Age at puberty, total fat and conjugated linoleic acid content of carcass, and circulating metabolic hormones in beef heifers fed a diet high in linoleic acid beginning at four months of age1

Abstract

In the current study, we hypothesized that diets high in linoleic acid would increase conjugated linoleic acid (CLA) tissue content, reduce adiposity and leptin production, and result in an increase in the age at puberty in heifers. Heifers were weaned and blocked by body weight (heavy, n = 10, and light, n = 10) and allocated randomly within block to receive isocaloric and isonitrogenous diets with either added fat (HF, n = 10) or no added fat (C, n = 10) from 4 mo of age until post-pubertal slaughter. Whole sunflower seed (55% oil; 70% linoleic acid) was used as the fat source in HF diets and provided 5% added fat from the start of the study until heifers weighed 250 +/- 8 kg, at which time added fat was increased to 7% of dry matter until slaughter. Body weights were recorded weekly, and blood samples were collected weekly for total cholesterol and hormone analyses. Puberty was confirmed based on serum concentrations of progesterone and ultrasonographic confirmation of corpora lutea. Heifers were slaughtered at 325 +/- 10 d of age, and longissimus muscle between the 9th and 11th rib was collected and analyzed to estimate carcass composition. Subcutaneous and kidney, pelvic, and heart fat were collected at slaughter for fatty acid analyses. The HF heavy group tended (P < 0.10) to reach puberty later than all other groups, and one HF light heifer did not reach puberty during the study. Linoleic acid and cis-9, trans-11 CLA tissue contents were higher (P < 0.03) in HF heifers than controls, but neither total carcass fat nor percentage of dry matter differed by dietary group, although the percentage of protein tended (P < 0.10) to be lower in HF heifers. Mean serum concentrations of leptin did not differ due to diet; however, leptin increased (P < 0.01) linearly as puberty approached. Circulating concentrations of growth hormone and insulin-like growth factor I increased or remained relatively constant between wk 2 to 10 of feeding, and then declined (P < 0.01) until the onset of puberty. Serum IGF-I was lower (P < 0.01) in heifers receiving the HF diet. Mean serum concentrations of insulin and total cholesterol increased (P < 0.01) with time in both groups, but only total cholesterol was increased by the HF diet (P < 0.05). Results indicate that diets high in linoleic acid fed to growing beef heifers beginning early in life have little or no effect on total carcass fat, circulating leptin, or age at puberty despite measurable increases in CLA accumulation.

Heifer fertility and carry over consequences for life time production in dairy and beef cattle

“…The circulating concentration of IGF-1 is highly correlated to BW and growth rate during the period of pre-pubertal growth (Lammers et al, 1999;Brickell et al, 2009a). In contrast, Garcia et al (2003) found that IGF-1 levels in beef heifers declined in the 10 weeks preceding puberty. These differences may relate to differences in ages at which puberty is reached and/or nutritional management in different studies.…”

Utilization of soybeans or corn milling by-products in beef heifer development diets1,2

“…Among the heifers fed SB and responding to estrous synchronization in the preliminary experiment, the interval from PGF 2α to estrus (76.6 h) was prolonged compared with heifers fed diets containing WCGF (69.2 h). Studies are limited on the use of fat supplements in replacement heifer diets; however, these studies agree with others demonstrating no beneficial or detrimental effect of supplementing fat from a variety of sources at inclusion rates of 2 to 5% of DM (Funston et al, 2002;Garcia et al, 2003;Howlett et al, 2003).…”

Effects of supplementation of whole corn germ on reproductive performance, calf performance, and leptin concentration in primiparous and mature beef cows1

“…Supplementing Holstein heifers with rumen bypass fatty acids or CLA from 3 to 5 mo of age until the third postpubertal estrus had no effect on plasma leptin (Block et al, 2003). Similarly, feeding sunflower oil to heifers beginning at 4 mo of age did not change leptin concentration (Garcia et al, 2003). Leptin also was unchanged by addition of 6% sunflower oil to the finishing diet of Wagyu or Limousin steers (Johnson et al, 2001b).…”