Study On The Effect Of Synchronization Of Dietary Carbohydrate And Protein Supply And Dietary Protein And Energy Levels On The Use Efficiency Of Nitrogen In Holstein Dairy Cows

Improving the use efficiency of dietary nitrogen, which is low for ruminants, is a hotspot for current study. The objective of the current series of experiments was to asses the effect of dietary synchrony of OM and N supply to rumen and dietary CP and energy level on the metabolism and performance of Helstein dairy cows to evalue the use efficiency of dietary N. The whole study has two parts: Part 1, The effects of ruminal synchronization of dietary energy and nitrogen release on the productivity, ruminal fermentation, and nitrogen balance in lactating Holstein cows. Part 2, Effects of varying dietary protein and energy levels on production of lactating dairy cows.Experiment 1. This experiment was conducted to study the effects of synchrony of diets on rumen fermentation, performance and N balance. A 4×4 Latin square design was used. Four Holstein cows in mid-lactation were equipped with ruminal cannulas and fed with four synchronized diets ( diet I,SI=0.95, diet II,SI=0.90, diet III,SI=0.83, diet IV,SI=0.77 ). Different diets content similar CP and energy. Each experimental period lasted for 21 d and measurements occurred during last 6 d of each period, total feces and urine was collected to evaluate the total-tract apparent digestibility and N losses. Rumen pH was decrease as synchrony of diet increased(P<0.05),cocentrations of acetate, propionate and butyrate and total-volatile fatty acid and NH3-N, and also ruminal volume and liquid dillution rates and microbial N outflow didi no differ(P >0.05). Milk yield and yield of milk protein and lactose trend to be higher when synchrony of diet was higher ( P<0.05), milk composition including fat protein and lactose and milk urea N was similar for cows fed with different diets, Both significant result may come from the difference of concentrate in four diets. Milk N and fecal N loss were increased when synchrony increased (P<0.05) No significant difference was detected on urinary N, although it increased as synchrony of diet increased(P<0.05). Synchrony of diet also had no effect on efficiency of N intake used for milk N, total-tract apparent digestibility and total N loss. The result indicated that synchrony diet had effect of improving microbial protein synthesis and increasing the production of milk protein.Experiment 2. This experiment was conducted to study the effects of varying dietary protein and energy levels on production of lactating dairy cows. Four mulitiparous and mild-lactation Holstein dairy cows were randomly assigned to a 4×4 Latin square design with a 2×2 factorial arrangement of treatments to evalue two nenergy levels with two CP levels on milk production and N banlance. Also, total feces and urine was collected to evaluate the total-tract apparent digestibility and N losses. When CP increased from 14.1% to 18.2%, DMI was greater(0.050.1). The effect of interaction of dietary energy and protein on milk protein was conducted(0.050.1), but urea N loss increased by increasing dietary CP level P<0.05. The result indicated when NEL met 1.52-1.78Mcal/kg DM, a 14.1% of dietary CP level appeard sufficient for cows producing 27.0-30.2kg/d of milk in this study. Lower dietary CP can decrease excretion of enviromentally labile urinary N.