HISTIDINE DOSE-RESPONSE EFFECTS ON LACTATIONAL PERFORMANCE AND PLASMA AMINO ACID CONCENTRATIONS IN LACTATING DAIRY COWS: 1. METABOLIZABLE PROTEIN-ADEQUATE DIET
The objective of this experiment was to determine the effect of increasing digestible (d)His doses on milk production, milk composition and plasma AA concentrations in lactating dairy cows fed diets that meet or exceed their energy and metabolizable protein (MP) requirements. In a companion paper (Räisänen et al., 2021) results are presented on the effect of increasing dHis dose with a MP-deficient basal diet. In this experiment, 16 Holstein cows (72 ± 15 days in milk) were used in a replicated 4 × 4 Latin square design experiment with 4, 28-d periods. Treatments were: (1) control, total mixed ration (TMR) with 1.8% dHis of MP (TMR1; dHis1.8), (2) a different TMR with 2.2% dHis (TMR2; dHis2.2), (3) TMR2 supplemented with rumen-protected (RP)His to supply 2.6% dHis (dHis2.6), and (4) TMR2 supplemented with RPHis to supply 3.0% dHis of MP (dHis3.0). Estimated dHis intakes calculated at the end of the experiment were 46, 58, 69 and 79 g/d for dHis1.8, dHis2.2, dHis2.6 and dHis3.0, respectively. Contrasts were used to compare TMR1 with TMR2 and to test the linear and quadratic effects of RPHis inclusion rate on TMR2. There were no effects of TMR or dHis dose on dry matter intake or MY, while energy-corrected milk (ECM) yield was quadratically increased, being greatest for cows on treatment dHis2.6. Milk true protein and lactose concentrations and milk true protein yield were not affected by TMR or dHis dose. Milk fat concentration and yield increased quadratically, and lactose yield tended to increase quadratically with increasing dHis dose. Calculated apparent efficiency of His utilization (EffHis) decreased quadratically with increasing dHis supply. Further, plasma concentration of His was greater for cows on TMR2 compared with TMR1. When a MP-adequate diet was fed to dairy cows, milk true protein concentration and yield were not affected by dHis supply, but milk fat and ECM yields of dairy cows were optimized at dHis supply of 69 g/d or 2.65% of MP.
|Work Title||HISTIDINE DOSE-RESPONSE EFFECTS ON LACTATIONAL PERFORMANCE AND PLASMA AMINO ACID CONCENTRATIONS IN LACTATING DAIRY COWS: 1. METABOLIZABLE PROTEIN-ADEQUATE DIET|
|License||CC BY-NC-ND 4.0 (Attribution-NonCommercial-NoDerivatives)|
|Publisher Identifier (DOI)||
|Deposited||November 19, 2021|
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