Akbar Nikkhah - Chief Highly Distinguished Professor, Faculty of Agricultural Sciences, University of Zanjan, Iran

The purpose of this research was to establish prolonged effects of a rumen-protected Met (RPM) product (SmartamineMTM) on reproduction of early-lactation cows underextended high ambient temperatures. A total of 24 Holstein cows including 12 second lactation and 12 higher lactation cows were randomly assigned to either control or RPMsupplementedtotal mixed rations (TMR, 520:480 g/kg forage:concentrate) for 5 months.Cows were offered TMR 3 times daily post-milking plus a top-dress alfalfa hay. The RPMimproved ovary function, estrus expression visibility and body condition score (3 vs. 2.6),while shortening days open (106 vs. 143) and calving interval (387 vs. 421 d). Findings provide evidence for beneficial effects of prolonged RPM provision on reproduction of Holstein cows under concurrent metabolic pressures of early lactation and stressful high ambient temperatures

Dairy cow, Heat stress, Protected methionine, Reproduction