259 Effect of stair-step nutritional programming on ovarian development in replacement beef heifers

Abstract

Abstract Based on recent research, it may be possible to influence the number of primordial follicles in the ovaries during the first year of life. Spring-born Angus crossbred heifers (n = 40) were utilized to determine the effect of a stair-step development system on growth and reproduction. Heifers (11 mo) were assigned to 1 of 4 treatments: 1) constant gain drylot (CG-d), 2) stair-step drylot (SS-d), 3) constant gain native range (CG-r), and 4) stair-step native range (SS-r). Heifers were fed individually with a constant gain target of 0.5 kg/d, while stair-step heifers were targeted to gain 0.25 kg/d the first 45 d (period 1) and 0.75 kg/d over the last 45 d (period 2). All heifers were ovariectomized on d 90. Heifer BW was similar on d 0 and d 45; however, native range heifers had an increased BW at d 90 (P < 0.01) compared to drylot heifers. Period 1 and overall ADG was greater in native range heifers (P < 0.01) compared to drylot heifers. During period 2 CG-r and SS-r heifers had an increased ADG compared to CG-d and SS-d heifers, with SS-d having an increased ADG (P = 0.03) compared to CG-d heifers. Reproductive tract score was similar (P = 0.19) between treatments. Ovarian weight and preovulatory follicle diameter were decreased (P < 0.02) in drylot compared to native range heifers. Primary follicles/section was increased (P = 0.05) in stair-s (P = 0.04) in SS-r and SS-d heifers compared to CG-d heifers, with CG-r similar to all other treatments. Differences in diets between drylot and native range positively influences mechanisms controlling primordial follicle activation. Developing heifers on a stair-step nutritional program resulted in a larger ovarian reserve, potentially resulting in an increase in reproductive longevity.