Influence of nutrition on serum concentrations of progesterone, luteinizing hormone and estrous behavior in dairy heifers

Thirty postpubertal Holstein heifers were used to investigate the influence of dietary intake on 1) serum concentrations of progesterone (P4) and luteinizing hormone (LH) during diestrus and 2) estrous behavior. Heifers were randomly allotted to receive either 80, 100 or 120% of the National Research Council (NRC) requirements for energy, protein and dry matter intake for 139 d. Heifers were fed their respective diets in groups in outdoor lots for 114 d at which time individual feeding of diets was initiated in a stanchion barn. Estrus was synchronized with two injections of prostaglandin (PG) so that on d 138 of dietary treatment the heifers were in diestrus (means = d 8 of estrous cycle). Also, on d 138, blood samples were collected via jugular cannula at 20-min intervals for 12 h beginning at 0630. After collection of the 37th blood sample, all heifers were treated with PG and additional blood samples were collected at 1-h intervals for 24 h. Immediately thereafter, all heifers were moved to a common outdoor lot for 72 h of continuous observation for estrous behavior. Weight gains during the experimental period differed among groups and were 46 +/- 5, 83 +/- 5 and 113 +/- 4 kg for the heifers fed 80, 100 and 120% of the NRC requirements, respectively. Mean serum concentrations of P4 for the 80% NRC group (4.6 +/- .6 ng/ml) tended to be lower than both the 100% (5.9 +/- .6 ng/ml) and 120% (6.0 +/- .5 ng/ml) NRC groups, respectively. Mean serum concentrations of LH, number of LH secretory peaks/12 h and LH peak amplitude were similar among all NRC groups. Rate of decline in serum P4 after PG was also similar among all NRC groups.(ABSTRACT TRUNCATED AT 250 WORDS)