Effect of Feeding Quickly Degradable Nitrogen on the Development of Ovarian Follicles in Lactating Dairy Cows

The objective of this study was to examine the effect of an excess intake of quickly degradable nitrogen (QDN) on ovarian follicle development. Twenty lactating dairy cows were fed mixed silage and concentrates twice daily. The control diet was a typical ration for high producing dairy cows in the United Kingdom (crude protein (CP)=17.5%; metabolizable energy (ME)=11.8 MJ/kg DM). The cows were randomly divided into two groups, control diet (control; n=10) and excess QDN diet (QDN; n=10). The QDN group was fed an additional 250 g of urea per cow per day; for 17 days. Ovaries were scanned daily using B-mode ultrasonography for 17 days. The excess QDN diet resulted in significantly elevated (P 0.05) plasma urea concentrations four days after starting urea feeding and these were maintained until the end of the experiment. The QDN treatment did not significantly affect (P 0.5) the number of small (≥0.5 cm diameter), medium to large follicles (0.5-1.4 cm diameter) and pre-ovulatory (1.5-2.3 cm diameter) follicles. The results of the current study has shown that feeding excess QDN, as urea, for 17 days has no effect on ovarian follicle development in lactating dairy cows.