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Title: Dietary effects on milk protein in dairy cows
Author: Wood, Bethan Louise
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1990
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The nutritional and non-nutritional factors influencing dairy cow milk production were reviewed, with particular attention to the effects of diet. Three experiments were undertaken to study further the effects of diet on milk production, especially milk protein content and yield. The initial experiment examined the effects of three complete, but differing HE diets, pre and post-partum, on animal performance. The higher HE diets significantly increased TDHI, and animals offered these diets showed a lower weight loss and an earlier peak milk yield. No significant effects on milk fat or lactose contents were observed, but milk protein content was consistently higher in the higher energy fed cows. Milk casein contents were depressed from normal lactational values, but were higher in the higher energy fed cows. The conclusions from this trial were that the costs of the higher energy diets outweighed the small increases found in milk yield and constituents. Experiment 2 examined the effects of a high crude protein concentrate, fed at different stages of lactation, on milk production. The substitution rate of silage with concentrates was lower and silage DMI was significantly higher in the high protein fed cows. Milk analysis results (with the exception of the casein and NPN results) were adjusted by covariance. Milk yield was significantly higher in the high protein fed animals up to 18 weeks of lactation, with no significant differences being recorded in milk fat or lactose content. Significant increases were found in NPN content in the high protein diets, but with no effect on milk casein content. The conclusion of this work was that with a good quality silage, including a low degradability animal protein in the supplement had no beneficial effect on milk production. The final experiment was a short-term changeover trial examining the effects of two energy sources (starch and sugar) at two crude protein levels on milk production. There were no significant differences in forage intake. Milk results (excepting casein and NPN) were adjusted by covariance. Average milk yield and constituent contents were higher with the starch diets although the sugar diets showed a greater response in milk yield to increased dietary protein. Milk casein content was unaffected by the diets, but NPN content was significantly higher in the starch diet at the higher protein level. The conclusions from these experiments are that future work should be centred around: dietary effects on milk protein constituents, and development of an accurate method for calibrating milk analysis machines for milk casein; more long term trials should be used to examine total lactational changes and effects of cow condition manipulation prepartum on body reserves utilisation, and, trials should be designed to examine the effect of feeding frequency of sugar based supplements on forage intake.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available