|Cushman, Robert - Bob|
|FERRELL, CALVIN - Retired ARS Employee|
Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 3/7/2010
Publication Date: 7/1/2010
Citation: Echternkamp, S.E., Cushman, R.A., Ferrell, C.L. 2010. Effect of Dietary Energy on Ovarian Development and Fertility in Postpuberal Beef Heifers [abstract]. Journal of Animal Science. 88 (E-Supplement 2):115. (Abstract #M300).
Technical Abstract: Beef producers are advised to develop replacement heifers to 65% of mature BW, but reports indicate this BW could be reduced to lower input costs. To determine whether lower dietary intake impedes ovarian development and fertility in purebred or crossbred heifers, Angus (n = 60) and MARC II (¼ Angus, ¼ Hereford, ¼ Gelbvieh, and ¼ Simmental; n = 60) heifers were fed either a high (HE) or low (LE) energy diet for 180 d postweaning to achieve 65 vs. 53% of mature BW at first breeding. At 14 mo of age, heifers were housed with fertile bulls for 47 d. Estrus was monitored for 21 d, and 12 h after estrus, ovaries were ultrasounded in one-half of the heifers to measure ovarian length and height, preovulatory follicle diam., and total number of antral follicles (AFC); corpus luteum (CL) diam. and blood progesterone were measured 7 to 14 d after estrus. Data were analyzed by SAS PROC GLM or GLIMMIX with diet and genetic line as independent variables; 2-way interactions were not significant. Initial BW (282.8 kg) did not differ but, at breeding, HE heifers were heavier (429.4 vs. 344.8 ± 7.1 kg) and fatter (6.9 vs. 5.0 ± 0.1 BCS) than LE heifers (P < 0.01); experimental ADG was 0.81 vs. 0.35 ± 0.02 kg/d (P < 0.01). Puberty occurred in 93.3% of heifers prebreeding. Size of preovulatory follicle (13.7 ± 0.2 mm), ovary (length = 24.2 ± 0.3 mm; height = 13.3 ± 0.2 mm), CL (19.4 ± 0.5 mm), and AFC (23.4 ± 1.3) did not differ between HE and LE, but follicle diam. (14.3 vs. 13.1 ± 0.3 mm; P < 0.01) and ovarian length (25.1 vs. 23.1 ± 0.7 mm; P = 0.05) were greater for MARC II vs. Angus heifers. Ovarian size was correlated with AFC (r = 0.64; P < 0.01). Plasma progesterone was greater for HE vs. LE heifers (5.3 vs. 4.3 ± 0.3 ng/mL; P < 0.05), but CL diam. (19.4 ± 0.5 mm) was not affected by diet or line. Pregnancy rate did not differ between diets but tended (P = 0.07) to be greater for MARC II vs. Angus (80 vs. 65%). Developing yearling beef heifers to 53% of mature BW did not impede ovarian development or heifer pregnancy rate.