284 The influence of growth promoting implants at weaning with different supplementations levels on growth performance and ovarian parameters in developing beef heifers

Abstract Administration of a pre-weaning growth promoting implant in beef heifers in Southwestern rangelands can improve growth; however, the effect of administering a second growth promoting implant after weaning on growth and ovarian parameters is unknown. The objective of this study was to determine the effect of supplement level when heifers were administered a second Synovex-C implant at weaning on growth and ovarian parameters. At 2 mo of age heifers (n = 30) were randomly assigned to receive one of three implant treatments: 1) non-implanted (CON), 2) Synovex-C implant at 2 mo of age (BIMP), or 3) Synovex-C implant at 2 and 8 mo of age (WIMP). At 8 mo heifers were randomly assigned to one of two supplement levels (High or Low); thus, creating six treatment groups: High CON (n = 5), Low CON (n = 5), High BIMP (n = 5), Low BIMP (n = 5), High WIMP (n = 5), and Low WIMP (n = 5); assigned in a complete randomized design with a 3 x 2 factorial. Heifers were individually fed supplement three times per week for 25 wk (High 1.26 kg·heifer⁻¹·d⁻¹and Low 0.68 kg·heifer⁻¹·d⁻¹of a 32% CP cube) with refusals weighed back after each feeding. Body weights (BW) were recorded biweekly and grouped in 4 periods (wk 0, 2 to 4, 6 to 14, and 16 to 25). At the end of the supplementation period heifers underwent bilateral ovariectomies. Body weight, height, and length of each ovary was recorded. Surface antral follicles were counted on both ovaries and recorded. Length of the largest follicle was recorded, and follicular fluid (FF) was collected for analysis of estradiol and progesterone concentrations. Ovarian and follicular measurements were analyzed using MIXED procedures in SAS. Average daily gain (ADG) and BW were analyzed as repeated measures using MIXED procedures in SAS. Supplement level × implant interaction tended to influence BW (P = 0.09). Period 4 had increased ADG compared with periods 2 and 3 (P < 0.0001). High heifers had increased ovarian length compared with Low heifers (P = 0.03) and implant tended to increase ovarian length (P = 0.09) compared with CON. Supplement level tended to influence diameter of the largest follicle (P = 0.09). Progesterone FF concentrations tended to be reduced in High heifers compared with Low heifers (P = 0.09). In conclusion, administration of a second Synovex-C implant at weaning did not impact growth performance; however, supplement level tended to hinder follicular parameters.