Abstract

MARINI, P.R.; CASTRO, R.  and  FRANA, E.. Eficiencia biológica de biotipos lecheros de primera lactancia en sistemas a pastoreo. Rev. vet. [online]. 2015, vol.26, n.2, pp.136-142. ISSN 1669-6840.

The aim of this study was to evaluate the biological efficiency of dairy cows of different biotypes in grazing systems. The data of 271 first lactation cows collected between 1992-2012 in Santa Fe (Argentina), were used. Retrospective data of dairy cows, divided into two categories: pure cows (n=106) and record breeding cows (n=165), were employed. Considered variables were: age at first calving (in days, EPP), interval between first lactation second conception (in days, IPC), milk production adjusted to 305 days of lactation (in liters, PL) and amount of butyrous fat produced (in kg, GB). Univariate techniques (Student "t" test) and multivariate system (principal components) were considered for statistical analysis. Significant differences between PL and GB were registered. Pure cows produced more milk (478 liters) and more fat (40 kg). No statistical differences were found between both groups regarding age at first lactation (which tended to be higher for not pure cows: +19.5 days) or calving conception interval (which tended to be higher for pure cows: 15.5 days). The first two principal components accounted for 75.25% of the total observed variance. The first component explained 44.60% of variance and correlated negatively and significantly with milk production (PL: r=-0.836) and fat production (GB: r=-0.939) and second component explained 30.65% of variance and correlated negatively and significantly with age at first calving (EPP: r=- 0.795) and positively with calving conception interval (IPC: r=-0.674). In conclusion, the studied biotypes behave differently between them, though they agree that cows took longer to have their first lactation, respond productive and reproductively higher so that the cows that calved before their first calf, regardless its original biotype

Keywords : dairy cow; first lactation; efficiency; grazing system.

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