I.M. Abd El-Razek

Animal Production Department, Faculty of Agriculture, KafrElsheikh University, Egypt.

Abstract :

A total of 30 Friesian dairy cows aged 31-59 months with an average live body weight 502.6 kg were divided into three similar groups based upon age, live body weight and milk yield to evaluate the effect of oral L-tyrosine administration on milk yield and reproductive performance of Friesian dairy cows at day 121 or 140 post calving (during mid-lactation). Cows in the first group (G1) were fed concentrate feed mixture (CFM) and considered as a control group. While, those in the 2^nd (G2) and 3^rd (G3) groups were received an oral dose of 50 g/cow L-tyrosine at day 121 and 140 of postpartum, respectively. Results revealed that L-tyrosine treatment significantly (P<0.05) increased the average daily milk production during the 2^nd four months of lactation in term of actual milk yield (AMY), 4% fat corrected milk yield (FCMY), milk composition, and decreased the number somatic cell count (SCC) in milk compared to the that of the control one. L-tyrosine treatment was also improved reproductive performance and overcomes reproductive problems associated with ovarian activity such as incidence of estrus, interval from calving to the first estrus, postpartum first service, days open, number o.

f services per conception and finally improved conception rate. In conclusion: based upon the results obtained in this study,L-tyrosine could be used for treating cows during postpartum periods to improve cow’s reproductive performance by overcoming their reproductive problems and enhancing milk production and its composition.

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