THE EFFECT OF DIETARY AND CLIMATIC FACTORS ON FERTILITY, AND ON PLASMA PROGESTERONE AND OESTRADIOL-17β LEVELS IN DAIRY COWS

Abstract

The effects of high dietary protein concentrations, high ambient temperatures and low dietary β-carotene levels on fertility and on plasma progesterone and oestradiol-17β levels in high-yielding dairy cows, are described. High-yielding dairy cows were fed diets containing 15 or 20% crude protein. Cows fed the higher level of protein were less fertile and had a lower plasma progesterone concentration during the oestrous cycle preceding the first insemination. This phenomenon was especially pronounced in cows fed a diet containing 85% concentrates and 15% hay, where plasma progesterone levels during days 9–17 of the oestrous cycle were 2.5–3.7 ng/ml in cows fed the high level of protein and 4.0–5.5 ng/ml in cows fed the low level of protein (P ≤ 0.05). In cows fed 50% more energy before parturition, plasma progesterone levels did not differ between animals fed the low and high protein diets.