Protected methionine prolonged provision improves summer production and reproduction of lactating dairy cows

The objective was to establish prolonged effects of a rumen-protected Met (RPM) product (SmartamineM) on milk production and reproduction of high-producing early-lactation cows under extended very high ambient temperatures. Twenty four fresh Holstein cows (27 +/- 9 days in milk, 617 kg b.wt., 2.8 body condition score) including 12 second lactation and 12 higher lactation cows were randomly assigned to either control or RPM-supplemented total mixed rations (TMR, 520:480 g kg(-1) forage:concentrate), and were fed continuously for 5 months. Cows were offered TMR 3 times daily post-milking plus a top-dress alfalfa hay. The study was conducted from May through November of 2009 in central Iranian province of Isfahan. The RPM group had consistently greater 5-month-long average DM intake (21.9 vs. 19.1 kg day(-1)), milk yield (42.4 vs. 37.4 kg day(-1)), milk fat content (33 vs. 27.5 g kg(-1)), fat yield (1.40 vs. 1.04 kg day(-1)), milk protein content (29.6 vs. 27.5 g kg(-1)) and protein yield (1.25 vs. 1.02 kg day(-1)). Mature cows tended to produce more milk (42.2 vs. 37.6 kg day(-1)) and milk fat (1.30 vs. 1.13 kg day(-1)) than second lactation cows. The RPM significantly improved 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 compelling evidence for beneficial effects of prolonged RPM provision on feed intake, milk production, and reproduction of Holstein cows under concurrent metabolic pressures of early lactation and stressful high ambient temperatures.