Effect of rumen undegradable fat at two levels of undegradable intake protein in early lactation through mid-lactation of dairy cows

Sixty multiparous Holstein cows were fed four concentrates formulated to contain 0 or .45 kg supplemental fat (SF) and 16% CP of which 36 or 42% was undegradable intake protein (UIP). A commercial blend of hydrolyzed feather meal and conventional cooker-dried blood meal along with dried distillers grain were used to increase the UIP percentage. Prilled, partially saturated beef tallow was the supplemental fat source. The control diet (36% UIP and 0 SF) was fed during the covariate period from calving through wk 4. At wk 5 postpartum, cows were switched to one of four experimental concentrates which they received for the following 17 wk: control. Fat (36% UIP and .45 kg SF), UP (42% UIP and 0 SF), and Fat + UP (42% UIP and .45 kg SF). The main effects were increased UIP and SF.

Milk yield, concentrate intake, body weight and body condition score were not different due to treatment. Fat treatment tended to increase yield of four percent FCM (42.9 vs 40.8 kg/d) and milk protein (1.32 vs 1.23 kg/d). UP treatment had no significant effects. The interaction of Fat + UP decreased milk fat percent (2.79 vs 3.10%) and increased milk protein percent (3.12 vs 3.02%), which supports increased UIP content in the diet when SF is fed.

Ultrasound measurements taken at the withers, between the twelfth and thirteen rib, and midpoint of the hooks and pins were compared with body condition scores (scale 1 = thin, 5 = fat). A low correlation between ultrasound measurements and body condition score indicates that body condition in dairy cattle should not be predicted by ultrasound measurements.