0619 Grazing management: milk production and composition of dairy cows grazing elephant grass

The objective of this experiment was to evaluate the effects of strategies of rotational grazing management on milk yield and composition of dairy cows grazing elephant grass (Pennisetum purpureum Schum. cv. Cameroon) from December 2015 to February 2016. Treatments corresponded to management strategies characterized by the pregrazing targets of 95% and maximum canopy light interception during regrowth (equivalent to 100 and 135 cm; LI95% and LIMax, respectively). The postgrazing target was the same and corresponded to 50% of the pregrazing height. Midlactation Holstein × Jersey cows were separated into two groups according to BW, days in milk, age, lactation number, and daily milk yield. The 2.5-ha experimental area was divided up into two sets of 18 paddocks (700 m2). Twenty-two cows (487.5 ± 13.1 kg) were used as testers and a variable number was used to adjust stocking rate. Milking was performed twice a day at 0500 and 1530 h, milk yield was measured in a daily basis, and milk composition was measured at 10-d intervals. The amount of concentrate mix fed to cows was based on the average milk production for the groups (1 kg of concentrate:3 kg of milk) and offered in two daily individual meals just before milking. The effective values of pre- and postgrazing heights were 100.8/50.5 and 135.6/68.6 cm with average stocking rates of 9.2 and 6.0 cows/ha for LI95% and LIMax, respectively. The results were analyzed using the PROC MIXED of SAS (α = 0.05). Management based on the LI95% target resulted in an 18.5% increase in milk production (19.2 vs. 16.2 kg of 3.5% fat corrected milk cow−1 d−1), lactose (854 vs. 710 g d−1), protein (578 vs. 519 g d−1) and fat yield (677 vs. 569 g d−1), despite no difference in fat content. Protein content was higher for LIMax (3.28 vs. 3.07%) and urea N was higher for LI95% (13.17 and 11.83 mg dL−1). The results suggest that the LI95% pregrazing target correspond to a better management strategy because it resulted in increased milk and milk solids production per cow and stocking rate, resulting in increased productivity.