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Title: Failure of differences in prepubertal dietary intake to affect ovarian development in pubertal beef heifers

item Echternkamp, Sherrill
item Eborn, Douglas
item Cushman, Robert - Bob

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 2/25/2011
Publication Date: 7/1/2011
Citation: Echternkamp, S.E., Eborn, D.R., Cushman, R.A. 2011. Failure of differences in prepubertal dietary intake to affect ovarian development in pubertal beef heifers [abstract]. Journal of Animal Science. 89 (E-Supplement 1):93 (Abstract #M246).

Interpretive Summary:

Technical Abstract: Developing replacement heifers on lower energy diets to a lighter body weight at first breeding can reduce input costs but may impede follicular development and onset of puberty. The objective was to determine whether lower dietary intake prepubertally impedes ovarian development in purebred or crossbred heifers. In 2009 and 2010, 8-mo-old Angus and composite MARC II heifers were assigned equally by body weight and genetic line (n = 120 / line) to receive either a low- (LE) or high- (HE) energy diet to achieve an ADG of 0.45 or 0.9 kg/d for 180 d or 55 vs. 65% of mature BW at 14 mo of age. At 14 mo, heifers were monitored twice daily for estrus behavior for 21 d. Total number of antral follicles (AFC), ovarian length and height, and preovulatory follicle diam. were measured by transrectal ultrasonography at about 12 h after estrus; corpus luteum (CL) diam. was measured 7 to 14 d later. Uterine horn diam. was only measured in 2010. Data were analyzed by ANOVA with diet, line, and year as independent variables and their 2-way interactions. At 14 mo, HE heifers were heavier (419.4 vs. 364.9 ± 7.1 kg) and fatter (6.8 vs. 5.5 ± 0.1 BCS) than LE heifers (P < 0.01); LE heifers were 11% heavier in 2010 than 2009 (diet x year; P < 0.01). Puberty occurred in 94.6% of heifers by 14 mo of age. Size of preovulatory follicle (13.8 ± 0.2 mm), AFC (22.2 ± 0.6), ovary (length = 26.5 ± 0.3 mm; height = 15.1 ± 0.2 mm), CL (19.3 ± 0. 3 mm), and uterine horn diam. (11.6 ± 0.2 mm) did not differ between HE and LE, but follicle diam. (14.3 vs. 13.2 ± 0. 2 mm; P < 0.01) and ovarian length (26.4 vs. 25.3 ± 0.4 mm; P = 0.07) were greater for MARC II vs. Angus heifers. AFC was correlated with ovarian length (r = 0.56; P < 0.01), and CL diam. was correlated with preovulatory follicle diam. (r = 0.34; P < 0.01). Results indicate that AFC and ovarian size in pubertal heifers are not influenced by differences in prepubertal growth and body condition associated with diet. USDA is an equal opportunity provider and employer.