| Popis: |
We measured relationships of progesterone and total estrogens, or estrone and estradiol 17-β, in dairy heifers with their yield of milk in first lactation. Experiment 1 included 57 Holstein heifers where blood was sampled and body measurements were taken at an average age of 123 days, ranging 91 to 172. Experiment 2 represented data on 62 heifers in five breeds, including 39 Holsteins, sampled and measured during the age intervals 130 to 170 (150), 180 to 220 (200), and 280 to 320 (300) days. Multilinear regression equations for milk in first lactation (305days) on hormones, pedigree (dam's milk in first 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 three adjusted hormones accounted for 27% of the variation in milk in Experiment 1. Another set of three 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. |
