Graduate Thesis Or Dissertation
 

Effectiveness of selection for productive characteristics in developing the Montana no. I hogs

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  • One of the most important productive characteristics of hogs is reproductive efficiency. Reproductive efficiency is best measured by litter size at weaning. Litter size at birth and weight of the pigs at birth are among the most important factors affecting litter size at weaning. It has been demonstrated that less than 5 per cent of pigs weighing 1.5 pounds or less at birth survive to be weaned. It was the purpose of this study to determine the selection for litter size and birth weight of the pigs and the effects of this selection on subsequent generations during the development of the Montana No. 1 line of hogs. The data for this study were made available through the agencies cooperating in the development of the Montana No. 1 hogs, the Montana Agricultural Experiment Station and the Bureau of Animal Industry, United States Department of Agriculture. To facilitate comparisons between generations all litters farrowed by sows which were her second or third litter were eliminated from the study. A significant difference between the average birth weight of pigs of gilts whose dams were gilts and the average birth weight of pigs of gilts whose dams were sows was determined by analysis of variance. The pigs farrowed by gilts by sows were heavier. All spring litters farrowed by gilts by gilts were used in the study from farrowing records taken from 1939 to 1949. The selection for litter size, based on the average litter size of the litters from which the individual pigs were selected, was for larger litters. There was an increase in the average litter size of litters farrowed by gilts by gilts. However, environmental influences accentuated the changes in litter size greatly during the period of development studied. The amount of selection, based on the birth weight of the individual pigs selected, weighted for the number of times their genetic influence was weighted on the succeeding generation was not positively associated with the birth weight of their offspring. The selection for birth weight based on the average birth weight of the litter from which individual pigs are selected is the best indication of their inherent ability to utilize available environmental conditions as well as their ability to provide an adequate uterine environment for their offspring. There was selection for pigs from litters with average birth weights below that of average of the population from which they were selected. There was a decrease in the average birth weight of the live pigs farrowed. It has been demonstrated that environmental influences are the major cause of variations in the birth weights of new born pigs within the litter. It is therefore possible that the ability of a sow to farrow pigs of greater uniformity at birth is a heritable characteristic. Using the within litter standard deviation of birth weights of live pigs farrowed for each litter as an index to the uniformity of the birth weights of the litters from which the parents were selected and the uniformity of the birth weights of their litters. It was concluded that the characteristic is heritable. There was selection and progress made in the development of the line toward more uniform litters at birth.
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