Doctoral Dissertations

Date of Award

12-1997

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

James K. Miller

Committee Members

James Bailey, Fred Hopkins, James Quigley, John Waller

Abstract

Study 1. The hypothesis that incidence of retained fetal membranes can be reduced by limiting oxidative stress was evaluated with 56 Holstein and 8 Jersey primigravid heifers and 64 Holstein and 16 Jersey multiparous cows. Cows and heifers were supplemented with an antioxidant (vitamin E), a site specific damage retardant (Zn) or a potential prooxidant (Fe) in a 2 X 2 X 2 factorial arrangement during the last 42 d prepartum. Amounts of supplements per animal daily were 1,000 IU of vitamin E (as d,1 α-tocopheryl acetate), 0.8 g of Zn (supplied half by Zn-methionine and half by ZnSO4) and 12 g of Fe for Holsteins and 9 g of Fe for Jerseys (as FeSO4-7H2O). Incidence of retained fetal membranes was unaffected by supplementation of vitamin E or Zn. Although not directly affected by treatment, cows that retained fetal membranes had lower plasma α-tocopherol (P = 0.03). Similarly, cows that were not supplemented with vitamin E had lower plasma α-tocopherol (P < 0.001). Iron did not have any direct negative effects on reproductive performance. Cows receiving additional Fe, however, had lower unsaturated iron binding capacity (P = 0.004) which in turn was also lower (P = 0.03) in cows that retained fetal membranes. Supplementation with vitamin E or Zn reduced days to first estrus (P<0.005). Vitamin E reduced days to first service (P = 0.04) and Zn tended to reduce days to first service (P = 0.08). Vitamin E tended to reduce days open (P = 0.06). Days open were not affected by supplementation of Zn. Services per conception or milk production were not affected by supplementation. Vitamin E and Zn were not directly effective at reducing the incidence of retained fetal membranes. However, vitamin E may be associated indirectly with retained fetal membranes through plasma a-tocopherol. Vitamin E and Zn were beneficial in the reduction of days to first estrus, indicating improved reproductive health in the early post partum period.

Study 2. The objectives of this research were: 1) to determine if organically complexed zinc, manganese, copper and cobalt would improve reproductive performance and (or) milk and milk component production in lactating dairy cows that started receiving bovine somatotropin in the ninth week of lactation and 2) if electronic estrous detection could replace blood analysis for estimating the onset of normal luteal activity in lactating dairy cows. Holsteins (n = 50) and Jerseys (n = 10) were blocked by breed, lactation number and incidence of retained fetal membranes. Two diets assigned within blocks and fed from parturition until 154 d of lactation were control or control supplemented with 359 mg Zn as zinc methionine, 199 mg Mn as manganese methionine, 125 mg Cu as copper lysine and 26 mg Co as cobalt glucoheptonate. The cows were fitted with electronic pressure-sensing devices in the second wk of lactation. Ovarian structures were determined via transrectal ultrasonography at 7-d intervals from parturition until observation of the first corpus luteum. Blood samples were taken at 7-d intervals and analyzed for plasma concentration of progesterone, insulin and urea nitrogen. Onset of normal luteal activity was identified by progesterone concentrations ≥ 1 ng/mL. Retained fetal membranes increased days to first estrus (detected via electronic estrus detection) in the control cows (54.2 ± 10.2 vs. 81.0 ± 14.2, P = 0.05) but not the supplemented cows (49.7 ± 11.0 vs. 44.0 ± 12.2, P = 0.64). Furthermore, retained fetal membranes increased days to first luteal activity in the control cows (28.1 ± 2.7 vs. 41.8 ±3.4, P < 0.001) but not the supplemented cows (27.7 ± 2.8 vs. 30.0 ± 3.3, P = 0.36). Retained fetal membranes also increased days to first corpus luteum in the control cows (31.3 ± 2.2 vs. 40.2 ± 3.8, P = 0.04) but not the supplemented cows (29.8 ± 2.2 vs. 34.8 ± 3.6, P = 0.23). Days to first service, days open, days from first service to conception, services per conception, milk production, milk components and somatic cell counts were similar for control and treatment cows. Mounts recorded by the electronic system were compared with increases in progesterone from values < 1 ng/mL as an index of luteal activity. Accuracies of detecting onset of normal luteal activity by ≥ 1, ≥ 2, ≥ 3, or &ge 4 mounts of ≥ 2 s duration in 24 h, respectively, were 35.7% ± 0.06 (n = 20 cows), 46.4% ± 0.06 (n = 26 cows), 26.8% ± 0.06 (n = 15 cows), and 23.2% ± 0.06 (n = 13 cows), (P = 0.04). Accuracies of electronic estrus detection in determining estrus after 45 d postpartum by 1, 2, 3, ≥ 4 mounts were 30.1% ± 0.03, 24.5% ± 0.03, 44.8% ± 0.08 and 73.9% ± 0.03 (P < 0.001). Supplementation with complexed trace minerals effectively reduced days to first estrus. Although electronic estrous detection provides benefits in reproductive management, it is not an effective substitute for blood sampling in determining the onset of normal luteal activity in lactating dairy cattle.

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