Production parameters of autumn-calving cows offered either a total mixed ration or grazed grass plus concentrate during early lactation

Abstract

The objective of this experiment was to measure the milk yield and composition from cows offered a total mixed ration (TMR) compared with those grazing grass and offered different quantities of concentrates during the first 6wk of lactation when the experimental diets were offered, and for the remainder of lactation when all animals were offered a similar diet. Forty-eight (18 primiparous and 30multiparous) Holstein-Friesian dairy cows (mean calving date, September 12±15d) were randomly assigned to a 4-treatment (n=12) randomized block design experiment. The 4 treatments were (1) housed indoors and offered ad libitum TMR (ITMR; control); (2) grazed grass and 1kg (dry matter; DM) of concentrate/cow per day (G1); (3) grazed grass and 4kg (DM) of concentrate/cow per day (G4); (4) grazed grass and 8kg (DM) concentrate/cow per day (G8). Experimental treatments were imposed starting on September 29, 2008, and lasted for 6wk. Following the 6-wk experimental period, all cows were managed similarly. They were offered a TMR until turnout to pasture the following spring (February 10, 2009) and grazed grass from then until drying off. The deferred effect of the 6-wk experimental period on production parameters was monitored during a 13-wk period, and total lactation production was also investigated. During the 6-wk experimental period, total dry matter intake (DMI) was greater for ITMR and G8 cows compared with G4 and G1 cows. Differences in total DMI, measured during the 6-wk period when treatments were imposed, were reflected in milk yield. During the 6-wk period, ITMR cows had the greatest milk yield (27.3kg/cow per day) and G1 cows had the lowest (21.1kg/cow per day). Milk yields of the G4 and G8 cows were similar (24.8kg/cow per day). We detected no effect of treatment on milk fat (3.77%) or milk protein (3.25%) concentration. Treatment did affect milk solids yield (MSY): ITMR cows yielded 1.90kg/cow per day, which did not differ from that of the G8 cows (1.75kg/cow per day), G1 cows had the lowest MSY (1.53kg/cow per day) and that of G4 (1.69kg/cow per day) cows was lower than ITMR but not different from G8. At the end of the 6-wk experimental period, the ITMR and G8 cows had greater body weight (525kg/cow) than the G4 and G1 cows (502kg/cow). Treatment had no effect on milk yield or composition during the remainder of the lactation and no effect on cumulative lactation milk yield or composition. The data from this experiment indicate that herbage can be incorporated into the diet of early-lactation, autumn-calving dairy cows without any negative consequences on total lactation milk yield or composition.