The effect of a zero-grazed perennial ryegrass, perennial ryegrass and white clover, or multispecies forage on the dry matter intake, milk production and nitrogen utilization of dairy cows in mid-late lactation

Abstract

The objective of this experiment was to assess the impact of forage type on the DMI and milk production of mid-late lactation dairy cows. Perennial ryegrass (Lolium perenne) (PRG), PRG and white clover (Trilfolium repens) (PRGWC) and multispecies forage containing PRG, timothy (Phleum pratense), WC, red clover (Trifolium pratense), chicory (Cichorium intybus), and plantain (Plantago lanceolata) (MULTI), were compared using 24 cows in a three-period Latin square changeover design experiment. Cows were acclimatized to dietary treatments for 14 days, before entering a 21-day sampling period. Animals were housed indoors throughout the experiment, with access to forage treatments via computerized feeding boxes that recorded daily forage fresh weight intake and feeding behavior. Forage was harvested using a zero-grazer and feed boxes filled throughout the day. Forage dry matter was determined daily and forage DMI subsequently calculated. Milk yield (MY) was recorded daily, with milk composition (fat, protein, lactose) measured weekly. Once per sampling period, blood and rumen samples were collected. The partitioning of dietary nitrogen into milk, feces and urine was assessed for 6-days in each sampling period. Data was analyzed in SAS using PROC MIXED and checked for normality using UNIVARIATE. Forage botanical composition changed from period 1 to period 2 and 3, leading to significant differences in chemical composition between periods. Despite this, dry matter intake was consistently higher (P <0.05) for MULTI (20.14 kg DM) and PRGWC (18.30 kg DM) compared to PRG (17.06 kg DM). Offering cows MULTI increased daily MY (21.20 kg/d; P <0.001) compared to PRG (20.28 kg/d) and PRGWC (20.19 kg/d). Cows offered PRG made fewer visits to the feed box (P <0.001) and had a reduced meal size (kg/visit) (P <0.001) compared to PRGWC and MULTI. Offering cows MULTI reduced UN concentration (%) by 20% compared to either PRG or PRGWC. Perennial ryegrass resulted in higher dietary nitrogen use efficiency (NUE) compared to PRGWC or MULTI, though this effect was not consistent between periods. These results show that multispecies forages can increase milk production when offered to cows housed indoors. However, despite MULTI resulting in a lower UN concentration, cows offered PRG had a higher dietary NUE, likely due to a lower N intake.