Investigation of Factors Influencing Lactation Persistency in the Goat

Brown, Joanna R (1996) Investigation of Factors Influencing Lactation Persistency in the Goat. PhD thesis, University of Glasgow.

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This thesis examines some of the factors which play a role in determining lactation persistency in the goat with the overall aim of improving persistency. The plasticity of mammary gland growth during pregnancy and lactation was investigated by treatments of growth hormone and stimulation of compensatory growth. Cell activities and differentiation could be altered but the effects were dependent on the physiological state of the animal with longer term responses in milk production associated with treatments given during late gestation. The endocrine influence of prolactin and oxytocin were examined by attempting to elevate circulating prolactin by administering perphenazine and by giving exogenous oxytocin during lactation. The former treatment was successful in the short-term when given by intravenous infusion but oral and injected doses given during lactation were not. Oxytocin had a small and positive effect on persistency, most marked when combined with reduced milking frequency in late lactation. The effects of once- and thrice-daily milking, suckling and continuous drainage of milk from the mammary gland for the first six weeks of lactation, followed by routine milking for the remainder of lactation were examined in conjunction with the influence of parity on the responses obtained. Drainage proved ineffective in increasing yields or improving persistency. Suckling and thrice-daily milking enhanced milk yields in the short-term but no long-term alteration of persistency was seen. Once-daily milking was tolerated well by multiparous but not primiparous animals, but there was a trend of improved persistency with this treatment, regardless of parity. This may reflect alterations in the partitioning of milk stored within the udder but measurements made 5 hours post-milking did not show any differences between these and contralateral thrice-daily milked glands. Finally the effectiveness of caseins (milk proteins) in providing a measurement of lactation persistency by indirect measurement of cellular involution was studied. It was found that the production of caseins varied over lactation, and that 7-casein production was highly (negatively) correlated with milk production. However, the best measure of cellular function was to measure milk yield itself. In conclusion, the timing of treatments can be crucial in determining the response obtained and alteration of lactation persistency was very difficult to achieve. The most promising route suggested by this work is reducing milking frequency during established lactation, in combination with early lactation treatments to enhance yields.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Chris Knight
Keywords: Animal sciences
Date of Award: 1996
Depositing User: Enlighten Team
Unique ID: glathesis:1996-75700
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Dec 2019 09:15
Last Modified: 19 Dec 2019 09:15

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