The impact of somatotropin, milking frequency, and photoperiod on dairy farm nutrient flows

Three technologies that increase milk production per cow and that are avail able to dairy producers are bovine somatotropin, three times daily milking, and extended daily photoperiod. Dairy herds fed according to National Rese arch Council requirements were simulated to predict the impact of these tec hnologies on N losses to manure and to water resources. Because Dairy Herd Improvement Association total lactation records (n = 93,080) revealed a pos itive linear relationship between 305-d milk production and calving interva l, calving intervals were predicted to increase with the use of technologie s and to result in a change in the ratio of lactating cows to growing heife rs in a herd. Compared with a herd using no technologies, the use of bovine somatotropin, three times daily milking, or extended photoperiod were pred icted to reduce herd N excretion per unit of milk by 7.8, 7.0, and 3.6%, re spectively. When the use of all three technologies was simulated, N losses to manure were decreased by 15.7% when assuming calving interval increases from the technologies or 15.4% without accounting for calving interval incr eases. Reductions in feed N requirements and manure N losses with these thr ee technologies were predicted to reduce environmental N loading by up to 1 6%.