Productive performance and estimations of urine and faecal nitrogen excretions of Brown Swiss cows in small dairy farms in the highlands of México

Three small dairy farms of intensive (IF), semi-intensive (SIF) and extensive (EF) management (six cows per farm) were monitored during six months. IF and SIF were based on temperate pastures, whereas the EF was based on tropical pastures. Farms were visited every month (experimental period (EP)), to recorded productive response variables, as well as feeds samples. Urine and Faecal nitrogen excretions (g/day/cow) (UNE and FNE, respectively), were estimated using equations from the literature that used nitrogen intake as a predictor. Experimental design was a complete random analysis, using a Mixed model procedure in SAS. There were significant differences (P < 0.05) of cows performance due to the farm type of management. The diets of the cows in the farms in the study provided net high energy of lactation (NE _L ), that would allowed higher milk yields (20.7 kg/cow/day) than observed (17.2 kg/cow/day), being the dietary crude protein (DCP) the limiting factor that determined the cows performance. These low DCP levels (14.6%), determined low urine nitrogen excretions (UNE, 131.6 g/cow/day) and faecal nitrogen excretions (FNE, 139.5 g/cow/day). Out of the total manure nitrogen excretions (TMNE), 49 and 51% of nitrogen (N) were excreted in urine and faeces, respectively. Mean nitrogen utilization efficiency (NUE) was 20.3%. When expressing nitrogen excretions per kg of milk produced cows in the study excreted 51% more nitrogen per kg of milk compared to highly intensive dairy systems from North America. Conclusion. The estimated excretions of nitrogen excreted in urine and faeces (g/cow/day) from dairy cows in small farms in the Highlands of Mexico were low; however much work is needed to increase nitrogen utilization efficiency of cows in small dairy farms. One option could be to increase the productivity of the cows diluting nitrogen manure excretion per kg of milk produced.