Body condition status at mating affects gestation length, offspring yield and return rate in ewes

Abstract

The present study was planned to determine the effect of ewe body condition score (BCS) and parities on fertility, return rate, gestation length, fecundity, litter size and lamb birth weight. Data were collected from 284 heads of ewes with first to fifth parity and raised at a state farm for three consecutive (2002-2004) years. Teaser rams were used to monitor estrus twice daily in the morning and in the evening from September to October. BCSs and body weights (BWs) were recorded at mating and postpartum. The ewes, at mating time in breeding season and within first 6 h after the expulsion of fetal membranes, were divided into four groups on the basis of their BCS: thin (BCS = <= 2.0; n = 70; 38), medium (BCS = 2.5-3.0; n = 122; 142), fat (BCS = 3.5-4.0; n = 72; 59) and very fat (BCS = >= 4.5; n = 20; 17). BCSs and BWs of ewes at postpartum were highly correlated with lamb birth weight (R = 0.486, P < 0.01, and R = 0.130, P < 0.05, respectively). BCSs and BWs of ewes at postpartum had positive effects on lamb birth weight (Y = 3.43 +/- 0.10 + 0.130 + 0.047 ewe body condition score (EBCS), P < 0.01; Y = 2.92 +/- 0.42 + 0.018 + 0.009 ewe body weight (EBW), P < 0.05 kg of lamb birth weight per BCS and kilogram of ewe live weight, respectively). The fertility rate, litter size and fecundity were higher in the medium and fat groups than thin and very fat groups (chi(2) = 10.607, P < 0.01). The BW and BCS at postpartum affected gestation length positively (P < 0.05). Return rate or number of coitus for conception were higher (P < 0.05) in thin and very fat groups than medium and fat groups. The data revealed that the ewes with medium and fat body condition (BCS = 2.5-4.0) scores were profitable.