Effects of dietary fat and sire breed on puberty, weight, and reproductivetraits of F-1 beef heifers

Prepubertal Fl heifers (n = 246; from crossbred dams bred to either Herefor d [H], Limousin [L], or Piedmontese [P] sires) were fed 1.9% (LF) or 4.4% ( HF) dietary fat from 254 +/- 4 d of age until they reached puberty or the b reeding season started. Safflower seeds (37% oil with 79% linoleic acid) we re the added fat source. Blood samples and backfat thickness measurements w ere obtained from 60 randomly selected heifers representing the sire breeds and diets studied. In addition, five H-sired heifers from both diets were serially bled at 28-d intervals. Total gain, ADG, body condition score, and backfat thickness were affected by sire breed (P < 0.001) but not diet. Ba ckfat thickness was affected (P < 0.01) by the diet x time on feed interact ion. Diet did not affect pubertal age (P > 0.10) but tended (P = 0.08) to a ffect the percentage of heifers pubertal by the beginning of breeding (June 4). Sire breed effects on puberty age at beginning of breeding, percentage pubertal at the beginning of breeding, and puberty age during the entire s tudy were all highly significant. The effect of the diet x sire breed inter action on percentage of heifers pubertal at beginning of breeding (P < 0.05 ) was 74.4 vs 76.3% in H-sired, 69.8 vs 60.5% in L-sired, and 76.2 vs 97.6% in P-sired heifers (LF vs HF, respectively). Number of Al services per pre gnancy and final pregnancy percentage were not affected by diet or the diet x sire breed interaction. Diet affected progesterone (P < 0.05) and choles terol (P < 0.001) concentrations, and sire breed tended to affect (P = 0.06 ) cholesterol concentrations. The effect of the diet x time on feed interac tion on cholesterol concentrations was highly significant. There were no ef fects of diet or sample period on insulin or growth hormone concentrations in serially collected blood samples. We conclude that effects of supplement al dietary fat may be breed-dependent and hypothesize that a feeding period of approximately 60 d duration may be more appropriate than the 162 d used in this study.