Utilization of lipid by primiparous beef heifers during the postpartum period.
Shelby J. Filley, Harley A. Turner, and Fredrick Stormshak
Department of Animal Sciences, Oregon State University, Corvallis
Eastern Oregon Agricultural Research Center, Burns, OR, October 1997
Research in Progress
RESEARCH QUESTION
The interval between calving and resumption of estrous cycles is longer in beef heifers bred to calve for the first time as two-year olds than in multiparous beef cows. Longer anestrous periods decrease pregnancy rates, which represents a significant monetary loss. Therefore, it is beneficial to shorten anestrous periods of primiparous beef heifers. Fertility resumes after the uterus returns to its pre-pregnant state through a process of uterine involution and repair and the ovaries begin to ovulate. The goal of this study was to provide lipids to first calf heifers early in the postpartum period in order to shorten the postpartum interval by stimulating production of hormones required for uterine involution and ovarian activity.
LITERATURE SUMMARY Prostaglandin F2alpha (PGF2alpha ), a hormone important for uterine involution, is negatively correlated with the number of days to complete uterine involution and the length of interval between parturition and resumption of normal ovarian activity. Prostaglandins are derived from dietary linoleic acid, an essential fatty acid (lipid). Intravenous infusion of lipids has been shown to increase PGF2alpha and alter follicular dynamics in estrous cycling heifers and ewes.
STUDY DESCRIPTION Two experiments were conducted to investigate the ability of postpartum heifers to utilize lipid for production of PGF2alpha and to determine if heifers receiving fat would have a shorter postpartum anestrus than controls. Experiment I: 20 heifers were administered either lipid (soybean oil) or control (50% dextrose or saline) solutions during 4-hr intravenous infusions on day 7 through 11 postpartum (PP). PGF2alpha concentrations in plasma were monitored during the infusion periods. On day 12 PP, heifers were given 150 IU of oxytocin to evaluate the capacity for PGF2alpha production. Experiment II: In 1996 and 1997, a total of 100 primiparous heifers were fed diets supplemented with either lipid (Ca salts of palm oil) or barley (isocaloric control) for the first 30 days PP. PGF2alpha concentrations in plasma were monitored during the feeding period. For both experiments I and II, return to estrus was determined by twice daily heat checks using intact bulls and twice weekly blood progesterone analysis. Pregnancy rate was determined by rectal palpation.
APPLIED QUESTIONS
Does infusion of lipids increase PGF2alpha in postpartum heifers? Compared to controls, plasma of heifers infused with lipids contained greater amounts of the PGF2alpha precursor (linoleic acid). Also, the lipid infused heifers had increased plasma PGF2alpha concentrations during the infusion period. As indicated by their increased plasma PGF2alpha after oxytocin injection, the capacity of the lipid infused heifers to produce PGF2alpha was greater than that of controls.
Does short term infusion of lipids improve fertility in heifers? Number of days to first estrus and pregnancy rates were not different among treatments in this infusion experiment. There was no improvement in fertility with short term infusion of fatty acids to this small group of heifers.
Does supplementation of diets with fat increase PGF2alpha in heifers? This feeding experiment is still in progress. Early results from year one (1996) show plasma of heifers receiving the Ca salts of fatty acids contains greater amounts of the PGF2alpha precursor (linoleic acid) and also greater concentrations of plasma PGF2alpha as compared to heifers receiving the barley supplemented diet. Results for PGF2alpha from year two (1997) are still pending analysis.
Does lipid supplementation of diets improve fertility in heifers? Reproductive data are not yet summarized for this experiment.
