Blood plasma concentrations of metabolic hormones and glucose during extended lactation in grazing cows or cows fed a total mixed ration |
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Authors: | Delany K K Macmillan K L Grainger C Thomson P C Blache D Nicholas K R Auldist M J |
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Affiliation: | *CRC for Innovative Dairy Products, Department of Zoology, University of Melbourne, VIC 3010, Australia;†Department of Veterinary Science, University of Melbourne, Werribee VIC 3030, Australia;‡Future Farming Systems Research Division, Department of Primary Industries, Ellinbank VIC 3821, Australia;§Faculty of Veterinary Science, University of Sydney, Camden NSW 2570, Australia;#School of Animal Biology, University of Western Australia, Crawley WA 6009, Australia |
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Abstract: | An experiment was conducted to measure the effect of diet on circulating concentrations of metabolic hormones and metabolites in cows undergoing extended lactations. Two groups of 6 Holstein-Friesian cows managed for lactations of 670 d were used in the experiment. One group was fully fed on a total mixed ration (TMR), whereas the other group grazed fresh pasture supplemented with grain (P+G). On 7 occasions between 332 and 612 d in milk, concentrations of metabolic hormones and glucose were measured in the blood plasma of each cow. Cows fed TMR gained more weight and body condition than P+G cows, but did not produce more milk during the study period. Only 3 of the TMR cows continued to lactate until 612 d in milk compared with all 6 of the P+G cows. Blood plasma from cows fed TMR had higher concentrations of glucose, insulin, glucagon, insulin-like growth factor 1, and leptin, but lower concentrations of growth hormone, than that from P+G cows. These changes were consistent with the preferential deposition of energy into adipose tissue at the expense of milk production and presumably were induced by a diet that provided precursors for gluconeogenesis that were in excess of the requirements for maintenance and prevailing milk production. The mechanism responsible for some TMR cows putting on excess weight and reducing or ceasing milk production is uncertain, but this observation has important implications for the nutritional management of cows in extended lactation programs. |
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Keywords: | pasture hormone total mixed ration energy |
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