School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland D04 N2E5.
Laboratory of Animal Reproduction, Department of Biological Sciences, Biomaterials Research Cluster, Bernal Institute, Faculty of Science and Engineering, University of Limerick, Limerick, Ireland V94 PT85.
J Dairy Sci. 2021 Jun;104(6):7262-7271. doi: 10.3168/jds.2020-19900. Epub 2021 Mar 11.
Despite passing routine laboratory tests of semen quality, bulls used in artificial insemination (AI) exhibit a significant range in field fertility. The objective of this study was to determine whether subfertility in AI bulls is due to issues of sperm transport to the site of fertilization, fertilization failure, or failure of early embryo or conceptus development. In experiment 1, Holstein-Friesian bulls (3 high fertility, HF, and 3 low fertility, LF) were selected from the national population of AI bulls based on adjusted fertility scores from a minimum of 500 inseminations (HF: +4.37% and LF: -12.7%; mean = 0%). Superovulated beef heifers were blocked based on estimated number of follicles at the time of AI and inseminated with semen from HF or LF bulls (n = 3-4 heifers per bull; total 19 heifers). Following slaughter 7 d later, the number of corpora lutea was counted and the uteri were flushed. Recovered structures (oocytes/embryos) were classified according to developmental stage and stained with 4',6-diamidino-2-phenylindole to assess number of cells and accessory sperm. Overall recovery rate (total structures recovered/total corpora lutea) was 52.6% and was not different between groups. Mean (± standard error of the mean) number of embryos recovered per recipient was 8.7 ± 5.2 and 9.4 ± 5.5 for HF and LF, respectively. Overall fertilization rate of recovered structures was not different between groups. However, more embryos were at advanced stages of development (all blastocyst stages combined), reflected in a greater mean embryo cell number on d 7 for HF versus LF bulls. Number of accessory sperm was greater for embryos derived from HF than for LF bulls. The aim of experiment 2 was to evaluate the effect of sire fertility on survival of bovine embryos to d 15. Day 7 blastocysts were produced in vitro using semen from the same HF (n = 3) and LF (n = 3) bulls and transferred in groups of 5-10 to synchronized heifers (n = 7 heifers per bull; total 42 heifers). Conceptus recovery rate on d 15 was higher in HF (59.4%,) versus LF (45.0%). Mean length of recovered conceptuses for HF bulls was not affected by fertility status. In conclusion, while differences in field fertility among AI sires used in this study were not reflected in fertilization rate, differences in embryo quality were apparent as early as d 7. These differences likely contributed to the higher proportion of conceptuses surviving to d 15 in HF bulls.
尽管经过常规精液质量实验室测试，用于人工授精 (AI) 的公牛在田间生育力方面仍存在显著差异。本研究的目的是确定 AI 公牛的亚生育力是由于精子向受精部位的输送问题、受精失败、还是早期胚胎或胚胎发育失败引起的。在实验 1 中，根据至少 500 次授精的调整生育评分，从全国 AI 公牛群体中选择荷斯坦弗里生公牛（3 头高生育力，HF，和 3 头低生育力，LF）（HF：+4.37%和 LF：-12.7%；平均值=0%）。根据 AI 时估计的卵泡数量对肉牛小母牛进行分组，并使用 HF 或 LF 公牛的精液进行授精（每头公牛 3-4 头小母牛；共 19 头小母牛）。7 天后屠宰后，计数黄体数并冲洗子宫。根据发育阶段对回收结构（卵母细胞/胚胎）进行分类，并使用 4'，6-二脒基-2-苯基吲哚进行染色，以评估精子数量和辅助精子。总回收率（回收结构总数/总黄体数）为 52.6%，各组间无差异。每个受体回收的胚胎平均数（±标准误差）分别为 HF 和 LF 组的 8.7±5.2 和 9.4±5.5。各组间回收结构的总受精率无差异。然而，更多的胚胎处于发育的后期阶段（所有囊胚阶段合并），这反映在 HF 公牛的胚胎第 7 天的平均胚胎细胞数更大。来自 HF 公牛的胚胎的辅助精子数量多于 LF 公牛的胚胎。实验 2 的目的是评估公牛生育力对牛胚胎存活至第 15 天的影响。使用来自相同 HF（n=3）和 LF（n=3）公牛的精液在体外生产第 7 天的囊胚，并将其分组为 5-10 个胚胎转移到同步化的小母牛（每头公牛 7 头小母牛；共 42 头小母牛）。HF（59.4%）组的第 15 天回收的胚胎回收率高于 LF（45.0%）组。HF 公牛回收的胚胎长度不受生育力状态的影响。总之，尽管本研究中用于 AI 的公牛在田间生育力方面存在差异，但在第 7 天就已经明显出现胚胎质量的差异。这些差异可能导致 HF 公牛中更多的胚胎存活至第 15 天。
