|Bellows, Susan - Bartlett|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2000
Publication Date: 9/1/2000
Citation: LAMMOGLIA, M.A., BELLOWS, R.A., GRINGS, E.E., BERGMAN, J.W., BELLOWS, S.E., SHORT, R., HALLFORD, D.M., RANDEL, R.D. EFFECTS OF DIETARY FAT AND SIRE BREED ON PUBERTY, WEIGHT, AND REPRODUCTIVE TRAITS OF F1 BEEF HEIFERS. JOURNAL OF ANIMAL SCIENCE. 2000. v. 78. p. 2244-2252. Interpretive Summary: Feeding 4.4% dietary fat increased the percentage of heifers puberal by the beginning of the breeding season. But the diet effect interacted with heifer breed and we hypothesize that response to supplemental fat may be breed dependent. Heifers with a low-fat body composition may have a different dietary fat requirement than heifers with a greater body fat composition. The feeding period in the present study was a maximum of 162 d in duration. Based on the results of other studies with supplemental fat and backfat changes in the present study we hypothesize that a feeding period of approximately 60 d before the beginning of the breeding season may be more effective in improving reproduction in replacement heifers.
Technical Abstract: Prepuberal F1 heifers (n=246) sired by Hereford (H), Limousin (L), or Piedmontese (P) bulls were fed 1.9% (LF) or 4.4% (HF) dietary fat from 254 d of age until heifers reached puberty. Safflower seeds (37% oil; 79% linoleic acid) were the added fat source. A 60-heifer sample representing sires and diets were bled and back fat thickness measured. Ten F1 H heifers representing diets were serial bled. Total gain, average daily gain, body condition score, and back fat thickness were affected by sire breed (P<.0001), but not diet. Back fat thickness was affected (P<.01) by the diet x time on feed interaction. Diet did not affect puberal age (P>.10) but tended (P=.08) to affect the percent of heifers puberal by begin breeding. Sire breed effects on puberty age and percent puberal at begin breeding and puberty age during the entire study were all highly significant. The diet x sire breed interaction effect on percent of heifers puberal at begin breeding (P<.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 (LF vs HF, respectively). Number of AI services per pregnancy and final pregnancy percentage were not affected by diet, or the diet x sire breed interaction. Diet affected progesterone (P<.05) and cholesterol (P<.001) concentrations. The diet x time on feed interaction effect (P<.01) on cholesterol concentrations was highly significant. Insulin or growth hormone concentrations were not affected by diet. We conclude effects of supplemental fat may be breed dependent and hypothesize that feeding for approximately 60 d duration may be more appropriate than the 162 d used in this study.