Departamento de Reproducción Animal Conservación de Recursos Zoogenéticos, INIA, 28040 Madrid, Spain.
J Dairy Sci. 2012 Jul;95(7):3865-76. doi: 10.3168/jds.2011-5270.
The aim of this study was to examine the direct effect of lactation on the ability of the reproductive tract of postpartum dairy cows to support early embryo development. Twenty-one primiparous Holstein heifers were used. Immediately after calving, half of the cows were dried off (i.e., never milked), and the other half entered the milking herd and were milked twice daily. Jugular blood samples were taken twice per week from 15 d before calving to approximately 100 d postpartum to measure nonesterified fatty acids, β-hydroxybutyrate, glucose, insulin, and insulin-like growth factor-I. At the same time, body weight and body condition score were recorded for each cow. At approximately 60 d postpartum (experiment 1), approximately 65 two- to four-cell embryos, produced by in vitro maturation and fertilization, were endoscopically transferred to the oviduct ipsilateral to the corpus luteum of all cows on d 2 of the estrous cycle. Five days later (d 7), the oviduct and uterus were flushed nonsurgically and the number of embryos developing to the blastocyst stage was recorded. At approximately 90 d postpartum (experiment 2), the estrous cycles of the same cows were resynchronized and 15 to 20 in vitro-produced blastocysts were transferred to the uterus of each recipient on d 7. All cows were slaughtered on d 14 to assess embryo survival and dimensions. Body weight and body condition score were significantly different between groups for the entire postpartum period of the study. Concentrations of nonesterified fatty acids and β-hydroxybutyrate were higher and concentrations of glucose, insulin, and insulin-like growth factor-I were lower in lactating compared with nonlactating cows. Embryo recovery rates from lactating and dry cows were similar. In experiment 1, fewer embryos developed to the blastocyst stage in the lactating cows compared with the nonlactating cows. In experiment 2, embryo survival and conceptus dimensions were not different between lactating and nonlactating cows. In conclusion, the data indicate that the reproductive tract of the lactating dairy cow is compromised in its ability to support early embryo development compared with that of matched dry cows and this may contribute to early embryo mortality observed in such animals.
本研究旨在探讨泌乳对产后奶牛生殖道支持早期胚胎发育能力的直接影响。选择 21 头初产荷斯坦黑白花奶牛。产后立即，一半奶牛停乳（即不再挤奶），另一半奶牛进入挤奶群，每天挤奶两次。从产前 15 天到产后约 100 天，每周采集两次颈静脉血样，以测量非酯化脂肪酸、β-羟丁酸、葡萄糖、胰岛素和胰岛素样生长因子-I。同时，记录每头奶牛的体重和体况评分。产后约 60 天（实验 1），在发情周期第 2 天，通过体外成熟和受精，将大约 65 个 2-4 细胞胚胎经内窥镜转移到所有奶牛黄体同侧的输卵管。5 天后（第 7 天），对输卵管和子宫进行非手术冲洗，记录胚胎发育至囊胚阶段的数量。产后约 90 天（实验 2），对同一批奶牛的发情周期进行同步化处理，并在第 7 天将 15-20 个体外生产的囊胚移植到每个受体的子宫内。所有奶牛于第 14 天屠宰，以评估胚胎存活率和形态。在整个研究的产后期间，两组奶牛的体重和体况评分差异显著。与非泌乳奶牛相比，泌乳奶牛的非酯化脂肪酸和β-羟丁酸浓度较高，葡萄糖、胰岛素和胰岛素样生长因子-I 浓度较低。从泌乳和干奶牛中回收胚胎的效率相似。在实验 1 中，与非泌乳奶牛相比，泌乳奶牛的胚胎发育到囊胚阶段的比例较低。在实验 2 中，泌乳和非泌乳奶牛的胚胎存活率和胚胎形态没有差异。综上所述，数据表明，与匹配的干奶牛相比，泌乳奶牛的生殖道支持早期胚胎发育的能力受损，这可能导致此类动物早期胚胎死亡率升高。
