The maternal effects on growth and conformation in shire horse-shetland pony crosses

Abstract

Three foals produced by crossing a Shire stallion with Shetland mares were not significantly different in weight from pure Shetland foals. Two foals produced in the reciprocal cross were smaller than Shires, but the differences were not significant. The weights of all foals were about 8% of the weights of their dams. A comparison of the growth of 3 [female][female] of the different types of breeding showed that the cross-bred filly from the Shire dam grew especially rapidly until weaning at about 4 mos., after which there was a distinct drop in growth rate. The cross-bred did not grow nearly as rapidly as the purebred Shire, and the weight attained at 3 yr. was intermediate between average Shetland and Shire weights but greater than the weight of the cross-bred from the Shetland dam. The cross-bred from the Shetland dam grew only a little more rapidly than a pure Shetland filly, but after weaning the cross-bred filly from the Shetland dam grew much more rapidly than pure Shetlands. The difference between the 2 types of cross-breds was still very marked at 3 yr. of age. The differences in ratios between the measurements of body parts in cross-breds were not great. The maternal effects are suggested as due to (1) the maternal regulation of fetal nutrition, (2) maternal hormonal control, or (3) cytoplasmic inheritance. The interplay of genetic and nutritional factors in growth and development is considered.