| The purpose of this study was to investigate the effects of dietary N-carbamoyl glutamic acid?NCG?levels on performance,digestion,metabolism,rumen fermentation and blood biochemical parameters of lactating cows.Forty-eight healthy Holstein dairy cows with similar parity,days in milk?DIM?,milk yield and body condition were selected and randomly divided into groups ?,?,? and ? with 12 replicates in each group and 1cow in each replicate.The dairy cows in groups ?,?,? and ? were fed 0 g,15 g,20 g and25 g NCG respectively daily,and each group was fed the same basic diet.The experimental period was 60 days.The results are as follows:1)The 4%fat corrected milk?FCM?of of group ?,? and ? increased by7.29%,6.33%and 3.54%respectively compared with group ??P<0.01?.The milk yield of group ?,? and ? was 4.75%,5.28%and 4.35%higher than that of group I?P<0.01?.The milk protein rate of group ? was 7.36%higher than that of group ??P<0.01?.There was an increasing trend for milk protein rate in group ? and group ? compared with group I.The number of somatic cells in group ?,? and ? was lower than that in group ?,which was decreased by 16.56%,28.17%?P<0.05?and 21.51%,respectively.Compared with group ?,the urea nitrogen in milk of group ?,? and ? decreased by 17.73%,13.46%and 16.31%?P<0.01?.There was no significant difference in feed conversion ratio?FCR?between groups ?,?,? and ??P>0.05?.2)Urine nitrogen excretion was higher in group ? and group ?,and lowest in group ??P<0.01?.The milk nitrogen of group ?,? and ? were higher than those of group ?,and increased by 33.37%?P<0.01?,6.10%?P>0.05?and 6.10%?P>0.05?,respectively.The milk nitrogen of group ? were significantly higher than those of other groups?P<0.01?.The nitrogen conversion rates in group ?,? and ? were higher than those in group ?,which increased by 27.77%,2.80%and 5.98%,respectively,and the conversion rates in group ? were significantly higher than those in other groups?P<0.01?.3)The concentrations of ammonia nitrogen?NH3-N?in the rumen fluid of the group ?,? and ? were significantly lower than those in the group ?,which decreased by9.94%?P>0.05?,20.57%?P<0.05?and 14.68%,respectively.?P>0.05?,wherein the lowest concentration of NH3-N in group ? was 10.39 mg/dL.The concentration of rumen microbial crude protein?MCP?in group ?,? and ? was 13.79%?P>0.05?,29.31%?P<0.01?and 7.76%?P>0.05?higher than that in group ?,with the highest concentration of MCP in group ? being 1.50 mg/mL.The concentration of acetic acid in group ?,? and ? was higher than that in group ?.The concentration of acetic acid in group ? was significantly higher than that in group ? and ??P<0.01?.The concentration of propionic acid in each group was significantly different?P<0.01?,with the lowest in group ? and the highest in group ?.The acetic acid/propionic acid ratio in group ?,? and ? was 6.69%?P>0.05?,18.83%?P<0.01?and 10.88%?P<0.05?lower than that in group ?,respectively.The total volatile fatty acids?T-VFA?in group ?,? and ? were higher than those in group ?,which increased by 22.50%?P<0.01?,38.39%?P<0.01?and11.94%?P<0.05?,respectively.4)The serum glucose?GLU?of group ?,? and ? was significantly higher than that of the ? group?P<0.01?,which increased by 14.35%,19.34%and 18.63%,respectively.The serum urea nitrogen?BUN?of the test group ?,? and ? decreased compared with the ? group,which decreased by 16.36%?P<0.01?,10.63%,13.50%?P<0.05?.The blood ammonia concentration in group ?,? and ? were lower than the ? group?P<0.05?,which decreased by 33.51%?P<0.01?,25.78%?P<0.05?and 27.83%?P<0.05?,respectively.The plasma amino acid?AA?concentration in group ? was significantly higher than that in the other groups?P<0.01?,and there was no significant difference between the groups ?,? and ?.5)The total antioxidant capacity?T-AOC?of group ?,? and ? was significantly higher than that of the ? group?P<0.01?,which increased by 28.09%,33.25%and41.80%.The superoxide dismutase?SOD?of each group showed an upward trend,and SOD in group ?,? and ? were significantly higher than those in group ??P<0.01?,which increased by 31.83%,44.74%and 52.85%,respectively.There was no significant difference in glutathione peroxidase?GSH-Px?between group ? and group ?,but there was significant difference between group ? and group ??P<0.01?.Compared with group ?,group ?,group ? and group ? increased by 10.50%,32.53%and 37.32%respectively.The concentrations of malondialdehyde?MDA?in groups ?,? and ? were significantly lower than those in group I?P<0.01?,which decreased by12%,18.18%and 44.85%,respectively.6)Serum immunoglobulin A?IgA?in groups ?,? and ? was significantly higher than that in group ??P<0.01?,which increased by 16.50%,88.04%and73.66%,respectively.Immunoglobulin M?IgM?in group ? was significantly higher than that in group ?,?,and ??P<0.01?,and there was no significant difference between groups ?,?,and ??P>0.05?.Immunoglobulin G?IgG?in groups ?,? and ? was significantly higher than that in group ??P<0.01?,which increased by 13.71%,29.99%and20.17%,respectively.7)Serum cortisol in group ?,? and ? was significantly lower than that of group ??P<0.01?,which decreased by 19.45%,42.13%and 37.29%.The levels of triiodothyronine?T3?in group ?,? and ? were significantly higher than those in group I?P<0.01?.The growth hormone?GH?in group ?,? and ? was significantly higher than that in group ??P<0.01?,which was increased by 38.23%,55.58%and 38.11%,respectively.Prolactin?PRL?in groups ?,? and ? was significantly higher than that in group ??P<0.01?,which increased by 32.39%,34.66%and 42.29%,respectively.The superoxide diamutase in groups ?,? and ? were significantly higher than those in group ??P<0.01?,which increased by 16.94%,38.70%and 45.35%,respectively.The plasma heat shock protein-70?HSP-70?in the test group ? was significantly higher than that in group ? and ??P<0.01?.Ascorbic acid?AC?in groups ?,? and ? was significantly higher than those in group ??P<0.01?,which increased by 12.00%,31.89%and 35.73%,respectively.To sum up,under the conditions of this experiment,adding NCG can increase the milk yield and milk protein,reduce nitrogen emissions,promote rumen fermentation of dairy cows,and alleviate the adverse effects of heat stress on dairy cows.The most suitable addition amount of NCG is 15 g-20 g per cow per day. |
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