Association between protein feeding and reproductive efficiency in the dairy cow: specific emphasis on protein feeding in Finland

Associations between protein feeding and reproductive efficiency in the dai ry cow are reviewed. Examination of published data indicated that reproduct ive responses assessed as days open, services per conception or conception rate following changes in protein feeding tend to be inconsistent. Discrepa ncies can arise due to between-study variations in experimental design, sta tistical analysis, sample population size, uterine health, cow age, parity, reproductive management or nutrient intake. Detrimental effects on reprodu ctive efficiency following periods of excessive protein feeding are often a ttributed to increases in tissue urea and ammonia concentrations leading to impaired reproductive physiology, modified endocrine function or exacerbat ed postpartum negative energy balance. Examination of data collected from F innish dairy herds (n = 16 051) participating in the national milk recordin g scheme during 1993 indicated that milk production was maximised in herds fed diets containing 180 g crude protein/kg dry matter. In contrast, no con sistent relationships were identified between increases in on-farm protein feeding necessary to secure higher milk production and herd reproductive ef ficiency assessed as calving interval, first service interval and number of inseminations per calving. Further examination of data derived from 5 437 herds within the National recording scheme indicated that on-farm reproduct ive efficiency was independent of large variations in the mean annual urea concentration of bulk tank milk. It is concluded that increases in the crud e protein content of Finnish dairy cow rations from 150 to between 170 and 180 g/kg dry matter would allow improvements in milk production to be reali sed without leading to significant reductions in reproductive efficiency.