Henry J Leese

Effect of Elevated Systemic Concentrations of Ammonia and Urea on the Metabolite and Ionic Composition of Oviductal Fluid in Cattle

Abstract High dietary protein leads to elevated systemic concentrations of ammonia and urea, and these, in turn, have been associated with reduced fertility in cattle. The effect of elevating systemic concentrations of ammonia and urea on the concentrations of electrolytes and nonelectrolytes in bovine oviductal fluid were studied using estrus-synchronized, nulliparous heifers (n = 25). Heifers were randomly assigned to 1 of 3 treatments consisting of jugular vein infusion with either ammonium chloride (n = 8), urea (n = 8), or saline (n = 9). Oviducts were catheterized, and fluid was recovered over a 3-h period on either Day 2 or 8 of the estrous cycle. No difference (P > 0.05) was found in the concentrations of any electrolyte or nonelectrolyte between oviducts ipsi- or contralateral to the corpus luteum. Plasma and oviductal concentrations of urea were increased by infusion with urea (P < 0.001) and ammonium chloride (P < 0.05) but not by saline (P > 0.05). Plasma and oviductal concentrations of ammonia were elevated by infusion with ammonium chloride (P < 0.001) but not by infusion with urea or saline (P > 0.05). No effect (P > 0.05) of treatment was found on oviductal or plasma concentrations of glucose, lactate, magnesium, potassium, or sodium or on plasma concentrations of insulin or progesterone. The concentration of calcium in oviductal fluid was reduced by urea infusion and was negatively associated with systemic and oviductal concentrations of urea. Oviductal concentrations of sodium were higher on Day 8 than on Day 2 (P < 0.05). No effect of sample day was found on any of the other electrolytes or nonelectrolytes measured (P > 0.05). Elevated systemic concentrations of ammonia and urea are unlikely to reduce embryo survival through disruptions in the oviductal environment.

Amino acid metabolism of preimplantation bovine embryos cultured with bovine serum albumin or polyvinyl alcohol

Bovine serum albumin (BSA) is an embryotrophic macromolecule used in embryo culture media, which is commonly replaced with synthetic compounds, such as polyvinyl alcohol (PVA). This study compared the effect of BSA and PVA on the development, blastocyst cell number and amino acid metabolism of preimplantation bovine embryos in vitro. Embryos were produced by in vitro maturation and fertilization of immature oocytes from abattoir-derived ovaries. Zygotes were cultured in synthetic oviduct fluid with either 4 mg/ml BSA (SOFaaBSA) or 1 mg/ml PVA (SOFaaPVA) in microdrops with a mineral oil overlay at 39 degrees C under a 5% O2/5% CO2/90% N2 atmosphere. Blastocyst rate and cell numbers were determined after 123 h of culture. In parallel, single expanding blastocysts grown in either medium were incubated in microdrops for 12 h. Amino acid profile of spent drops was determined by high performance liquid chromatography. Replacing BSA with PVA depressed blastocyst rate and cell numbers, and led to quantitative and qualitative differences in amino acid appearance, disappearance and turnover. These differences could partly be due to an increase in free intracellular amino acid concentration in SOFaaBSA embryos derived from hydrolysis of endocytosed BSA, and argue against the inclusion of PVA in bovine embryo culture media.

Effect of timing of urea feeding on the yield and quality of embryos in lactating dairy cows

High protein diets, which lead to excess production of nonprotein nitrogen such as ammonia and urea, have been associated with reduced fertility in dairy cows. In this study we test the hypothesis that diets containing high levels of quickly degradable urea nitrogen (QDN) compromise embryo development. Lactating dairy cows were fed mixed silage and concentrates twice daily. At 60 days postpartum, a synchronized estrus was induced and the cows were subsequently superovulated and inseminated using a standard protocol. On Day 7 after insemination, the uteri were flushed and embryos retrieved. At the start of treatment, cows were randomly allocated into three nutritional groups: control (CONT, n = 8), long (L-) QDN (n = 8) and short (S-) QDN (n = 9). The L-QDN cows were fed a supplement of urea from 10 days before insemination, and the S-QDN cows were fed the supplement from insemination until embryo collection. Both L- and S-QDN diets produced significant increases in plasma ammonia and urea 3 h post-feeding. The S-QDN but not the L-QDN diet was associated with a significant reduction in embryo yield. Embryo quality was also significantly reduced in the S-QDN cows. This study indicates that there is no deleterious effect on the yield and quality of embryos recovered 7 days after breeding when QDN feeding is initiated during the previous midluteal phase. However, introduction of a similar diet 10 days later, at the time of insemination, was deleterious. We suggest that QDN is toxic to embryos but cows can adjust within 10 days.