Reproductive performance of Nellore heifers raised in extensive system undergoing different vaccination protocols in fixed-time artificial insemination (FTAI)

ABSTRACT: This study evaluated the reproductive performance of Nellore heifers without previous vaccination undergoing fixed-time artificial insemination (FTAI) and subsequent natural breeding under different vaccination protocols against infectious bovine herpesvirus 1 (BHV-1), bovine viral diarrhea virus (BVDV), and bovine leptospirosis (BL). A total of 763 animals were included; the group assignment was as follows: T1, control without vaccination; T2, vaccination against BL; T3, vaccination against BHV-1and BVDV; T4,vaccination against combination of BL + BHV-1and BVDV. Vaccination was started 30 days before FTAI (D-40), and a booster dose was administered at D-10. Serological tests were used to verify the occurrence rate of natural infection by BL, BHV-1, and BVDV. Initial pregnancy was diagnosed at D30, D60, and D120 after FTAI. Final pregnancy rates were evaluated by group, weight, body-condition score, occurrence of estrus, inseminator, bull, and occurrence of abortions or embryonic death. In all groups, results indicated seropositivity of 100% for leptospirosis, 77.0-94.0% for BHV-1, and 64.0-87.0% for BVDV. The vaccination protocol was not a significant influencing factor of pregnancy rate and embryonic or fetal mortality; whereas, animal weight at the beginning of the breeding season and presence of estrus at FTAI were significant influencing factors of pregnancy rate. The vaccination protocol had no interference with the reproductive performance of the experimental groups.摘要：本研究评估了未预先接种疫苗的内洛尔青年母牛（Nellore heifers）在定时人工授精（fixed-time artificial insemination, FTAI）及后续自然配种模式下，针对牛传染性疱疹病毒1型（infectious bovine herpesvirus 1, BHV-1）、牛病毒性腹泻病毒（bovine viral diarrhea virus, BVDV）及牛钩端螺旋体病（bovine leptospirosis, BL）的不同疫苗接种方案对其繁殖性能的影响。本研究共纳入763头试验牛只，试验分组如下：T1为未接种疫苗的对照组；T2为仅接种BL疫苗的组；T3为仅接种BHV-1与BVDV疫苗的组；T4为联合接种BL、BHV-1及BVDV疫苗的组。疫苗接种于FTAI前30天启动（记为D-40），并于D-10追加一剂加强针。通过血清学检测统计BL、BHV-1及BVDV的自然感染发生率。分别于FTAI后第30天、第60天及第120天确诊初始妊娠状态。最终妊娠率按试验组、初始体重、体况评分、发情情况、人工授精操作人员、种公牛以及流产或胚胎死亡发生情况进行分组评估。所有试验组的血清学检测结果显示：BL血清阳性率为100%，BHV-1为77.0%~94.0%，BVDV为64.0%~87.0%。疫苗接种方案对妊娠率及胚胎/胎儿死亡率无显著影响；而配种季初始体重与FTAI时的发情状态是妊娠率的显著影响因素。疫苗接种方案对试验组的繁殖性能无干扰作用。