR所花费的时间比例，PM组和TAN组的该比例较高。尽管未检测到处理方式对瘤胃发酵、尿中嘌呤衍生物排泄或乳中氮排泄有相关影响，但与AM组相比，PM组和TAN组均使尿中总氮排泄量平均降低了8%。总之，将放牧时间从上午改为下午以及在日粮中添加单宁可有效减少尿氮排泄，但不会改变采食PMR和黑麦草的奶牛的生产性能。
