EVALUATION OF FORAGE SOYBEAN, WITH AND WITHOUT PEARL MILLET, AS AN ALTERNATIVE FORAGE FOR DEVELOPING BEEF REPLACEMENT HEIFERS
Angus-Simmental beef replacement heifers (n=90; BW=366 kg ± 25; BCS=5.53 ± 0.35) were used to evaluate the effects of feeding forage soybean-based silages on heifer BW, BCS, follicular growth and fertility. At 65d prior to timed-artificial insemination (TAI), heifers were allotted by breed, BCS and BW into 3 replications per treatment to receive one of 3 diets; 1) alfalfa haylage (CON), 2) soybean silage (SB) or 3) soybean and pearl millet silage (SBPM). All diets were formulated to meet or exceed nutrient requirements (NRC, 2000) of replacement beef heifers with a targeted gain of 0.79 kg/d. Estrous cyclicity status of heifers was determined by 2 samples of blood taken 10d apart prior to initiation of estrous synchronization and analyzed for circulating progesterone concentrations. Heifers were synchronized for ovulation using a 5-d Co-Synch + CIDR protocol and were observed for estrus on 12h intervals between CIDR removal and TAI. Diameter of the largest antral follicle was determined at time of AI via ultrasonography. Bulls were placed with heifers 10d after TAI for remainder of the breeding season. Pregnancy diagnosis was accomplished via ultrasonography 35 and 66d post-TAI, respectively, for TAI and overall breeding season pregnancy. Data were analyzed with the GLIMMIX and MIXED procedures of SAS for categorical and continuous variables, respectively. Final BW (avg. 414 kg; P ≥ .10) and BCS (avg. 5.28; P ≥ .07) for the heifers were similar among treatments. The proportion of heifers showing estrus prior to TAI (51%) and interval to estrous in those females that exhibited estrus (55h) did not differ among treatments (P ≥ .11). Ovulatory follicle diameter (avg. 11.7mm) was not different (P >.31) among treatments. No differences were noted in pregnancy rate to TAI (avg. = 48%; P > .19) or overall breeding season (avg. = 93%; P > .99) pregnancy rates. In summary, forage soybean-based silages, with and without pearl millet, are an acceptable alternative forage for developing replacement beef heifers.
Keywords: Forage, Beef, Heifer