Influence of late gestation drylot rations differing in protein degradability and fat content on beef cow and subsequent calf performance

Spring-calving, mature cows (n = 191 total) and their progeny were used to evaluate the effects of late gestation drylot rations differing in RUP and fat content on cow performance as well as performance and carcass characteristics of subsequent progeny. Cows were blocked by BW and anticipated calving date and assigned to 16 pens. Pens were randomly allotted to 1 of 2 treatments: limit-fed corn coproducts and ground cornstalks (COP; TDN = 64.4%, CP = 11.1%, RDP = 60.2% of CP, and fat = 5.1%) or limit-fed ground mixed, cool-season grass hay (HY; TDN = 55.7%, CP = 9.5%, RDP = 86.0% of CP, and fat = 2.3%). Treatments were limit fed as isocaloric, isonitrogenous rations from 88 ± 11 d pre-partum to calving. All cows were fed a common diet postpartum. Cow BW and BCS were collected at the beginning of the feeding period, within 48 h after calving, and at breeding. Calf BW was collected at birth and at 64 ± 11 and 124 ± 11 d of age. Milk production was determined using the weigh–suckle–weigh technique at 64 ± 11 and 124 ± 11 d postpartum. At 124 ± 11 d of age, steers (n = 68) and nonreplacement heifer calves (n = 25) were weaned and placed on a common feedlot diet with individual feed intake monitored using GrowSafe. Feedlot calves were slaughtered at a commercial facility 35 ± 10 d after a minimum ultrasound 12^th-rib fat thickness estimation of 0.9 cm. After calving, cow BW was greater (P < 0.01) and BCS was greater (P < 0.01) for cows fed COP than for cows fed HY. Calf birth BW was greater (P = 0.04) for those born to cows fed COP with no difference (P = 0.43) in percentage of unassisted births across treatment. Cows fed HY were lighter (P < 0.01) at breeding with lower BCS (P = 0.03); nevertheless, overall pregnancy rate was not different (P = 0.80). No differences (P ≥ 0.22) in milk production were detected. For feedlot progeny, initial feedlot BW, final BW, and days on feed were not different (P ≥ 0.23), and as a result, no difference (P = 0.21) in feedlot ADG was detected. Feedlot DMI and G:F were not different (P ≥ 0.19) across treatments. Feedlot calf health was monitored with no differences (P ≥ 0.68) in morbidity and mortality observed. No differences (P ≥ 0.27) were detected for HCW, LM area, backfat, marbling score, yield grade, or KPH. Increased dietary RUP and fat content during late gestation increased cow BW and BCS but did not alter milk production, subsequent reproduction, or subsequent calf performance or carcass characteristics.