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Thesis (M.S.)—University of Nebraska—Lincoln, 1963. Department of Animal Science.


Copyright 1963, the author. Used by permission.


The present investigation was designed and conducted to determine the effect of heterosis on age of puberty, ovulation rate, embryo survival, and litter size at 30 days of gestation. These traits were measured in straightbred and crossbred gilts mated at the same sexual age (second estrus) and maintained on either a high or restricted plane of nutrition during the estrous cycle prior to breeding. This made it possible to determine whether or not the expression of heterosis is influenced by plane of nutrition. A study was also made of the effect of the sire on the reproductive phenomena examined.

Seventy-five purebred (forty-three Duroc and thirty-two Yorkshire) and seventy-nine reciprocal-cross gilts (twenty-three Duroc-York). And ffty-six York.-Duroc) gilts representing five Duroc and five Yorkshire sire-families were used to study the effects of heterosis and plane of nutrition just prior to breeding (flushing) on age and weight at puberty, ovulation rate at second estrus, and embryo survival and litter size at 30 days of gestation. The effects of sire-family, breed of sire, breed of dam, and the interactions of these sources of variation and heterosis with plane of nutrition were also studied. All of the gilts were fed a low energy, high fiber (18%) ration prior to puberty and following breeding at second estrus. One-half of the gilts in each breeding group was switched to a high energy, low fiber ration during their first estrous cycle. One-half of the gilts in each breeding group was mated to Duroc boars and the other half to Yorkshire boars; pure-bred dams carried either purebred or crossbred embryos.

Advisor: Dwane R. Zimmerman