Impact of bovine somatotropin administration beginning at day 70 of lactation on serum metabolites, milk constituents, and production in cows previously exposed to exogenous somatotropin

Ian J. Lean From the Veterinary Medical Teaching and Research Center, University of California, 18830 Road 112, Tulare, CA 93274 (Lean, Troutt, Galland, Weaver, Holmberg), the Department of Animal Science, Davis, CA 95616 (Baldwin), Department of Physiological Sciences, Davis CA 95616 (Bruss), the Department of Epidemiology and Preventive Medicine, Davis, CA 95616 (Farver), the Department of Animal Science, University of Sydney, Camden, NSW 2570, Australia (Lean), the Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln, Urbana, IL 61801 (Troutt), the College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5606 (Galland), and The Upjohn Co, Kalamazoo, MI 49001 (Rostami).

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R. Lee Baldwin From the Veterinary Medical Teaching and Research Center, University of California, 18830 Road 112, Tulare, CA 93274 (Lean, Troutt, Galland, Weaver, Holmberg), the Department of Animal Science, Davis, CA 95616 (Baldwin), Department of Physiological Sciences, Davis CA 95616 (Bruss), the Department of Epidemiology and Preventive Medicine, Davis, CA 95616 (Farver), the Department of Animal Science, University of Sydney, Camden, NSW 2570, Australia (Lean), the Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln, Urbana, IL 61801 (Troutt), the College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5606 (Galland), and The Upjohn Co, Kalamazoo, MI 49001 (Rostami).

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H. Fred Troutt From the Veterinary Medical Teaching and Research Center, University of California, 18830 Road 112, Tulare, CA 93274 (Lean, Troutt, Galland, Weaver, Holmberg), the Department of Animal Science, Davis, CA 95616 (Baldwin), Department of Physiological Sciences, Davis CA 95616 (Bruss), the Department of Epidemiology and Preventive Medicine, Davis, CA 95616 (Farver), the Department of Animal Science, University of Sydney, Camden, NSW 2570, Australia (Lean), the Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln, Urbana, IL 61801 (Troutt), the College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5606 (Galland), and The Upjohn Co, Kalamazoo, MI 49001 (Rostami).

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Michael L. Bruss From the Veterinary Medical Teaching and Research Center, University of California, 18830 Road 112, Tulare, CA 93274 (Lean, Troutt, Galland, Weaver, Holmberg), the Department of Animal Science, Davis, CA 95616 (Baldwin), Department of Physiological Sciences, Davis CA 95616 (Bruss), the Department of Epidemiology and Preventive Medicine, Davis, CA 95616 (Farver), the Department of Animal Science, University of Sydney, Camden, NSW 2570, Australia (Lean), the Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln, Urbana, IL 61801 (Troutt), the College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5606 (Galland), and The Upjohn Co, Kalamazoo, MI 49001 (Rostami).

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John C. Galland From the Veterinary Medical Teaching and Research Center, University of California, 18830 Road 112, Tulare, CA 93274 (Lean, Troutt, Galland, Weaver, Holmberg), the Department of Animal Science, Davis, CA 95616 (Baldwin), Department of Physiological Sciences, Davis CA 95616 (Bruss), the Department of Epidemiology and Preventive Medicine, Davis, CA 95616 (Farver), the Department of Animal Science, University of Sydney, Camden, NSW 2570, Australia (Lean), the Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln, Urbana, IL 61801 (Troutt), the College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5606 (Galland), and The Upjohn Co, Kalamazoo, MI 49001 (Rostami).

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Thomas B. Farver From the Veterinary Medical Teaching and Research Center, University of California, 18830 Road 112, Tulare, CA 93274 (Lean, Troutt, Galland, Weaver, Holmberg), the Department of Animal Science, Davis, CA 95616 (Baldwin), Department of Physiological Sciences, Davis CA 95616 (Bruss), the Department of Epidemiology and Preventive Medicine, Davis, CA 95616 (Farver), the Department of Animal Science, University of Sydney, Camden, NSW 2570, Australia (Lean), the Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln, Urbana, IL 61801 (Troutt), the College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5606 (Galland), and The Upjohn Co, Kalamazoo, MI 49001 (Rostami).

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Jeffrey Rostami From the Veterinary Medical Teaching and Research Center, University of California, 18830 Road 112, Tulare, CA 93274 (Lean, Troutt, Galland, Weaver, Holmberg), the Department of Animal Science, Davis, CA 95616 (Baldwin), Department of Physiological Sciences, Davis CA 95616 (Bruss), the Department of Epidemiology and Preventive Medicine, Davis, CA 95616 (Farver), the Department of Animal Science, University of Sydney, Camden, NSW 2570, Australia (Lean), the Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln, Urbana, IL 61801 (Troutt), the College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5606 (Galland), and The Upjohn Co, Kalamazoo, MI 49001 (Rostami).

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Leon D. Weaver From the Veterinary Medical Teaching and Research Center, University of California, 18830 Road 112, Tulare, CA 93274 (Lean, Troutt, Galland, Weaver, Holmberg), the Department of Animal Science, Davis, CA 95616 (Baldwin), Department of Physiological Sciences, Davis CA 95616 (Bruss), the Department of Epidemiology and Preventive Medicine, Davis, CA 95616 (Farver), the Department of Animal Science, University of Sydney, Camden, NSW 2570, Australia (Lean), the Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln, Urbana, IL 61801 (Troutt), the College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5606 (Galland), and The Upjohn Co, Kalamazoo, MI 49001 (Rostami).

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Charles A. Holmberg From the Veterinary Medical Teaching and Research Center, University of California, 18830 Road 112, Tulare, CA 93274 (Lean, Troutt, Galland, Weaver, Holmberg), the Department of Animal Science, Davis, CA 95616 (Baldwin), Department of Physiological Sciences, Davis CA 95616 (Bruss), the Department of Epidemiology and Preventive Medicine, Davis, CA 95616 (Farver), the Department of Animal Science, University of Sydney, Camden, NSW 2570, Australia (Lean), the Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, 2001 South Lincoln, Urbana, IL 61801 (Troutt), the College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506-5606 (Galland), and The Upjohn Co, Kalamazoo, MI 49001 (Rostami).

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Summary

Metabolic and production responses are reported for 72 cows treated with bovine somatotropin (bst) for 30 days starting at day 70 of lactation. Of these 72 cows, 48 had been exposed in the preceding lactation to long-term treatment with bst at 3 dosages and 24 (controls) had not been given bst. Approximately half of the cows in each group were parity-2 cows, the rest were older. Comparisons between groups were made separately for parity-2, and older cows.

Analyses, using pretreatment values of each variable as a covariate, indicated that older cows, but not parity-2 cows, significantly (P < 0.05) increased milk production during treatment. Parity-2 cows, however, had a significantly higher milk fat percentage than controls following treatment. Cows treated with 51.6 or 86 mg bst/d in both parity groups had significantly higher serum-free fatty acids than controls. Estimated net energy balances were significantly lower for older treated cows, but did not significantly differ from controls for parity-2 treated cows. Older cows in the 86 mg of bst/d group tended to have higher concentrations of blood glucose than did older control-group cows. Treatment with bst did not significantly increase serum ketone concentrations in any group of animals, and none of the cows developed clinical ketosis during this period.

Estimated net energy balance (eneb) during treatment was a significant (P < 0.05) covariate for free fatty acid concentrations in older cows and for milk fat percentage in parity-2 cows. Covariate adjusted analyses, using eneb during treatment as a covariate, indicated that lipolytic stimuli already acting may be enhanced by treatment with bst, but a negative energy balance was not a necessary precondition for free fatty acid concentrations to increase following somatotropin treatment. Similarly, milk fat percentages for parity-2 treated cows were significantly (P < 0.05) higher during treatment than controls when eneb during treatment was used as a covariate.

Increased milk fat concentrations in parity-2 treated cows were not associated with significant increases in the ratio of C18:C4-10 milk fatty acids, indicating that increased milk fat resulted from either an increase in incorporation of C18 fatty acids into milk fat coupled with an increase in de novo mammary synthesis of C4-10 milk fatty acids or an increase in C12-16 fatty acids that may arise either from increased tissue mobilization, from diet, or from de novo mammary synthesis.

Summary

Metabolic and production responses are reported for 72 cows treated with bovine somatotropin (bst) for 30 days starting at day 70 of lactation. Of these 72 cows, 48 had been exposed in the preceding lactation to long-term treatment with bst at 3 dosages and 24 (controls) had not been given bst. Approximately half of the cows in each group were parity-2 cows, the rest were older. Comparisons between groups were made separately for parity-2, and older cows.

Analyses, using pretreatment values of each variable as a covariate, indicated that older cows, but not parity-2 cows, significantly (P < 0.05) increased milk production during treatment. Parity-2 cows, however, had a significantly higher milk fat percentage than controls following treatment. Cows treated with 51.6 or 86 mg bst/d in both parity groups had significantly higher serum-free fatty acids than controls. Estimated net energy balances were significantly lower for older treated cows, but did not significantly differ from controls for parity-2 treated cows. Older cows in the 86 mg of bst/d group tended to have higher concentrations of blood glucose than did older control-group cows. Treatment with bst did not significantly increase serum ketone concentrations in any group of animals, and none of the cows developed clinical ketosis during this period.

Estimated net energy balance (eneb) during treatment was a significant (P < 0.05) covariate for free fatty acid concentrations in older cows and for milk fat percentage in parity-2 cows. Covariate adjusted analyses, using eneb during treatment as a covariate, indicated that lipolytic stimuli already acting may be enhanced by treatment with bst, but a negative energy balance was not a necessary precondition for free fatty acid concentrations to increase following somatotropin treatment. Similarly, milk fat percentages for parity-2 treated cows were significantly (P < 0.05) higher during treatment than controls when eneb during treatment was used as a covariate.

Increased milk fat concentrations in parity-2 treated cows were not associated with significant increases in the ratio of C18:C4-10 milk fatty acids, indicating that increased milk fat resulted from either an increase in incorporation of C18 fatty acids into milk fat coupled with an increase in de novo mammary synthesis of C4-10 milk fatty acids or an increase in C12-16 fatty acids that may arise either from increased tissue mobilization, from diet, or from de novo mammary synthesis.

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