The concentrations of maternal immunoglobulin in 2-day-old lambs varied widely. They were significantly correlated with the lengths of pregnancy and the serum protein concentrations of the adult female sheep (ewes), but not with the colostrum immunoglobulin concentrations, nor with the weights or ratios of weights of the lambs and ewes. The mean concentrations were as high in Merino as in Blackface lambs.

Although there was some evidence that colostrum production was higher in ewes with twins than in ewes with single lambs, the immunoglobulin concentrations in the lambs fell significantly as litter size increased. They were significantly higher in male than in female twins, and in twins from litters containing both sexes than in twins from litters of one sex, but the difference between single males and females was not significant. Nor was the difference between the first and second born of each pair of twins. Twins and triplets born to ewes aged 7 years or more had particularly low concentrations. No other effects of the age of the ewe were found. The concentrations fell significantly as the date of lambing during the season advanced, and there were significant annual variations which could not be attributed to the weather. The correlation coefficients for the concentrations in lambs born to the same ewe in successive years were 0·309 and 0·298 (P < 0·001), respectively, for Merino and Blackface lambs.

The mean concentration in lambs which died subsequently from infections was significantly lower than in the surviving lambs, but many lambs with very low concentrations survived.