Milk yield and blood urea nitrogen in crossbred cows grazing Leucaena leucocephala in a silvopastoral system in the Mexican tropics

Abstract

The aim of the study was to assess milk yields, estimate the intake of crude protein (CP) and determine the concentrations of blood urea nitrogen (BUN) in early post-partum crossbred cows grazing irrigated Leucaena leucocephala (leucaena) in a silvopastoral system relative to those in an irrigated grass monoculture. Twenty-four multiparous cows were randomly allotted at calving on the basis of previous milk yields to 2 grazing treatments: grass monoculture system (MS) of Cynodon nlemfuensis (n=12); and an intensive silvopastoral system (ISS) composed of leucaena and C. nlemfuensis (n=12). Cows were supplemented with sorghum grain (ISS) or a conventional concentrate (MS) during milking to ensure availability of metabolizable energy (ME) and CP required for milk production. Mean estimated intake of leucaena was 5.1±1.3 kg DM/d and estimated CP intakes were 1,479±3.3 and 1,258±3.3 g/d for ISS and MS, respectively (P > 0.05), while estimated intakes of ME were 161±1.3 and 131±1.4 MJ/d for ISS and MS, respectively (P < 0.05). Milk yields were 13.5 and 14.5 kg/cow/d for cows on ISS and MS, respectively (P > 0.05). Concentrations of BUN were 19.1 mg/dL for cows in ISS and 15.3 mg/dL for cows in MS (P < 0.05). We conclude that intake of leucaena and sorghum grain in an irrigated silvopastoral system was sufficient to substitute for expensive concentrate in the diets of lactating cows grazing irrigated grass monoculture. However, the higher levels of BUN found in ISS suggest a lower efficiency of N utilization in this treatment. Restricting consumption of leucaena might be a means of improving efficiency of its use and this warrants investigation.