The effect of ewe body condition at lambing on colostral immunoglobulin G concentration and lamb performance.

Body condition was scored at lambing (BCSL) on 101 mature (4 to 7 yr old) Polypay ewes and related to colostral immunoglobulin G (IgG) concentration and lamb performance. Colostrum samples were collected from each ewe within 12 h of lambing and litters of more than two lambs were reduced to two within 2 h of lambing. Colostral IgG concentrations decreased rapidly with time (b = -3.28; R2 = .2132) and linear regression analysis projected that colostral IgG concentrations would diminish to zero milligrams/milliliter by 23 h postpartum. Body condition score at lambing varied from 2.5 to 3.5 and had no effect on colostral IgG concentration, which averaged 79 +/- 5.6 mg/mL, adjusted to the time of parturition. Total birth weights of lambs were higher for the oldest ewes (7 yr old), but this group had the lowest prolificacy. This age group weaned the lowest total lamb weight and number of lambs. Total weight of lambs born was not affected by BCSL. Lamb mortality from birth to weaning was 19.0% and was not affected by BCSL, sex, litter size, or breed of sire, but the older (7 yr old) ewes had greater lamb mortality. Total weight of lamb weaned was not affected by BCSL, although ewes with a BCSL of 3.0 tended ( P = .11) to wean more kilograms of lamb than ewes with a BCSL of 3.5. Ewes bred to Polypay rams weaned more total weight of lamb than those bred to Columbia rams, which was due to increased survival rate to weaning for the Polypay rams. We conclude that, within a range of 2.5 to 3.5, BCSL is not an important factor affecting the colostral IgG concentration, total weight of lamb born, lamb mortality, or total weight of lamb weaned.