UVM Theses and Dissertations
Format:
Print
Author:
Martinez, Diana G.
Dept./Program:
Animal Science
Year:
2005
Degree:
MS
Abstract:
In ruminants, intake of colostrum is crucial for the transfer of passive immunity to the newborn. During colostrum formation there is a large transfer of immunoglobulins, particularly IgG₁, from maternal circulation into colostrum. It has been suggested that this transfer is mediated by the up-regulation of FcRn, the IgG₁ receptor. Other components (vitamins, cytokines, and growth factors) are also highly concentrated in colostrum. Based on the mechanism of transfer of IgG₁ into colostrum, we hypothesized that vitamins are transferred from maternal circulation into colostrum by mammary epithelial receptors highly expressed during colostrum formation. We also investigated the effects of photoperiod (day-length) on colostrogenesis. Since prolactin (PRL) is involved in the regulation of colostrogenesis, and photoperiod affects PRL concentrations in plasma, we quantified the effects of two photoperiod treatments on colostrogenesis.
The first animal trial involved 12 multiparous pregnant Holstein cows. The cows were dried off at 62 days prepartum and were placed on photoperiod treatment: short qay photoperiod treatment (SD; 8h light: 16h dark; n=6), or long day photoperiod treatment (LD; 16h light: 8h dark; 11=6) for the rest of the pregnancy. After parturition all the cows were placed on ambient photoperiod. The second animal trial involved 12 pubertal heifers that were assigned to either SD (n=6), or LD (n=6) and were hormonally induced into lactation with estrogen and progesterone (E + P) treatment. Twice-daily milking was initiated 21d after the initial E+P injection and all the heifers were placed on LD. We quantified mRNA expression of the following candidate receptors: megalin (vitamin A, vitamin B₁₂), low density lipoprotein receptor (LDL-R) ({b-carotene), folate receptor (folic acid) and cubilin (vitamin B₁₂) during colostrogenesis. In addition, we determined concentrations of b-carotene, vitamin B₁₂ and folic acid in plasma and colostrum. Concentrations of IgG₁ in plasma and colostrum were used as colostrogenesis markers and concentrations of a-lactalbumin in plasma were used as a lactogenesis marker.
Immunohistochemistry was done to determine the location of megalin and LDL-R in bovine mammary tissue. Our results showed, in both experiments (cows and heifers), that megalin and LDL-R are located in mammary epithelial cells, and mRNA expression of those receptors increased during colostrogenesis. In addition, b-carotene concentrations in plasma declined during colostrogenesis whereas concentrations increased in colostrum. Expression of folate receptor and cubilin mRNA did not change during colostrogenesis, indicating that these receptors are not colostrogenesis associated. In addition, data from pregnant cows indicated that concentrations of vitamin B₁₂ and folic acid in plasma and mammary secretions did not change significantly during colostrogenesis. We did not detect an effect of photoperiod treatment on any measurements made, suggesting that day-length did not affect regulation of colostrogenesis. In conclusion, mRNA expression as well as immunohistochemical localization results for megalin and LDL-R are consistent with a possible role for these receptors in the transfer of vitamin A and b-carotene into colostrum. In contrast, results for folic acid and vitamin B₁₂ suggest that those vitamins do not share a similar mechanism of transfer into colostrum. Through a better understanding of the molecular mechanism of transport of colostral components, it may be possible to manipulate concentrations of immunoglobulins, vitamins and other bioactive components in colostrum, and therefore obtain a better quality of colostrum and improved calf health.
The first animal trial involved 12 multiparous pregnant Holstein cows. The cows were dried off at 62 days prepartum and were placed on photoperiod treatment: short qay photoperiod treatment (SD; 8h light: 16h dark; n=6), or long day photoperiod treatment (LD; 16h light: 8h dark; 11=6) for the rest of the pregnancy. After parturition all the cows were placed on ambient photoperiod. The second animal trial involved 12 pubertal heifers that were assigned to either SD (n=6), or LD (n=6) and were hormonally induced into lactation with estrogen and progesterone (E + P) treatment. Twice-daily milking was initiated 21d after the initial E+P injection and all the heifers were placed on LD. We quantified mRNA expression of the following candidate receptors: megalin (vitamin A, vitamin B₁₂), low density lipoprotein receptor (LDL-R) ({b-carotene), folate receptor (folic acid) and cubilin (vitamin B₁₂) during colostrogenesis. In addition, we determined concentrations of b-carotene, vitamin B₁₂ and folic acid in plasma and colostrum. Concentrations of IgG₁ in plasma and colostrum were used as colostrogenesis markers and concentrations of a-lactalbumin in plasma were used as a lactogenesis marker.
Immunohistochemistry was done to determine the location of megalin and LDL-R in bovine mammary tissue. Our results showed, in both experiments (cows and heifers), that megalin and LDL-R are located in mammary epithelial cells, and mRNA expression of those receptors increased during colostrogenesis. In addition, b-carotene concentrations in plasma declined during colostrogenesis whereas concentrations increased in colostrum. Expression of folate receptor and cubilin mRNA did not change during colostrogenesis, indicating that these receptors are not colostrogenesis associated. In addition, data from pregnant cows indicated that concentrations of vitamin B₁₂ and folic acid in plasma and mammary secretions did not change significantly during colostrogenesis. We did not detect an effect of photoperiod treatment on any measurements made, suggesting that day-length did not affect regulation of colostrogenesis. In conclusion, mRNA expression as well as immunohistochemical localization results for megalin and LDL-R are consistent with a possible role for these receptors in the transfer of vitamin A and b-carotene into colostrum. In contrast, results for folic acid and vitamin B₁₂ suggest that those vitamins do not share a similar mechanism of transfer into colostrum. Through a better understanding of the molecular mechanism of transport of colostral components, it may be possible to manipulate concentrations of immunoglobulins, vitamins and other bioactive components in colostrum, and therefore obtain a better quality of colostrum and improved calf health.