FEED UTILIZATION EFFICIENCY AND NITROGEN BALANCE IN DUAL PURPOSE COWS FED LOCAL DIETS IN THE SUBHUMID TROPIC OF MEXICO

Resumen

The objective of the study was to evaluate the effect of different levels of maize silage on feed utilization efficiency and nitrogen (N) balance in dual-purpose cows during the dry season. Nine crossbred cows with live weight of 423±12 kg were used. The treatments were: T1= 2 kg DM of maize silage + 3.9 kg DM of sorghum stubble; T2= 4 kg DM of maize silage + 1.8 kg DM of sorghum stubble; T3= 6 kg DM of maize silage. Additionally, all cows consumed Panicum maximum cv. Mombasa grass, supplemented with poultry manure and commercial concentrate in doses of 2.0, 2.9 and 2.3 kg DM, respectively. Data comparison was performed by ANOVA, and the experiment was conducted using a completely randomised mathematical model with three replicates. No significant differences (p >0.05) were observed for any of the variables evaluated. N intake reached 279.8 g day^–1 of which 8.5% was excreted in milk, 42.1% in faeces and 41.2% in urine. Milk production was 4.4 kg cow^–1 day^–1, with 33.1 g kg^–1 fat and 34.4 g kg^–1 crude protein (CP). N balance was 27.5 g cow^–1 day^–1, while utilization efficiency reached 8.6%. A higher inclusion of maize silage increased CP and N contents of the diet supplied to the cows, but it did not result in higher milk production. Feed utilization efficiency was limited even in the treatment with the lowest N content in the ration (T1). Further research is required to evaluate the economic and productive viability of the dietary inclusion of different silages, as a feeding strategy to cope with the low availability of forages during dry periods in low-scale milk production systems.