Jugular Plasma Concentrations of Alpha Amino Nitrogen, Amino Acids, Urea Nitrogen, and Glucose During the Bovine Estrous Cycle

Abstract

Jugular plasma concentrations of alpha amino nitrogen, acidic and neutral amino acids, urea nitrogen, and glucose were measured during estrous cycles of 33 lactating cows. The estrous cycle was divided into four periods: proestrus (1 to 5 days before estrus), estrus, metestrus (1 to 3 days postestrus), and diestrus. Mean alpha amino nitrogen concentrations for the four periods were 4.85, 3.86, 4.06, and 4.53 mg/100ml. Acidic and neutral amino acids were assayed in samples drawn before and after the proestrus estrogen peak. Threonine, valine, methionine, isoleucine, and proline were all higher before than after the estrogen peak. Neither plasma urea nitrogen nor glucose concentrations varied significantly with different phases of the estrous cycle. However, the mean plasma glucose concentration during metestrus was 29.2% lower than during estrus. The hypoaminoacidemia at estrus may decrease availability of precursor for hepatic gluconeogenesis.