The Effect Of Abomasal Infusion Of Histidine And Proline On Milk Composition And Mammary Amino Acid Utilization In High Producing Lactating Dairy Cows

The high cost of feed and increasing necessity to reduce nitrogen (N) waste in dairy production systems has driven research in the area of improving milk protein synthesis and overall efficiency of N utilization in lactating dairy cows. One strategy that has been investigated is reducing the total crude protein (CP) level of the diet while supplementing the ration with limiting amino acids (AA) for milk production. However, currently there is not enough information on the effects of increasing absorptive supply of certain individual AA on productive performance and mammary metabolism in high producing lactating dairy cows. Specifically, histidine (His) has been shown to be a limiting amino acid in grass fed lactating dairy cows and to alter fat secretion under certain conditions. In one published study in which the nonessential AA proline (Pro) was infused into the duodenum of two cows, a significant increase in milk protein output and a reduction in arginine (Arg) uptake by the mammary gland were observed. The objective of this study was to determine the effect of abomasal infusion of His and Pro, separately and in combination, on productive performance and mammary amino acid utilization in high producing lactating dairy cows. Four rumen-fistulated Holstein cows (52 ± 16 DIM) with indwelling intercostal arterial catheters were used in a 4 × 4 Latin square experiment. Experimental treatments were continuous abomasal infusion of water (Control), His (H, 10g/d), Pro (P, 20 g/d), and His (10 g/d) + Pro (20 g/d)(H+P), with 7-d treatment periods. Cows were fed a TMR (15.6 % CP, 2.7 Mcals/kg ME) once per day for ad libitum intake, and refusals were measured and analyzed. The CNCPS v6.1 was used to formulate a diet to exceed the metabolizable energy requirement, provide 95% of the predicted metabolizable protein requirement, and supply adequate amounts of all essential amino acids, except Arg. Compared to the Control treatment, abomasal infusion of Pro decreased dry matter intake (DMI) by 1.8 kg/d and improved feed efficiency (P ≤ 0.05) by 0.16 kg 3.5% FCM per kg dry matter. Fat corrected milk (FCM) yields were not affected by treatment (51.8 kg/d, TRT C; 50.6 kg/d, TRT H; 49.0 kg/d TRT H+P; 52.4 kg/d TRT P). Abomasal infusion of His resulted in no difference in milk yield or composition, and there was no effect of Pro infusion on protein and fat contents and yields. Pro infusion increased lactose percentage (P ≤ 0.05) but not yield. The lactose response suggests that longer infusions might have resulted in increased milk yield. Mammary blood flow, expressed as L plasma/L milk, was not significantly different among treatments; though, Pro infusion increased blood flow by 14% relative to the control treatment (694.8 vs. 606.8 L plasma/L milk for P and C, respectively). Arterial concentration of His tended to be higher for His infusion than for both water and Pro infusions. The AV differences for all EAA were not affected by AA infusion; however, AV differences for Asp, Cys, Glu, and Cit were numerically lowest for Pro infusion, with no changes for other NEAA. Compared to the Control infusion, His infusion decreased extraction efficiency of His by the mammary gland. Although the P treatment did not significantly affect arterial concentration, AV difference, or extraction rate of Pro or Arg when compared to values for the control, it appears that Pro infusion tended to alter extraction efficiency and mammary uptake of Cit and Val. Results of this experiment suggest that His does not limit milk production or milk protein synthesis in high producing lactating dairy cows fed corn silage based rations. Lactation performance and feed efficiency were not improved by abomasal infusion of His and Pro, simultaneously. Unlike results of other studies, increased absorptive supply of both His and Pro did not increase milk protein synthesis in this experiment. Further, abomasal infusion of Pro did not reduce Arg uptake by the mammary gland, which is not consistent with other experiments in which Pro was infused postruminally in lactating cows and goats. However, this work does suggest that postruminal supplementation of Pro might improve feed efficiency and alter milk fat secretion in high producing dairy cows in early lactation.