EFFECTS OF DIETARY-FAT AND SEASON ON STEROID HORMONAL PROFILES BEFOREPARTURITION AND ON HORMONAL, CHOLESTEROL, TRIGLYCERIDES, FOLLICULAR PATTERNS, AND POSTPARTUM REPRODUCTION IN BRAHMAN COWS

Spring-calving Brahman cows (S) artificially inseminated to Brahman, A ngus, or Tuli sires and fall-calving Brahman cows (F) naturally bred t o Brahman were allotted randomly to receive 3.74% (LF; n = 9 S and 6 F ), 5.20% (MF; n = 8 S and 6 Fl, or 6.55% dietary fat (HF; n = 8 S). Di ets were formulated to contain differing fatty acid concentrations and to be isocaloric and isonitrogenous. Cows were bled and fed twice dai ly from 2 wk before expected calving date through d 21 after calving. Ultrasonography was performed on d 14 and 21 after calving. From d 21 to 90 after calving a sterile bull equipped with a chin-ball marker wa s placed with the cows to aid in estrus detection. In both seasons pro gesterone decreased (P < .01) and estradiol-17 beta increased (P < .01 ) as parturition approached. Cows receiving MF and HF had increased (P < .01) total numbers of follicles compared to LF cows, and cows recei ving MF had larger (P < .01) follicles. During the spring, cows receiv ing HF and cows bred to Brahman or Tuli sires had longer (P < .01) ges tation lengths. Progesterone concentrations before calving were affect ed (P < .01) by treatment x sire and estradiol-17 beta by a time x tre atment interaction (P < .01). Cholesterol after calving was higher (P <.01) in HF cows than in LF or MF cows. In the fall, LF cows had heavi er (P <.01) calves than cows receiving MF. Birth weight was also affec ted (P <.01) by treatment x sex of calf. Progesterone was affected (P <.01) by treatment x sex of calf. Estradiol-17 beta was affected (P < .01) by sex of calf and treatment x sex of calf. Across seasons, by d 90 after calving, 9 of 15 (60%) LF and 11 of 15 (73.3%) MF cows showed estrual behavior. Cows in the spring had increased (P < .01) numbers and larger follicles compared to the fall. In conclusion, dietary fat may influence steroid hormone concentrations before calving, calf birt h weight and postpartum follicular populations; furthermore, follicula r populations may also be influenced by season.