| This thesis will study the potential of N and P emissions from lactating Holstein dairy cows through the following two tests.Experiment 1:In order to control emissions of nitrogen and phosphorus in feces and urine of dairy cows without effects on production performance,this study investigate the effects of reduction of dietary nitrogen and phosphorus or using compound additives on production performance,blood biochemical parameters,and nitrogen and phosphorus emissions of lactating Holstein cows.Thirty-six lactating Holstein cows were randomly selected and divided into 3 groups with 12 cows per group.Cows in control group(CR)were fed the original diet in farm,those in low protein and phosphorus group(LPP)were fed an experimental diet which had 0.70%and 0.03%lower protein and phosphorus than the original diet in farm,and those in compound additive group(CA)were fed the original diet in farm and compound additives(composed of active yeast,enzyme preparation and organic zinc).The per-test lasted for 7 d,and the formal test lasted for 30 d.The results showed as follows:there were no significant differences of milk yield,dry matter intake and milk composition(P>0.05);compared with CR group,apparent digestibility of acid detergent fiber and phosphorus were increased by 73.12%and 42.94%(P<0.05),respectively;compared with CR group,emissions of total nitrogen and total phosphorus in LPP group were decreased by 9.11%and 26.34%(P<0.05),respectively,and those in CA group were decreased by 16.35%and 16.10%(P<0.05),respectively;blood aspartate aminotransferase(ALT)activity and phosphorus content in CA group were significantly higher than those in CR group(P<0.05),while blood biochemical parameters in CR group and LPP group were not significantly different(P>0.05).Under the condition of normal nutritional requirements are satisfied,appropriately controlling nitrogen and phosphorus intakes of cows,or using the compound additives can reduce the emission of nitrogen and phosphorus.Experiment 2:In order to control emissions of nitrogen and phosphorus in feces and urine of dairy cows without effects on production performance,this study was to investigate the effects of low-protein amino acid balanced diets on performance and nitrogen emissions of dairy cows.Thirty Holstein cows were randomly selected and divided into 3 groups(n=10):control group(fed basal diet),Group Ⅰ and Ⅱ reduced 0.80%and 1.66%of nitrogen(crude protein)on the basis of the control group,and then added RPLys and RPMet to balance the amino acids in the diet.The trial lasted 49 days:7days of feeding adaptation period and 42 days of the experimental period.The results showed that,compared with the control group,there were no significant effects on the feed intake of the Group Ⅰ and Ⅱ,the standard milk yield of 4%and the milk composition(P>0.05),and the apparent digestibility of the diet also had no significant effect(P>0.05).When compared with the control group,the total nitrogen excretion in Group Ⅰ Ⅱ were decreased by 7.67%and 15.19%(P<0.05),respectively.Furthermore,the economic benefits were increased by 0.45 and 3.17 yuan/(head·day)respectively compared with the control group.These above results show that the appropriate reduction of nitrogen levels in the diet on the basis of amino acid balance does not affect the performance of dairy cows,but also reduces the environmental pollution caused by nitrogen excretion and provides basis for the practical application of low-protein amino acid balanced diets. |
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