Date of Award
Master of Science
Patrick J. Gunn
The effect of excess dietary protein supplementation on ovarian function of beef cows consuming low quality forage was investigated. In a pair of studies, non-pregnant, non-lactating beef cows were supplemented with excess dietary protein along with ad libitum access to chopped corn stalks. In the first study, the objective was to determine the effect of feeding excess metabolizable protein (MP) from feedstuffs differing in rumen degradability on ovarian parameters. Cows were supplemented with either a moderately undegradable protein (corn gluten meal; CGM) or low-undegradable protein (soybean meal; SBM) based supplement, formulated to supply 150% of NRC MP requirements for 58 days (d). Cows supplemented with CGM experienced greater dominant follicle growth post-dominance, larger follicles at spontaneous luteolysis, shorter duration of proestrus, and larger ovulatory follicles than SBM-treated cows. Peak estradiol production and corpus luteum volume did not differ due to treatment, but within the CGM treatment, cows tended to have lesser progesterone concentrations 7 d post-estrus compared to cows consuming the SBM supplement. Circulating plasma urea N (PUN) concentrations were elevated after supplementation in both treatment groups; yet no differences between treatments existed at ovulation. Total circulating plasma amino acid (AA) concentrations were not different between treatments after supplementation, but individual AA concentrations were shifted based on degradability of the protein supplement.
In order to determine if enhanced ovarian parameters observed in the first study was mediated by amount of undegradable protein, a second study was conducted offering excess RUP at two inclusion levels. In the second study, cows were supplemented once daily with a moderately rumen undegradable protein (RUP) supplement, consisting primarily of corn gluten meal (62% RUP), at either 125% or 150% of NRC MP requirements for 60 d. Cows exposed to 150% MP had larger ovulatory follicles and greater antral follicle counts than cows in the 125% MP treatment. Estradiol and progesterone concentrations did not differ due to treatment; however, CL volume was greater in the 150% treatment group. Circulating urea N concentrations were elevated in both treatments at ovulation when compared to study initiation; however, PUN concentrations from cows consuming 150% MP exceeded concentrations of cows consuming 125% MP supplement after onset of the ovulatory follicle wave on interest. No differences in total circulating plasma AA concentrations existed between treatments before or after excess MP supplementation; yet, branched-chain AA were greater as a percent of total AA in cows offered 150% MP compared to 125% MP.
In summary, the data from these two studies indicate that degradability of feedstuffs, as well as inclusion, differentially affects ovarian functions of beef cows consuming a base diet of low quality forage. However, both studies demonstrate that excess undegradable protein fed to 150% of NRC MP requirements enhances ovarian function when compared to excess RDP or RUP supplementation at 125% MP. Therefore, we conclude that ovarian function of beef cows maintained on low quality forage can be enhanced by including excess protein from a moderately undegradable protein source at 150% of MP requirements and further research is warranted to translate effects to overall fertility.
Taylor Clair Geppert
Geppert, Taylor Clair, "Effects of excess dietary protein on ovarian function of beef cows" (2015). Graduate Theses and Dissertations. 14657.