Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

Robert C. Lamb


Robert C. Lamb


David L. Turner


Jay W. Call


A study was conducted to analyze reproductive data gathered over a ten-year period at the Utah State University Dairy Farm. The study utilized 289 complete first lactations of Holstein cows, including 150 daughters of 10 sires in Trial I and 139 daughters of 8 sires in Trial II. One sire was used in both trials; this was sire 4 in Trial I and sire 18 in Trial II. The study measured ration, season, and sire effects and their interactions on the reproductive performances of dairy cows.

Reproductive traits analyzed were: days from calving to first estrus, days from calving to first breeding, days from first breeding to pregnancy, days open, number of services per pregnancy, pregnancy rate, calving interval, number of estrous cycles to first breeding, and number of estrous cycles to pregnancy.

Sire effect examined the effect of predicted difference for milk (PDM) of sires on reproductive performances of their daughters. There was 1352- kg PDM difference between lowest and highest sire. There was no sire effect among North American sires, but daughters of one sire from New Zealand had significantly lower reproductive performance. Reproductive performance of daughters was not related to PDM of sire.

Ration affected calving interval in the comparison of all four rations. But more data is needed to verify this because only one sire had daughters on all rations.

Effect of season of calving on days open and days from first breeding to pregnancy is also very questionable because of small numbers of daughters in some seasons. Ration by season interaction affected days open, services per pregnancy and pregnancy rate. The high energy ration enhanced reproduction in cold season and low energy was more beneficial in cows calving in hot season.

There was no sire by ration interaction effect.



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