Leukocyte function and health status of calves supplemented Leukocyte function and health status of calves supplemented with vitamins A and E with vitamins A and E

Forty-four Holstein calves were fed milk replacers with varied concentrations of vitamins A and E from 3 to 45 d of age to determine their effects on concentrations of plasma vitamin A (retinol and retinyl palmitate) and vitamin E ( a - tocopherol), lymphocyte and neutrophil functions, and health of calves. Plasma a -tocopherol was unaffected by increased vitamin A supplementation. Fecal scores, and eye and nose membrane responses were improved with increased vitamin A and lower vitamin E concentration, whereas the same treatment tended to reduce neutrophil cytotoxic and bactericidal activity by 6 wk of age. Increased supplemental vitamin E tended to enhance neutrophil functions. However, age appeared to have an effect on response to both vitamins.


Introduction
Previous research has shown improved immune function of lymphocytes with increased vitamin E supplementation to young calves.However, research with other species indicated that absorption of α-tocopherol diminished with increased dietary vitamin A, leading to the hypothesis that increased dietary vitamin A may interfere with absorption of dietary vitamin E in the calf.Therefore, vitamin A may limit availability of vitamin E to enhance immune functions.Many milk replacers contain more than 10 times the NRC requirement of vitamin A and amounts less than or equal to NRC recommendations of vitamin E. This experiment was conducted to determine if 1) increased vitamin A interferes with plasma α-tocopherol concentrations and 2) various concentrations of vitamins A and E in the diet affect lymphocyte and neutrophil functions and other health traits.All concentrations of vitamins that were used reflect concentrations present in milk replacers on the market.

Procedures
Forty-four Holstein calves, blocked by sex and age, were fed colostrum and then transition milk for 3 d.They were then fed experimental milk replacer at 10% of body weight, adjusted weekly.Vitamin A concentrations provided in milk replacers were low (LA; 3,200 IU/lb) or high (HA; 39,900 IU/lb) and vitamin E concentrations were low (LE; 5.1 IU/lb) or high (HE; 25.9 IU/lb).Concentrations of vitamin A and vitamin E reflect those amounts contained in milk replacers.The four experimental milk replacers were designated LA-LE, HA-LE, LA-HE, and HA-HE.Twice daily fecal scores and discharges of eyes and nose were recorded.Calves were weighed weekly.At 0, 3, and 6 wk, blood was sampled for determination of plasma retinol, retinyl palmitate, and α-tocopherol.Blood samples were collected at 3 and 6 wk to determine lymphocyte proliferation and neutrophil cytotoxicity and bactericidal and chemotactic functions (measures of immune health of calves).Concanavalin A was used as the mitogen for lymphocyte proliferation.The cytotoxicity assay was an antibody-dependent cellular-cytotoxicity (ADCC) assay using chicken red blood cells as the target cells.The neutrophil bactericidal assay targeted Staphylococcus aureus.Chemotaxis was measured under agarose with zymosan-activated serum as the chemoattractant for directed:random migration.

Plasma Vitamin Concentrations
Concentrations of plasma α-tocopherol were not affected adversely by increased supplementation of vitamin A at 6 wk (Table 1) but reflected the supplementation of vitamin E. However, α-tocopherol concentrations tended to increase overall with high vitamin A supplementation and were higher (P<.05) at 3 wk.Plasma retinol and retinyl palmitate did not consistently reflect the increased supplementation of vitamin A. Some of the inconsistencies may have been due to a retinol ester that is formed or because of tissue stores (neither measured in our analysis).

Growth and Health
Gain in body weight was similar between treatments for the total 6-wk period (72, 71, 64, and 66 lb for LA-LE, HA-LE, LA-HE, and HA-HE, respectively).The mean fecal score (1=solid, 4=fluid) for the 6-wk period of the HA-LE calves was lower (P<.10)than the scores of both LA treatment groups.The HA-LE group tended to have the lowest fecal score at 2 to 5 wk (Figure 1).The increase for the LA-HE group at 2 wk may explain the decrease in gain of that group that occurred then.The eye discharges increased, beginning at 2 wk for all treatments and remained high through 5 wk (Figure 2).The discharges observed in this study were clear, probably in response to fly irritation.Therefore, an increased discharge was considered a healthy response of the eye membrane.The HA-LE treatment tended to have the greatest occurrence of eye discharges.Total nasal discharges across weeks were greater for the LA-HE treatment (P<.10; data not shown).These discharges were thick mucous that occurred in few calves and for short periods of time and were considered a sign of infection.

Leukocyte Function
No differences in lymphocyte blastogenesis occurred among treatments at 3 or 6 wk (Table 2).Neutrophil phagocytosis and bactericidal activity tended to be lowest at 6 wk for calves on HA-LE treatment.
Significant differences (P<.05) in bactericidal activity occurred between HA-HE and LA-HE treatments at 3 wk.The chemotaxis index indicated a greater response to a chemoattractant at 6 wk for LA-HE-supplemented calves.

Conclusion
Increased supplementation of vitamin A tended to improve responses that rely on a healthy mucous membrane.Simultaneously, the immune functions that utilize vitamin E tended to be improved by increased vitamin E and were inhibited when lower vitamin E and higher vitamin A concentrations were fed.The response of neutrophils to the chemoattractant, although enhanced by HE supplementation, was inhibited when HA was fed simultaneously, indicating possible interference of vitamin A with vitamin E utilization when both are fed at high concentrations.An age effect on vitamin E was seen both in plasma concentrations and leukocyte responses.
row without a common superscript letter differ (P<.05).a,b,c

Table 2 . Cellular Functions Weeks 3 and 6 of Calves Fed Experimental Milk Replacers
Means within row with different superscripts differ ( P<.10); P<.05).a,b,c,d ab cd For description of test see test. 1 Figure 1.

Weekly Fecal Scores of Calves Fed Experimental Milk Replacers. Means Within a Week with Different Superscripts Differ (P<.10). 1 = Solid to 4 = Fluid. Figure 2. Weekly Eye Discharges of Calves Fed Experimental Milk Replacers. Means Within a Week with Different Superscripts Differ
(P<.10).