1547
Effects of Supplementing Limiting Amino Acids in Diets with Reduced CP on Nitrogen Excretion
Lowering dietary CP content while supplementing limiting essential amino acids (EAA) has potential to increase N efficiency and decrease N excretion. Ten Holstein cows were blocked by DIM into two 5x5 Latin squares with 5 treatments: (1) positive control (16% CP); 14.9% CP with (2) or without (3) EAA infusion; or 13.5% CP diet with (4) or without (5) EAA infusion. Diets contained alfalfa silage, corn silage, high moisture corn, canola meal, soybean meal and soybean hulls. The infusion solutions were prepared according to AminoCow to provide all limiting EAA and infused continuously into cows' abomasum. Amounts of Met, Lys, His, Leu and Val were, respectively, 11, 11, 5, 5, and 0 g/d for treatment 2 and 15, 27, 11, 22, and 6 g/d for treatment 4. Data from the last 4 d of each 14-d period were analyzed using Proc Mixed. Dry matter intake was not different among treatments (P > 0.10) and was highly variable. Therefore, DMI was included in the model to isolate treatment effects. Significance was declared at P < 0.10. Contrasts and LS-means are reported. There was no difference among treatments for fecal N excretion. Increasing CP level increased urinary N content and proportion of urea in total urinary N. The EAA infusion on 14.9% CP increased urinary N excretion relative to the same diet without infusion. However, when infused on the 13.5% CP diet, EAA decreased urinary N excretion relative to the same diet without infusion. This suggested that the 14.9% CP diet provided sufficient EAA for milk protein synthesis, while the 13.5% CP diet was EAA deficient and supplementation improved N utilization.
|
Treatments |
Contrasts1 |
|||||||
Variable |
16% CP |
14.9% CP +EAA |
14.9% CP |
13.5% CP +EAA |
13.5% CP |
1 |
2 |
3 |
4 |
Urinary N, % |
0.15 |
0.12 |
0.12 |
0.11 |
0.11 |
<0.001 |
<0.001 |
>0.10 |
>0.10 |
Urinary N excretion, g/d |
111 |
113 |
99 |
86 |
100 |
>0.10 |
>0.10 |
0.089 |
0.076 |
Urine N/N intake, % |
18.6 |
20.7 |
18.0 |
16.7 |
20.1 |
>0.10 |
>0.10 |
0.072 |
0.024 |
Urea N/total urinary N, % |
91 |
80 |
77 |
74 |
73 |
0.005 |
<0.001 |
>0.10 |
>0.10 |
Fecal N, % |
2.92 |
2.88 |
2.84 |
2.73 |
2.86 |
>0.10 |
>0.10 |
>0.10 |
>0.10 |
Fecal N excretion, g/d |
199 |
191 |
196 |
172 |
187 |
>0.10 |
>0.10 |
>0.10 |
>0.10 |
Feces N/N intake, % |
34 |
35 |
35 |
34 |
36 |
>0.10 |
>0.10 |
>0.10 |
>0.10 |
1Contrasts: 1=16 vs 14.9; 2=16 vs 13.5; 3=14.9 vs 14.9+EAA; 4=13.5 vs13.5+EAA
Keywords: Amino acid infusion, nitrogen excretion, protein