Bioavailability and Effects of Rumen Protected Methionine on Milk Yield and Amino Acid Metabolism in Lactating Crossbred Frisan Cows

Abstract
 
The objective of this study was to evaluate ruminal degradation and productive performance of lactating cows fed rations supplemented with one of two different sources of methionine products [methionine hydroxy analogue (HMB) or DL-methionine (DL-Met)]. The effect of the two sources of methionine on ruminal degradations, milk yield and plasma essential amino acids concentrations were measured in two experiments. In experiment 1, the ruminal degradation of methionine was assessed using in situ bag techniques with three Barki female sheep (with an average of 44kg) fitted with permanent ruminal fistula. In the second experiment nine lactating Crossbred Friesian multiparous cows in similar condition were randomly assigned to three experimental treatments to determine milk yield and milk composition. Methionine concentration was assayed in blood plasma. The obtained results indicated that the rate of disappearance of HMB was significantly (P>0.05) lower than DL-Met. (52.12. vs. 86.73). While the highest (P>0.05) rumen escapes were recorded for HMB. Methionine hydroxy analogue had more resistance to ruminal degradation than DL-Met. The results also revealed that daily milk production and FCM of cows fed 25g day HMB was significantly (P>0.05) higher than those fed the control or ration supplemented  with DL-Met. Treatment had no effect on percentage of lactose. However, total solids, fat and milk protein significantly (P>0.05) increased with 25g day HMB supplementation. The results also showed that methionine concentration in blood plasma increased significantly (P>0.05) with cows fed ration supplemented with HMB compared with those fed control ration or those fed ration supplemented with DL-Met. Results of the present study also showed that supplementation of 25g day HMB improved, bioavailability of methionine and promoted amino acid utilization in lactating cows which increase milk yield