Location: Reproduction ResearchTitle: Removal of ruminal contents followed by restricted feeding does not affect the frequency of luteinizing-hormone pulses in steers Author
|Looper, Michael - Oklahoma Agriculture Experiment Station|
|Ojeda, Alejandro - Oklahoma Agriculture Experiment Station|
|Vizcarra, Jorge - Oklahoma Agriculture Experiment Station|
|Wettemann, Robert - Oklahoma Agriculture Experiment Station|
Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2015
Publication Date: 8/1/2015
Citation: Lents, C.A., Looper, M.L., Ojeda, A.J., Vizcarra, J.A., Wettemann, R.P. 2015. Removal of ruminal contents followed by restricted feeding does not affect the frequency of luteinizing-hormone pulses in steers. The Professional Animal Scientist. 31:349-353.
Interpretive Summary: Reproductive function in cattle is dependent upon the release of reproductive hormones from the pituitary gland. Secretion of these hormones is impacted by metabolism, but the mechanisms behind this regulation remain poorly understood. To address this, scientists experimentally controlled the amount of food in the stomach of cattle while taking frequent blood samples to measure the secretion of metabolic and reproductive hormones. They determined that secretion of luteinizing hormone, a key reproductive hormone, was altered by eating a meal but the amount eaten did not affect the response. This establishes an animal model that will allow scientists to more fully investigate how energy balance and nutrient absorption affect reproductive function in cattle; thereby leading to new strategies to maximize fertility of beef cows.
Technical Abstract: The objective of this study was to determine the effects of removal of ruminal contents and reduced nutrient intake on concentrations of LH in serum of beef cattle. Gonadectomized, male, Angus x Hereford cattle (steers, 402 ± 17 kg) with rumen cannulae were randomly assigned to treatment. Control (CON; n = 4) animals had ruminal contents completely removed and immediately replaced whereas restricted (RST; n = 4) animals had ruminal contents completely removed and only 15% (5 liters) of rumen contents replaced. Beginning at 1600 h on d 0, CON steers were fed 9 kg of prairie hay and 1 kg of a grain supplement each day, whereas RST steers were fed 1.8 kg of prairie hay daily. Blood samples were collected twice daily for determination of plasma concentrations of glucose, nonesterified fatty acids (NEFA), and urea nitrogen (PUN). Serial blood samples were collected at 10 min intervals for 8 h on days -1, 0, 1 and 3 to determine serum concentrations of LH. Concentrations of glucose in plasma were not influenced by treatment or day, but concentrations of NEFA and PUN in plasma after d 0 were greater (P < 0.01) in RST steers than CON steers. Frequency of pulses of LH was not influenced by treatment, but concentrations of LH (p < 0.01) were greater on d -1 compared with after removal and replacement of ruminal contents on d 0 and 1. Amplitude of pulses of LH was greater on d -1 compared with d 1 and 3. It is concluded that secretion of LH of steers is resistant to rapid and severe changes in nutrient availability, but that emptying and refilling of the rumen can affect LH secretion in cattle.