Abstract

The objective of this experiment was to investigate the relationship between residual feed intake (RFI) and parameters associated with reproductive efficiency in growing beef heifers. One hundred and seventy-nine replacement beef heifers (Bos taurus and Bos indicus-influenced) were enrolled in a retrospective cohort design. Heifers were assigned to a 70-d feed efficiency test, and results were utilized to retrospectively classify heifers into low (n = 51), medium (n = 66), or high (n = 62) RFI groups based on their individual RFI values. Blood samples were collected weekly throughout the feed efficiency test and breeding season, which were analyzed for plasma concentration of progesterone to determine age at puberty (PUB). By design, residual feed intake differed among RFI groups where high (1.21 ± 0.08 kg/d) had greater (P < 0.01) RFI than medium (0.00 ± 0.08 kg/d) and low RFI groups (–1.49 ± 0.09 kg/d), and medium had greater (P < 0.01) RFI than low RFI heifers. Yet, no differences were observed between breed types for RFI (P = 0.53). Average daily gain (ADG) differed between breed types where Bos taurus heifers had greater ADG (P = 0.02) than B. indicus-influenced heifers. Furthermore, ADG tended (P = 0.08) to differ among RFI groups, where medium RFI heifers tended to have reduced ADG compared with low and high RFI heifers. No differences were determined between breed types for gain-to-feed ratio (G:F; P = 0.20; however, G:F differed among RFI groups and was greater (P < 0.01) in low vs. high, and low vs. medium RFI heifers. The percentage of cycling heifers by the start of the breeding season differed (P = 0.03) by RFI group, where a greater percentage of low RFI heifers were cycling compared with high RFI heifers. A difference was determined on PUB between breed types (P = 0.03), where Bos taurus (393.40 ± 4.64 d) heifers had a reduced PUB compared with B. indicus-influenced (406.90 ± 5.07 d) heifers. In addition, PUB differed by RFI group where low (385.96 ± 6.20 d; P < 0.01) and medium (398.47 ± 5.47 d; P = 0.02) RFI heifers had a reduced PUB compared with High RFI heifers (416.03 ± 5.58 d). In conclusion, more feed efficient heifers attained PUB earlier than less feed efficient heifers. Therefore, selection of heifers for feed efficiency may positively impact reproductive performance of replacement beef heifers.

中文翻译：

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Bos taurus 和 Bos indicus 影响的替代牛肉小母牛饲料效率与青春期的关系

摘要

本实验的目的是研究剩余饲料摄入量 (RFI) 与生长小母牛繁殖效率相关参数之间的关系。179 头替代小母牛（受Bos taurus和Bos indicus影响）被纳入回顾性队列设计。小母牛被分配到一个 70 天的饲料效率测试，结果被用来回顾性地将小母牛分为低 ( n = 51)、中 ( n = 66) 或高 ( n= 62) 基于 RFI 值的 RFI 组。在整个饲料效率测试和繁殖季节每周收集血样，分析血浆孕酮浓度以确定青春期年龄 (PUB)。根据设计，RFI 组的剩余采食量不同，其中高 (1.21 ± 0.08 kg/d ) 的 RFI大于 ( P < 0.01) 中 (0.00 ± 0.08 kg/d) 和低 RFI 组 (–1.49 ± 0.09 kg/d) )，并且中等RFI 比低 RFI 小母牛更大 ( P < 0.01)。然而，在 RFI 的品种类型之间没有观察到差异（P = 0.53）。品种类型之间的平均日增重 (ADG) 不同，其中Bos taurus小母牛的 ADG ( P = 0.02) 高于B. indicus- 影响的小母牛。此外，ADG 倾向于（P = 0.08）在 RFI 组之间有所不同，其中与低和高 RFI 小母牛相比，中等 RFI 小母牛的 ADG 往往降低。不同品种之间的增重饲料比没有差异（G:F；P = 0.20；然而，RFI 组之间的 G:F 不同，低与高、低与高、低与高的G：F 更大（P < 0.01）。中等 RFI 小母牛。到繁殖季节开始时循环小母牛的百分比因 RFI 组而不同（P = 0.03），其中低 RFI 小母牛的循环百分比高于高 RFI 小母牛。差异是在品种之间的 PUB 上确定的类型 ( P = 0.03)，其中Bos taurus与受B. indicus影响的 (406.90 ± 5.07 天) 小母牛相比，(393.40 ± 4.64 天) 小母牛的 PUB 减少。此外，PUB 因 RFI 组而异，其中低 (385.96 ± 6.20 d; P < 0.01) 和中 (398.47 ± 5.47 d; P = 0.02) RFI 小母牛与高 RFI 小母牛 (416.03 ± 5.58 d) 相比 PUB 降低。总之，饲料效率高的小母牛比饲料效率低的小母牛更早达到 PUB。因此，选择小母牛以提高饲料效率可能会对替代肉牛的繁殖性能产生积极影响。