Grazing behaviour and nutrient intake of dairy cows is affected by milking order and daily time at pasture

Context The average herd size on Australian dairy farms has increased in recent decades, with herds of over 500 cows producing one-third of the nation’s annual milk. Aims This 16-day experiment aimed to simulate a large herd of cows progressively returning to the paddock after milking, to understand how grazing behaviour, nutrient intake and farm profit are affected when cows consistently spend prolonged periods of time away from pasture. Methods Forty spring-calving, Holstein-Friesian cows returned to the paddock in five groups at 45-min intervals after each milking. Cows grazed perennial ryegrass pasture offered at an allowance of 25 kg of dry matter (DM)/cow per day (to ground level), and were fed 6.0 kg of DM/cow per day of a concentrate mix in the dairy during milking. During the 5-day measurement period, grazing behaviour was measured using noseband sensors and pedometers; the n-alkane technique was employed to determine individual cow pasture dry matter intake; and the depletion of pasture mass and nutritive characteristics over a grazing session was measured. Key results There was no difference in daily total eating time, but cows that arrived at the paddock 135 min after the first cows had longer initial grazing bouts in the a.m. grazing session. Milk yield declined linearly as cows spent more time away from pasture, with a 6 kg/cow per day difference between the first and last cows. Higher metabolizable energy and crude protein intakes were observed in cows that had higher pasture intakes. Immediate profit was lowest for the last cows to return to the paddock by AU$2.48/cow per day. Conclusions Total daily eating time is not affected by milking order, but no change in grazing time would be able to counteract the effect of reduced pasture quantity and quality for the later-milked cows to enable them to increase their nutrient intake. The influence of milking order on milk production also leads to lower profit for cows that return to the paddock later. Implications Understanding how time away from pasture affects grazing behaviour and nutrient intake will allow the development of mitigation strategies to be investigated.