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Practical sulphur-selenium metabolic interactions in dairy cattle D’Aleo, Lillian Marie Anna


Seventy-one dairy cattle were used to study practical sulphur-selenium metabolic interactions. Upon calving, cows were randomly assigned to one of the following four treatment groups: control (0.35% S, 0.31 mg/kg Se), S supplemented (0.15% S, 0.31 rag/kg Se), Se supplemented (0.35% S, 0.72 mg/kg Se), and S & Se supplemented (0.50% S, 0.72 mg/kg Se). The basal ration was made up of 55% forage as alfalfa cubes, 35% dairy concentrate, and 10% beet pulp. Cows were fed their respective experimental diets until dry off. During the dry period, cows were maintained on a dry cow ration low in Se (0.07 mg/kg Se) for a minimum of 45 days. Two weeks prior to parturition, cows were again assigned to their respective treatment groups. S and Se were supplemented as sodium selenate and elemental sulpher at levels of 0.40 mg/kg Se and 0.15% S, respectively, to yield the final dietary concentrations given above. Milk samples were collected on alternate days from all cows for milk progesterone analysis. Monthly blood samples were taken for plasma Se analysis. Cows from treatments 1-3 were sampled at estrus for plasma LH analysis. Treatment did not influence milk or fat yield. The total daily consumption of alfalfa cubes, 14% dairy concentrate and complete ration was found to be significantly greater during the second lactation for most treatment groups. Beet pulp consumption was not significantly altered in the subsequent lactation or among treatment groups. Response curves for plasma Se response to treatment were found to be signficantly different among treatment groups during the increasing plasma Se phase (months 1-4) and the plateau phase (months 4 - 10). Slope analysis indicated that slopes were similar among treatment groups during both phases of the Se response curve. Regression equations, however, during both phases were different among treatment groups. The Y-intercept for treatment groups 1-4 were 0.08 ± 0.02 (s.e.), 0.07 ± 0.02 (s.e.), 0.09 ±0.02 (s.e.), and 0.08 ± 0.03 (s.e.) mg/kg Se, respectively, with group 3 being significantly higher than treatment groups 1 and 2. During month 4-10, the Se response curve of treatment group 4 was significantly different (p ≤ 0.05) from all other groups. The Y-intercept during the plateau phase for treatments 1-4 was 0.10 ± 0.02 (s.e.), 0.11 ± 0.02 (s.e.), 0.09 ± 0.02 (s.e.), and 0.13 ± 0.02 (s.e.) mg/kg Se, respectively. Dry cow plasma Se levels of animals on treatment groups 1-4 were 0.06, 0.06, 0.05, and 0.07 ± 0.04 mg/kg Se (p ≤ 0.05). Calf plasma Se levels were 0.04, 0.05, 0.04, and .06 ± 0.02 mg/kg Se for calves whose dams were on treatment groups 1-4, respectively (p ≥ 0.05). Days to first service was not influenced by breed or treatment. Days open, calving interval, services/confirmed conception, and calf birth weights were significantly greater for breeds, but these parameters were not affected by treatment group. Cows entering their second lactation were assigned to the same experimental ration as the previous lactation, and were designated as being on experimental treatment groups 5, 6, 7, and 8. Milk progesterone concentrations during periods 0 and 2 of the estrous cycle were not different among treatment groups (p ≥ 0.05). During period 1, milk progesterone concentrations of treatment group 6 were significantly higher than the control group of the first lactation (2.42 and 2.06 ± 0.61 ng/ml, respectively). During period 3 of the estrous cycle, treatment groups 2, 4, 6, 7, and 8 had significantly higher milk progesterone concentrations than the control group (first lactation). During period 4 of the estrous cycle, milk progesterone concentrations of cows on treatment group 6 were higher than those of cows on treatment group 1 (9.42 and 6.56 ± 2.25 ng/ml, respectively). Also cows on treatment group 2 had significantly lower milk progesterone concentrations than cows on treatment groups 4 and 5 (8.43 and 8.45 ± 2.25, respectively). Period lengths of the estrous cycle were not influenced by treatment. Both milk progesterone concentrations and period length (days) were found to be different among the various cycle types identified. Mean cycle length among treatment groups was found to be similar. However, during the second lactation, the frequency of long estrous cycles was 15.6% in both the control and S supplemented group, 3.1% in the Se supplemented group and 12.5% in the S and Se supplemented group. The Incidence of abortion during the second lactation (based on milk progesterone concentrations) was 21.4% in both the control and S supplemented groups, while no Incidence of abortion occurred in the two Se supplemented groups. Milk progesterone concentrations at breeding time were significantly higher for Holsteins than for Ayrshires (2.00 and 1.76 ± 8.81 ng/ml, respectively). Also, milk progesterone concentrations were significantly higher for cows on treatment group 8 in comparison to control cows (2.73 and 1.53 ± 8.81 ng/ml, respectively). Plasma Se concentrations at breeding were also significantly lower in control cows in comparison to cows on treatment group 4 (0.09 and 0.12 mg/kg Se, respectively). A significant treatment by (un)successful breeding interaction for milk progesterone concentrations was observed. Mean milk progesterone levels for cows on treatment group 8 in the unsuccessful breeding group were significantly higher than mean milk progesterone concentration recorded in all other treatment groups. Basal plasma LH levels were significantly lower for Ayrshires in comparison to Holsteins (0.64 and 0.78 ± 0.49 ng/ml). Treatment did not affect LH lag time or basal LH but the preovulatory LH peak was significantly greater in the control grup (50.93 ± 13.09 ng/ml) than in either the S or Se supplemented groups (23.05 and 14.70 ± 13.09 ng/ml, respectively). The incidence of retained placenta during the second lactation for treatment group 5-8 was 22.4%, 1.1%, 0.0%, and 0.0%, respectively. The incidence of abnormal uterus was 18.8%, 10.0%, 14.3%, and 0.0% for treatment groups 5-8. Calving ease was not dependent on treatment group. However, the correlation between calving ease and dam plasma Se (r = -0.6164, n = 12) was found to be significant (p - 0.05), indicating a reduction in the degree of calving difficulties with increasing plasma Se levels. The incidence of mastitis was found to be dependent on treatment group during the first lactation with the highest incidence of mastitis occurring in the Se supplemented group. Somatic cell counts were not different among treatment groups. Other health parameters monitored were not dependent on treatment group. In summary, S does not appear to Inhibit Se metabolism as reflected by plasma Se levels in response to treatment and in view of the response in the productive, reproductive and health parameters monitored.

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