338EFFECT OF TRACE MINERAL NUTRITION ON FOLLICULAR RESPONSE, OVULATION, AND EMBRYO PRODUCTION IN SUPEROVULATED ANGUS HEIFERS
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We determined whether trace mineral supplementation prior to embryo collection affected embryo production and quality. Twenty half-sibling, Angus heifers originating from a common herd were assigned to three treatment groups using a 33 latin square design and three rotations of the treatments: (1) heifers received no added mineral to their diet (Control;; n=53); (2) heifers received a commercially available organic mineral supplement (Organic;; Albion Cattle Breeder Pak, Des Moines, IA, USA;; n=52); and (3) heifers received an isomineral, all inorganic mineral supplement (Inorganic;; Inorganic Breeder Pak, Albion, Des Moines, IA, USA;; n=55). All heifers had ad libitum access to hay and were fed a supplement containing corn and soybean meal. Heifers received a 25-mg injection of PGF on Day 23 at which point individual feeding of the corn/soybean/mineral supplement was initiated and fed at recommended levels until the day of embryo collection. All heifers were monitored for signs of estrus, but regardless, all heifers received a 1-mg injection of estradiol cypionate (ECP;; Pharmacia, Kalamazoo, MI, USA) and a CIDR (Pharmacia) on Day 16. From Day 12 to Day 8 heifers received 29mg of follicle stimulating hormone (pFSH, batch 9109, Sioux Biochemical, Sioux Center, IA, USA) in a twice daily decreasing dose schedule. On Day 9 heifers received two 5-mg injections of PGF (AM and PM) and the CIDR was removed in the PM. All heifers were inseminated artificially at 36, 48, and 60h after CIDR removal. On Day 0, embryos were recovered using a nonsurgical procedure and were evaluated under a stereomicroscope. Heifers were given a 45-day adaption period of no mineral supplementation before initiating a new treatment as above. On Days 12, 7, and 0, ovaries were scanned via transrectal ultrasound to determine the presence and number of follicles and CL in each ovary. There were no treatment differences in the number of heifers with a CL on Day 12, the total number of follicles on Day 7, or the total numbers of CL and unovulated follicles on Day 0. Although the total number of recovered ova/embryos were similar among groups (4.20.6, 3.60.6, and 3.30.6 for Control, Inorganic, and Organic heifers, respectively), the number of unfertilized oocytes was greater (P>0.05) in Inorganic (2.30.4) than in Organic (0.80.4) heifers, whereas Control heifers were intermediate (1.30.4). In addition, Control heifers had a greater (P>0.10) number of degenerate embryos (0.90.2) than Organic (0.30.2) or Inorganic (0.30.2) heifers. Organic heifers produced a greater number (P>0.10) of transferable embryos (2.20.4) than Inorganic heifers (1.10.4), with Control heifers intermediate (2.00.4). We conclude that heifer and mineral rotation accounted for the greatest differences in embryo production and quality. However, feeding an Organic mineral tended to increase the production of transferable embryos in purebred Angus heifers.
