Effects of high protein diet intake, ammonia and urea concentrations on mid-luteal phase endometrial gene expression levels in post-partum dairy cows

Fertility in high producing dairy cows has been decreasing over decades. Elevated ammonia and urea levels in circulation and reproductive fluids due to high protein intake is one of the major contributory factors for decreasing fertility observed in dairy cows. The objectives of this study were to examine the effects of a) ammonia and urea, and b) high protein diet intake on the mRNA expression levels of mid-luteal phase endometrial candidate fertility genes in lactating dairy cows. In experiment I, the mRNA levels of endometrial candidate genes were measured using qRT-PCR after treating the endometrial tissues (100mg/well) with different concentrations of ammonium chloride (0, 75, 150, 300, 600 μM) or urea (0, 4, 8, 12, 16 mM), in-vitro. A high concentration of ammonium chloride (600 μM) or urea (16 mM) decreased (P<0.05) the expression levels of FGF2 and IGFBP1 genes when compared to the control. However, a mild concentration of ammonium chloride (150 μM) or urea (4 mM) increased (P<0.05) the expression levels of HSPA1A, IGFBP3, SERPINA14 and BCL2 genes. The expression levels of IGF1 and BAX genes were not affected (P>0.05) by any of the ammonium chloride or urea concentrations tested. In experiment II, the mRNA levels of the candidate genes were measured using qRT-PCR in the mid-luteal phase endometrium of post partum dairy cows fed with a high (17.3% DM) or a low (14.8% DM) protein diet. The mRNA levels of all genes tested except IL1A were not different (P>0.05) between the two groups. The mean number of small and large follicles, mean size of large follicles, mean size of CL, and the number of days to first ovulation were negatively affected by high protein diet intake. Milk analysis showed higher (P<0.05) MUN levels in the high protein group relative to that of low protein. Milk yield was not different (P>0.05) between the two groups. I conclude from this study that the deleterious effect of excess dietary protein on dairy cow fertility may be due to alterations in follicular and CL ...