Milk Yield and Blood Serum Estrogens and Progesterone in Dairy Heifers

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Abstract
Relationships were measured of progesterone and total estrogens, or estrone and estradiol 17-.beta., in dairy heifers with their yield of milk in 1st lactation. Experiment 1 included 57 Holstein heifers where blood was sampled and body measurements taken at an average age of 123 days, ranging 91-172. Experiment 2 represented data on 62 heifers in 5 breeds, including 39 Holsteins, sampled and measured during the age intervals 130-170 (150), 180-220 (200) and 280-320 (300) days. Multilinear regression equations for milk in 1st lactation (305 days) on hormones, pedigree (dam''s milk in 1st lactation, sire''s Predicted Difference milk) and body dimensions (height, girth and length) were formed. In experiment 1, adjusted total estrogens, progesterone and their ratio accounted for 0, 25 and 10% of the variation in milk. Body dimensions and pedigree records together accounted for 20% of variation in milk. In experiment 2, adjusted nonzero estrone, estradiol and their ratio accounted for 4, 12 and 0% of the variation in milk at age 150 days; 11, 9 and 4% at 200 days; 1, 16 and 9% at 300 days. The combination of all 3 adjusted hormones accounted for 27% of the variation in milk experiment 1. Another set of 3 adjusted hormones in experiment 2 accounted for 27, 25, 20 and 51% of the variation for samples at the days of age 150, 200, 300 and jointly 150 with 200. Three hormone combinations accounted for more variation in milk than the body measurements and pedigree records as a set, except for age 300 days.