| Abstract: | Objectives: The objectives of this study were to examine possible
relationships between pregnancy loss (described as the
loss of pregnancy occurred after a positively diagnosed pregnancy
-days 28-40- and before day 110 of pregnancy) and different
factors such as synchronization protocol used, parity,
number of Artificial Insemination (AI), days in milk at AI, age at
AI (in the case of heifers) and the fact of having had a previous
pregnancy, in dairy cows managed under intensive milk production
systems.
Material and methods: A total of 12978 AIs from seven different
farms were included in the study. The number of AIs from
each farm were 812/12978 from farm 1 (6.3%), 710/12978 from
farm 2 (5.5%), 1865/12978 from farm 3 (14.4%), 4104/12978
from farm 4 (31.6%), 1530/12978 from farm 5 (11.8%),
589/12978 from farm 6 (4.5%) and 3368/12978 from farm 7
(26.0%). A total of 5119 were first AIs and 7859 were second or
more AIs (from them 1729 were 5th or more AIs). The AIs were
performed in animals with different lactation orders, with 1586
AIs having been in heifers (only from farms 4 and 7), 3983 in
primiparous cows, and the rest in multiparous cows (with lactation
order up to 9th). Synchronization protocols recorded were
observed estrus, G6G, Double Ovsynch, Presynch, Ovsynch
(with or without intravaginal dispositive), 5dCosynch (with or
without intravaginal dispositive). A total of 10186 AIs was performed
during the cool season (September to May) and 2792
during the hot season (June, July and August). Straightforward
stepwise Wald logistic regression analysis was used to study
the influence of the different factors, including the factor farm
as covariable in the model.
Results: Average conception rate for all AIs was 36.7%, and
average pregnancy loss was 13.9% (664/4764). The range
among farms oscillated from 9.5% (28/294) to 16% (194/1209),
with the factor “farm” being a significant one affecting pregnancy
loss (P<0.0001). When all AIs were included into the model
(controlled including the factor “farm” in the model), significant
factors affecting pregnancy loss were season with the hot season
increasing the risk of pregnancy loss (11.6 vs. 14.5%; OR,
1.539; 95% CI, 1.215–1.949; P<0.0001); the number of AIs,
with second or more inseminations showing an increased risk
(14.2 vs. 10.5% for first and second or more AIs, respectively;
OR, 0.696, 95% CI, 0.581–0.834; P<0.0001), the parity using
the stage of heifer (nulliparous) as reference value, and both
primiparous and multiparous increasing the loss risk when
compared to the heifers (7.8 vs. 9.9 vs. 14.7% for heifers, primiparous
and multiparous, respectively; OR, 1.854, 95% CI,
1.330–2.585; P<0.0001 for primiparous cows, and OR, 3.057,
95% CI, 2.248–4.157; P<0.0001 for multiparous cows). The
fact of having had a pervious pregnancy loss was demonstrated
as a “protective factor (OR, 0.445, 95% CI 0.278–0.713;
P<0.0001). Synchronization protocol did not affect significantly
pregnancy loss. When heifers were separately studied (n=1586
AIs), in order to explore the effect of age at insemination a significant
effect of this factor was (OR, 1.026, 95% CI, 1.016–
1.035; P<0.0001), besides the significant effect of number of AI
observed with second or more inseminations showing less
rates of pregnancy loss (OR, 0.305, 95% CI, 0.120–0.774;
P=0.012). In the case of primiparous cows separately analyzed
(n=3982 AIs), besides farm (P<0.0001) and season (OR, 1.855,
95% CI, 1.252–2.747; P=0.002) no other factor was kept in the
model as significant factor; and in the case of multiparous cows
(n=7409AIs) season (OR, 1.647, 95% CI, 1.221–2.221;
P=0.001), second or more insemination (OR, 0.640, 95% CI
0.513–0.799; P<0.0001) and having had a pervious pregnancy
loss (OR, 0.340, 95% CI 0.189–0.610; P<0.0001) influenced
significantly pregnancy loss. Synchronization protocol and days
in milk at insemination did not significantly affect the risk of
having pregnancy loss in adult cows (P>0.05).
Conclusions: Our study suggests that the cool season, a higher
number of insemination, a younger age of the dam in the
case of heifers and having previously suffered pregnancy loss
are protective factors for pregnancy loss. However, these factors
seem to affect in a different way depending if the inseminations
are performed on heifers, primiparous or multiparous
cows, which highlights the different reproductive characteristics
of the dairy cattle. |
