Use of mixed rations with different access time to pastureland on productive responses of early lactation Holstein cows

The intensification of milk production has required the development of new feeding strategies such as the use of mixed rations either with or without access to grazing. The aim of this study was, to determine milk production and composition, body condition score (BCS), live weight (LW) and grazing behaviour of Holstein dairy cows subject to diets combining mixed rations and herbage during their first 10-wk of lactation (period 1). In addition, both the behavioural adaptation and productive response of cows fed 100% mixed ration when returning to grazing for a 20 days period were examined (period 2). An incomplete randomized block design was used, with 41 early lactation multiparous cows, assigned to treatments: G0 (confined cows fed 100% mixed ration), G1 (6 h access to paddocks+50% mixed ration) and G2 (9 h access to paddock+50% mixed ration). In a second period (11 to 13- wk of lactation), G0 (Post-TMR) cows were managed as G1, with G1 as the control treatment. During the first period, G0 cows produced more milk (37.2 vs 33.7 and 33.9±0.92 L/d; P<0.0001) and more protein (1.25 vs 1.12 and 1.13±0.038 kg/d; P=0.006) than G1 and G2. Nevertheless, no significant differences in fat and lactose production, and output of milk energy were found between G0 and G2 cows. With more access time to the paddock G2 cows could express a higher herbage dry matter intake (DMI) than G1 cows through a higher total grazing time. However, no differences were found on milk production and composition between G1 and G2 cows, probably due to a higher maintenance energy requirement for G2 cows. In period 2 no significant differences were detected in milk production, milk fat and protein production, BCS or LW between Post-TMR and G1 cows. Also, grazing behaviour was not different between G1 and Post-TMR cows, suggesting a prompt adaptation of G0 cows to grazing. It can be concluded that 100% mixed ration systems had higher milk production than grazing plus TMR systems in early lactation. An increase in access time to pastureland allowed higher herbage intake, although with no significant differences in milk energy output. The use of fresh pasture to replace mixed rations after the first 65 DIM allowed maintaining high milk and solids production.