UVM Theses and Dissertations
Format:
Print
Author:
Wall, Emma
Dept./Program:
Animal Sciences
Year:
2009
Degree:
PhD
Abstract:
Frequent milking of dairy cows during early lactation stimulates an increase in milk production that persists through the remainder of lactation. We hypothesized that the milk yield response is regulated locally within the mammary gland. Cows were assigned at parturition to unilateral frequent milking (UFM; twice daily milking (2X) of the left udder half, four-times daily milking (4X) of the right udder half) for days 1 to 21 of lactation. After treatment, cows were milked 2X for the remainder of lactation. During UFM, 4X udder halves produced 3.9 ± 0.7 kg/d more milk than 2X udder halves. Upon cessation of treatment, milk production from the 4X udder halves decreased transiently, then restabilized to 1.8 ± 0.5 kg/d more milk than 2X udder halves for the remainder of lactation. In addition, the milk yield response that we observed was consistent with previous reports in which 4X milking was applied to groups of cows, rather than half-udders.
After validating a half-udder model for use in subsequent experiments, we hypothesized that the duration of frequent milking during early lactation could be decreased and still stimulate a persistent increase in milk yield. Cows were assigned at parturition to UFM on d 1 to 14 (UFM-1-14) or 7 to 21 (UFM-7-21) of lactation. For both treatments, the 4X udder halves produced more milk than the 2X udder halves during UFM. In both treatments, 4X udder halves produced more milk than 2X udder halves for the remainder of lactation; however, the difference was significant for UFM-7-21 cows only. Therefore, frequent milking for a 2-wk interval during early lactation elicited a persistent increase in milk production. To gain insight into the mechanisms underlying the milk yield response, and to identify genes associated with the acute transient response of the mammary gland to milk removal vs. those associated with the sustained mammary response to frequent milking treatment, we obtained mammary biopsies from UFM cows on d 5 of lactation.
Biopsies were obtained either immediately after the 4X udder half was milked but 3.5 h after the 2X udder half had last been milked, or 2.5 h after both udder halves had last been milked. Mammary cell proliferation and apoptosis were not affected by milk removal or by UFM; however, expression of genes involved in the insulin-like growth factor (IGF) signaling axis were acutely and transiently responsive to milk removal. In addition, using Affyrnetrix GeneChip® Bovine Genome Arrays, we determined that the expression of 72 genes was acutely and transiently regulated by removal of milk from the mammary gland, whereas expression of six genes was regulated by frequent milking treatment. To gain insight into the mechanisms underlying the 3 phases of the milk yield response (increased milk yield during frequent milking, transiently decreased upon cessation of frequent milking, and persistently increased milk yield thereafter), mammary biopsies were obtained from UFM cows on d 21, 23, and 40 of lactation.
Mammary cell proliferation and apoptosis were not affected by UFM. Using Affyrnetrix GeneChip® Bovine Genome Arrays, we identified a cluster of 15 genes that were coordinately regulated in response to UFM, and the temporal pattern of differential gene expression was highly correlated with mammary cell apoptosis. Nine of the genes in the cluster were still differentially expressed on d 40 of lactation, indicating that they are involved in the persistent milk yield response. Several of these genes have been associated with mammary development, differentiation and remodeling; any of which may be functionally related to the increase in milk yield. The results of this investigation indicate that a coordinated transcriptional response underlies the increase in milk yield elicited by frequent milking during early lactation. Furthermore, the transcriptional "signature" that we have discovered may be a marker for the autocrine regulation of milk production and cellular apoptosis in the bovine mammary gland.
After validating a half-udder model for use in subsequent experiments, we hypothesized that the duration of frequent milking during early lactation could be decreased and still stimulate a persistent increase in milk yield. Cows were assigned at parturition to UFM on d 1 to 14 (UFM-1-14) or 7 to 21 (UFM-7-21) of lactation. For both treatments, the 4X udder halves produced more milk than the 2X udder halves during UFM. In both treatments, 4X udder halves produced more milk than 2X udder halves for the remainder of lactation; however, the difference was significant for UFM-7-21 cows only. Therefore, frequent milking for a 2-wk interval during early lactation elicited a persistent increase in milk production. To gain insight into the mechanisms underlying the milk yield response, and to identify genes associated with the acute transient response of the mammary gland to milk removal vs. those associated with the sustained mammary response to frequent milking treatment, we obtained mammary biopsies from UFM cows on d 5 of lactation.
Biopsies were obtained either immediately after the 4X udder half was milked but 3.5 h after the 2X udder half had last been milked, or 2.5 h after both udder halves had last been milked. Mammary cell proliferation and apoptosis were not affected by milk removal or by UFM; however, expression of genes involved in the insulin-like growth factor (IGF) signaling axis were acutely and transiently responsive to milk removal. In addition, using Affyrnetrix GeneChip® Bovine Genome Arrays, we determined that the expression of 72 genes was acutely and transiently regulated by removal of milk from the mammary gland, whereas expression of six genes was regulated by frequent milking treatment. To gain insight into the mechanisms underlying the 3 phases of the milk yield response (increased milk yield during frequent milking, transiently decreased upon cessation of frequent milking, and persistently increased milk yield thereafter), mammary biopsies were obtained from UFM cows on d 21, 23, and 40 of lactation.
Mammary cell proliferation and apoptosis were not affected by UFM. Using Affyrnetrix GeneChip® Bovine Genome Arrays, we identified a cluster of 15 genes that were coordinately regulated in response to UFM, and the temporal pattern of differential gene expression was highly correlated with mammary cell apoptosis. Nine of the genes in the cluster were still differentially expressed on d 40 of lactation, indicating that they are involved in the persistent milk yield response. Several of these genes have been associated with mammary development, differentiation and remodeling; any of which may be functionally related to the increase in milk yield. The results of this investigation indicate that a coordinated transcriptional response underlies the increase in milk yield elicited by frequent milking during early lactation. Furthermore, the transcriptional "signature" that we have discovered may be a marker for the autocrine regulation of milk production and cellular apoptosis in the bovine mammary gland.