Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, QC, Canada J1K 2R1.
J Dairy Sci. 2011 Oct;94(10):4922-36. doi: 10.3168/jds.2010-4116.
The objective of this study was to evaluate the effect of shortening the dry period on the mammary gland and the hormonal regulation of its functions. Holstein cows (n = 18) were assigned to a short dry period (SDP; 35 d; n = 9) or a conventional dry period (CDP; 65 d; n = 9). All cows were fed the same diets, with the exception that, during the dry period, the SDP cows received only the pre-calving diet for 35 d, whereas the CDP cows were fed a high-fiber diet from 65 to 28 d before calving and then received the same pre-calving diet as the SDP cows. Mammary gland functional capacity was evaluated at 70 days in milk, and mammary biopsies were taken in early and midlactation. Dry period length averaged 64.3 ± 1.1 and 31.9 ± 1.0 d for the CDP and SDP cows, respectively. The SDP cows had a lower milk yield and a lower energy-corrected milk yield compared with the CDP cows. The SDP cows also had a lower dry matter intake from wk 5 to 20 of lactation and tended to have lower plasma concentrations of β-hydroxybutyrate from wk 1 to 4. Prepartum serum progesterone and estradiol concentrations were unaffected by the dry period management. Serum growth hormone concentrations and milking-induced prolactin release were similar in both groups. However, during the period when the CDP cows were dry but the SDP cows were still being milked (wk -9 to -6), serum prolactin concentrations were higher in the SDP cows than in the CDP cows. The SDP cows had a lower milk BSA content than the CDP cows after the dry period and similar milk lactose concentrations, suggesting that their mammary tight junctions were closed following parturition and, therefore, that the later stage of their lactogenesis was not impaired by SDP management. In early and midlactation, mammary cell apoptosis and proliferation rates as well as mammary expression of genes involved in the function of this tissue were unaffected by the dry period management strategy. For cows in their second lactation, mammary gland functional capacity at 70 d in milk tended to be lower in the SDP cows. In conclusion, even though SDP management decreased milk production during the subsequent lactation, it did not affect mammary cell activity. Although direct evidence is still lacking, decreased mammary cell growth during the dry period is likely responsible for this negative effect. The higher prolactin concentrations in lactating cows during late gestation could be involved in this effect. More research is needed to test these hypotheses.
本研究旨在评估缩短干奶期对乳腺和激素调节功能的影响。选择荷斯坦奶牛（n=18）分为短干奶期组（SDP；35d；n=9）和常规干奶期组（CDP；65d；n=9）。所有奶牛均采用相同的日粮，不同之处在于 SDP 组奶牛在干奶期仅饲喂产前日粮 35d，而 CDP 组奶牛在产前 65d 至 28d 期间饲喂高纤维日粮，然后饲喂与 SDP 组奶牛相同的产前日粮。在产后 70d 时评估乳腺功能容量，并在泌乳早期和中期采集乳腺活检。CDP 和 SDP 组奶牛的干奶期平均为 64.3±1.1d 和 31.9±1.0d。与 CDP 组相比，SDP 组奶牛产奶量和校正能量奶产量较低。SDP 组奶牛在泌乳第 5 周至 20 周的干物质采食量也较低，并且从第 1 周到第 4 周的β-羟丁酸的血浆浓度呈下降趋势。产前血清孕酮和雌二醇浓度不受干奶期管理的影响。两组的血清生长激素浓度和挤奶诱导的催乳素释放相似。然而，在 CDP 组奶牛干奶而 SDP 组奶牛仍在泌乳期间（-9 周至-6 周），SDP 组奶牛的血清催乳素浓度高于 CDP 组。与 CDP 组相比，SDP 组奶牛在干奶期后的牛奶 BSA 含量较低，而乳糖浓度相似，这表明它们的乳腺紧密连接在分娩后关闭，因此，SDP 管理不会损害其泌乳后期的功能。在泌乳早期和中期，乳腺细胞凋亡和增殖率以及参与乳腺组织功能的基因的乳腺表达不受干奶期管理策略的影响。对于第二次泌乳的奶牛，产后 70d 的乳腺功能容量在 SDP 组奶牛中趋于较低。总之，尽管 SDP 管理减少了后续泌乳期间的产奶量，但并未影响乳腺细胞的活性。尽管仍然缺乏直接证据，但在干奶期乳腺细胞生长减少可能是这种负效应的原因。在妊娠晚期泌乳奶牛中较高的催乳素浓度可能与这种效应有关。需要进一步的研究来检验这些假设。
