Effect of restricting time at pasture and concentrate supplementation on herbage intake, grazing behaviour and performance of lactating dairy cows

• Restricting time at pasture increased grazing time and initial grazing bout of milk cows.
• Restricting time at pasture reduced rumination and idling times of milk cows.
• Restricting time at pasture did not affect herbage intake.
• Restricting time at pasture and supplement level affected grazing behaviour and digestion.
• Behaviour changes showed milk cow plasticity to solved forage restriction.

Restricting time for grazing and concentrate supplementation affects feeding motivation, altering grazing behaviour, and performance of grazing ruminants. This study evaluated the combination of three lengths of restricting time at pasture and two levels of concentrate supplementation on behaviour, intake, and productive performance of dairy cows. Times out of pasture were 0, 4 (0800–1200 h) and 8.5 (0800–1630 h) hours. Levels of concentrate supplementation were 3 and 6 kg DM/cow/day. Measurements were: herbage dry matter intake and digestibility, grazing, ruminating and idling time, bite rate, milk yield and composition, as well as changes in live weight and body condition score. Restricting time at pasture increased (P<0.01) grazing time and length of the initial grazing bout (P<0.01) and reduced (P<0.01) rumination and idling times. Restricting time at pasture did not affect herbage intake or milk yield; however, it reduced milk fat concentration (P<0.01). Supplementation level reduced (P<0.05) grazing time, but did not affect rumination and idling times. Bite rate was the greatest in cows that were not restricted and had the lowest level in R8,5S6 groups (P<0.01). Supplementation reduced herbage dry matter intake, and herbage and total organic matter digestibility (P<0.01). Supplementation increased milk yield (P<0.05) without effects on milk composition. Modulation of grazing behaviour in response to restricting time at pasture maintained herbage dry matter intake. Changes in grazing behaviour in response to restricting time at pasture plus concentrate supplementation counteract restrictions of restricted time at pasture and thereby help to maintain herbage and energy intake without negative effects on milk production.