Analysis of reproductive indexes in Friesian ewes according to female category and year of study

Abstract

The literature indicates that dairy genotype sheep have high fertility, prolificacy, maternal ability
and precocity. However, there are few reports on reproductive performance under the most
widespread breeding conditions in Argentina. The objective was to analyze reproductive
performance in Friesian sheep according to the category of female (young and adult) and the
year of study (2013, 2014 and 2015). The data were obtained during three consecutive years
from a flock composed of Friesian ewes (pure and crossed), exploited in Uribelarrea, Buenos
Aires, Argentina, on pastoral basis with strategic supplementation. The females, categorized as
"young" (“milk-teeth” and “2-tooth”) and "adults" (“4-tooth” or more), were served in autumn for
60 days. The reproductive indexes were analyzed using Genmod (SAS), according to category,
year and their interaction. The young females had lower %Pregnancies (73.33 vs. 92.96%, P
<0.01) and %Multiple births (22.73 vs. 52.39%, P <0.05), finally weaning fewer lambs than the
adults (0.83 ± 0.13 vs. 1.32 ± 0.08, P <0.05), attributable to the lower performance of “milk-teeth”
females. The %Parities and %Mortality of lambs (%Neonatal mortality and %Weaning mortality)
did not depend on the category (P <0.05). The year did not affect any of the reproductive
indexes (P <0.05).