Manipulation of Lactation Persistency to Achieve Extended Lactation in Dairy Cows

Sorensen, Annette (2000) Manipulation of Lactation Persistency to Achieve Extended Lactation in Dairy Cows. PhD thesis, University of Glasgow.

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This thesis investigated management practices that might be used to manipulate lactation persistency to achieve extended lactation in dairy cows. Factors under investigation were milking frequency, nutrition and calving season. Increased milking frequency resulted in an increased milk yield by as much as 50% and significantly improved lactation persistency. Nutrition and calving season increased milk yield but only had short term effects on lactation persistency. This suggests that while milking frequency has a continuing stimulatory effect on the mammary cell population, nutrition and calving season might have an initial stimulatory effect to adapt to a higher level of milk production but no long lasting effects. The most consistent and significant predictor of lactation persistency was peak milk yield, which was negatively correlated with lactation persistency (-0.68). Fertility parameters and endocrine profiles were also investigated during extended lactation. No evidence was found to suggest that re-breeding at a later stage of lactation was any easier or worse than during early lactation. Extended lactation did not compromise future reproductive success. It is inevitable that good reproductive management will remain an essential part of any extended lactation strategy. A persistent lactation was positively correlated with changes in GH (0.14) and negatively with changes in insulin (-0.29), suggesting that nutrient partitioning is important in maintaining lactation persistency. This effect might be indirect since nutrient partitioning affects milk yield. The last part of the study determined whether the same treatment used to manipulate lactation persistency also affected milk protein quality. Both frequent milking and supplementary feeding increased casein number, indicative of good processing quality. In combination these were able to completely maintain casein number through lactation. The mechanism underlying the effect of frequent milking on milk protein quality was shown to be bi-factorial, reduced storage time of milk within the udder together with decreased involution (and thus better integrity of mammary tight junctions) both contributing to reduced casein proteolysis by components of the plasmin system. This thesis has shown that it is possible to manipulate lactation persistency to extend lactation in dairy cows but careful management is required.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Chris Knight
Keywords: Animal sciences
Date of Award: 2000
Depositing User: Enlighten Team
Unique ID: glathesis:2000-76011
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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