THE INFLUENCE OF LACTATION LENGTH ON THE OCCURRENCE OF NON-INFECTIOUS REPRODUCTIVE FAILURE IN A LARGE COMMERCIAL HERD
K. Van Gelder and G. Bilkei

Abstract
The trial was conducted on an East European breeding company farm with 5600 sows. Based on length of lactation, a large number of healthy, parity 2-5 sows were randomly assigned to 9 different weaning age groups (weaning at 5- 7; 8-10; 11-13; 14-16; 17-19; 20-22; 23-25; 26-28 or 29-35 days).
???? The parameter: A: "regular returns to oestrus," B: "irregular returns to oestrus," C: "anoestrus," and D: "other reproduction related reasons of reproduction failure (RF)/culling," were evaluated.
???? Compared with those lactating 17-19 days, sows lactating 5- 7, 8-10 or 11-13 days had a higher (P<0.01) proportion of "regular returns to oestrus," "irregular returns to oestrus" and "anoestrus." These parameters had a tendency to decrease as lactation length increased. Sows with lactation lengths of 20-22 and 26-28 days showed significantly less (P<0.05) anoestrus when compared to the sows lactating 17-19 days. Sows lactating 14-16 days had a significantly higher (P<0.01) proportion of animals returning to oestrus due to "other reproduction related reasons of RF/culling."
???? Anoestrus was found in 20.62 % of RF cases. No oestrus was shown in 17.14 % of sows in the <16 days weaning groups but only 3.48 % of sows weaned >20 days had anoestrus. Sows weaned >20 days showed markedly higher "other reproduction related reasons of RF/culling" than sows weaned at <16 days of lactation.
???? The results indicate that in healthy sows in this unit, a lactation length of 17-19 days compared with shorter lactation lengths, results in lower RF rates.

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