Date of this Version
Thesis (M.S.)—University of Nebraska—Lincoln, 1964. Department of Dairy Science.
From an economic standpoint it would be desirable if dairy cows could calve once a year. The gestation period is from 273 to 292 days and it is generally not recommended to breed cows until 60 days post-partum. Since many cows require more than one breeding for conception the average calving interval is more than 12 months. A shortening of the gestation period would make it possible to approach the 12 months calving interval. On the other hand, most breeders want a fairly large calf for which reason it becomes important to know the relationship between gestation length and birth weight.
Both gestation length and birth weight show considerable variation. If the breeder wants to change the gestation length or the birth weight or both by selection, it is important to know how much of the variation in these two characteristics is caused by genetic factors and how much may be due to environmental factors of one kind or another. It is also important to know the relationship between birth weight and gestation length.
This study deals primarily with heritability and repeatability estimates of gestation length and birth weight of the calf. In addition the genetic and environmental relationships between these characteristics have been investigated.
Advisor: Mogens Plum