Relationships between blood composition and fertility in dairy cows--a field study.

Three hundred and fifty-one lactating dairy cows, which were between 40 and 100 d post-calving, were selected from cows sampled during metabolic profile testing of 21 herds. Blood samples were analysed for packed cell volume (PCV), blood glucose and haemoglobin, and serum urea-N, albumin, total protein, inorganic phosphate, Ca, Mg, Na, K, Cu and Fe. After adjusting for herd and date of sampling and each cow's age, stage of lactation, milk yield and interval from calving to first service, concentrations of albumin and K (P less than 0-01) and PCV (P less than 0-05) were inversely related and concentrantions of globulins (derived as the difference between total protein and albumin) directly related (P less than 0-05) to the number of services required for conception. Conception rates to first service were inversely related to lactation number but not to milk yield on day of sampling.