PSII-10 The Influence of Synovex-C Growth Implants at Weaning with Different Supplementation Levels on Growth Performance and Antral Follicle Counts in Developing Beef Heifers

Abstract Dormant forage at weaning in Southwestern rangelands may not be nutritionally sufficient to support growth potential of calves administered a growth promoting implant. Therefore, the objective of this study was to investigate the influence of level of supplementation when heifers were administered a Synovex-C implant at weaning on growth and antral follicle counts (AFC). At weaning (8 months old), heifers (n = 17) were stratified by bodyweights (BW) and AFC and assigned to receive one of two levels of supplement (High or Low) and implant (Implant and No Implant; all heifers received a Synovex C implant at 2 months old). Heifers assigned to the Implant group received a second Synovex-C implant at weaning, thus creating four treatment groups: High Implant (n = 4), High No Implant (n = 4), Low Implant (n = 5), and Low No Implant (n = 4). Heifers were utilized in a complete randomized block design with a 2 x 2 factorial. Heifers were individually fed supplement three times a week for 26 weeks with refusals being weighed after each feeding to determine intake. During the receiving phase High and Low heifers were offered 1.94 kg/h/d and 1.17 kg/h/d, respectively, of 20% CP cube for the first 4 weeks of the study. After acclimation High and Low heifers were offered 1.26 kg/h/d and 0.68 kg/h/d, respectively, of 32% CP cube for the remainder of the study. Biweekly BW and monthly body condition scores (BCS) were recorded. Prior to the start of the project and 45 d before the breeding season, AFC were conducted via transrectal ultrasonography. Average daily gain (ADG), BW, and BCS were analyzed as repeated measures in SAS (PROC MIXED). Antral follicle counts were analyzed using MIXED procedures in SAS. Implant, supplement level, implant × supplement level, and implant × supplement level × week did not impact BW or BCS (P ≥ 0.22). Week (P < 0.0001), implant × week (P < 0.0004), and supplement level × week (P < 0.0001) impacted BW. Week (P < 0.0001), implant × week (P = 0.008), and supplement level × week (P = 0.0005) influenced ADG. Implant heifers tended to have increased ADG (P < 0.09) and High Implant heifers tended to have increased ADG compared to the other implant x supplement level treatments (P ≤ 0.09). Body condition score was significantly different across weeks (P < 0.0001). There was no difference between week (P = 0.64) on AFC. Implant (P > 0.22), supplement level (P > 0.43), and implant x supplement level (P > 0.80) did not influence AFC. In conclusion, administration of a second Synovex-C implant at weaning did not impact AFC and feeding implanted heifers at a higher supplementation level tended to improve ADG.