For the return to estrus rate and adjusted farrowing rate the comparison of means was
performed with the aid of χ2-test. For litter size and the number of piglets produced in a
100 bred sows an analysis of variance was performed by the GLM procedure (SAS, 1998).
The model used was Y = μ + cyst + e, where Y is the dependent variable (i.e., litter size
or number of piglets produced in 100 bred sows), μ the overall means, cyst the presence
or absence of cysts and e the error. The effect of farm, parity, visual condition score, back
fat, lactation length, weaning to estrus interval, season, and interaction between farm with
lactation length, farm with weaning to estrus interval were also tested, butwas later removed
from the model for not having been significant (P > 0.05). Adjusted means were compared
by Student’s t-test.