Comportamiento de vacas lecheras primíparas y sus cruzas en un sistema a pastoreo de entre ríos (argentina)

Abstract

The purpose of this work was to evaluate different dairy genotypes during their first lactation in a grazing system with supplementation in Entre Rios, Argentina. We analyzed retrospective data from lactations of primiparous cows from five dairy genotypes: Holstein (H), H x Jersey (F1), F1 x Brown Swiss (P), F1 x Guernsey (G) and triple backcross of cows crossed with H. The cows showed different birth weights in 2007 and 2010, while age at first birth showed differences in F1 in 3 of the 4 years. The genotype G appears to have the lowest and most constant calving to conception interval (ipc) in each year, F1 was the best in the last three periods and H always showed a low reproductive efficiency, confirming that the major productions were associated with poorer reproductive indicators. The number of services per pregnancy and lactation on the whole go with the general ipc trend, but has a great variability within each genotype, rotating the performance of the genotypes according to the year. Milk production was above 6,000 liters in all of them, being H the one that stood out when environmental and food conditions were favorable. Production of butiric fat and total protein were highly variable among genotypes and years, being H and G the most productive. It can be concluded that the variations within each genotype analyzed and the different proresponses that each of them produced do not explain adequately the possible adaptation of the animals to the current environment and management, although it could be argued that F1 and G genotypes are the most stable as regards production and offer the best reproductive responses for these conditions.