Effects of stage of gestation and feeding regime on intake and apparent total tract digestibility in Holstein × Gyr dairy cows
Two experiments were conducted to determine the effects of stage of gestation (SG) and feeding regime (FR) on DMI and apparent total tract digestibility (ATTD) in Holstein × Gyr dairy cows. Exp. 1: 20 multiparous Holstein × Gyr cows with average initial BW of 495 ± 10.4 kg and age 5 ± 0.3 of yr were used in this experiment. Cows were individually fed a corn silage-concentrate based diet (93% and 7% DMB, respectively). In order to allow cows ad libitum access to feed, feed delivery was adjusted to allow approximately 5% orts daily. Dry matter intake was evaluated at 122, 150, 178, 206, 234 and 262 d of gestation. Overall, DMI decreased (P < 0.05) as days in gestation increased. The decrease in DMI may be associated with reduction in ruminal volume caused by the rapid increase in fetal size during late gestation. Exp. 2: 44 multiparous Holstein × Gyr cows with average initial BW of 480 ± 10.1 kg and age of 5 ± 0.5 of yr were allocated to 1 of 2 FR. Feeding regimes consisted of: 1) ad libitum intake (ADLIB; n=20) and maintenance intake (MAIN; n=24). Maintenance intake was considered as 1.15% of BW. Cows were individually fed a corn silage-concentrate based diet (93% and 7% DMB, respectively) as a total mixed ration, twice a daily. Apparent total tract digestibility was evaluated every 28 d beginning at 122 d of gestation through day 262 by collecting 24 h fecal excretion for the last 5 d of each 28 d period. Within feeding regime, DM digestibility decreased (P < 0.05) as days in gestation increased. An interaction (P < 0.05) existed for DMI and OM apparent digestibility between FR and SG on days 150 and 178 of gestation. Cows fed at MAIN had greater (P < 0.05) DM and OM apparent digestibility than cows fed ADLIB. However, DM and OM apparent digestibility were similar (P > 0.05) for FR at 122, 206, 234 and 262 d of gestation. These data indicate that FR and days in gestation can influence ATTD.
Keywords: dairy cattle, digestibility, pregnancy