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Animal Science Departmental Report 2004-2005 Return to Beef Cattle articles
Effect of Dietary Manganese Source and
Concentration on Growth, Reproductive Performance, and Manganese Status of Heifers
S. L. Hansen, C. S. Whisnant, L. R. Legleiter, K. E. Lloyd, and J. W. Spears Summary Source and concentration of dietary manganese (Mn) did not affect growth characteristics of growing heifers. Whole blood Mn and liver Mn concentrations were not affected by dietary Mn source or concentration. A greater number of heifers on the control and organic Mn supplemented diets were bred than those fed the inorganic Mn. Introduction Manganese is an essential trace mineral involved in several enzymatic processes in the body. Levels in the body are tightly controlled, with excess Mn being rapidly removed via the portal vein and liver into the bile for excretion (Leach and Harris, 1997). Absorption rates of around 1% have been demonstrated in cattle, therefore, a source of supplemental Mn which is readily absorbed is desirable (Gibbons et al., 1976). Organic minerals have been shown to have increased absorption levels when compared to their inorganic counterparts. It has been observed that Mn from Mn-methionine has a relative bioavailability of 121% compared to a baseline 100% for manganese sulfate (MnSO4). Providing supplemental Mn in the form of a Mn proteinate may allow for increase absorption of Mn, thereby increasing Mn availability to Mn-dependent biological processes. Current Mn requirements for beef heifers are based on limited data and suggest 20 ppm Mn for growth and 40 ppm Mn for reproduction (NRC, 1996). Therefore, the objective of the study was to evaluate the effects of dietary Mn source and concentration on growth, development, and reproductive performance of beef heifers. Materials and Methods Seventy Angus (n = 34) and Angus-Simmental (n = 36) heifers (approximately 9 mo of age, 574 lbs initial BW) were blocked by weight within breed and randomly assigned to one of three treatments. Treatments consisted of a corn-silage based diet (36 ppm Mn) with no supplemental Mn (control), 30 ppm supplemental Mn supplied from Mn proteinate (Bioplex; Alltech, Lexington, KY), and 30 ppm supplemental Mn from MnSO4. Heifers were weighed every 28 d, and liver biopsies for Mn analysis were taken on d 0 and 219 of the study. Jugular blood samples were taken at 56-d intervals during the study. Blood samples for serum progesterone analysis were collected on d 84, 91, 98, and 104 when heifers were approximately 12 mo of age. Heifers with serum progesterone greater than 1 ng/mL on two or more dates were considered to be cycling. At approximately 13 mo of age, heifers that were cycling were synchronized for estrous using a two dose Lutalyse protocol (d 121 and 132). Heifers were bred by artificial insemination following visual detection of standing heat. Synchronized heifers that did not exhibit estrus by d 135 were given a dose of GnRH and time bred. On d 136 heifers were split into treatment groups and put into pastures with bulls for 3 weeks. Three bulls were rotated among the three pastures, with sires in each pasture for a week, to avoid a sire effect. Heifers continued on their dietary treatments while in the pastures. On d 219 rectal palpation was performed on all heifers for final determination of pregnancy. Results and Discussion Weight gain, feed intake and feed efficiency were not affected by dietary Mn source or concentration. Liver Mn concentration did not differ among treatments (Table 1). Addition of Mn to the basal diet increased (P = 0.06) serum cholesterol on d 98 of the study when compared to control heifers. Manganese supplementation increased (P = 0.06) serum cholesterol in Angus but not in Simmental x Angus heifers. There were no differences among treatments in the number of heifers cycling per treatment, or in the response of heifers to a synchronization protocol. Pregnancy rate was affected by dietary treatment (P = 0.02). Pregnancy rate was greater in the control group than in those heifers receiving supplemental Mn, although it is unclear why (Table 2). Implication Results of the present study indicate that a silage-based diet containing 36 ppm Mn is adequate for growth and reproductive performance of beef heifers. References Gibbons, R. A., S. N. Dixon, K. Hallis, A. M. Russell, B. F. Sansom, and H. W. Symonds. 1976. Manganese metabolism in cows and goats. Biochem. Biophys. Acta. 444: 1-10. Leach, R. M., Jr., and E. D. Harris. 1997. Manganese. In: B. L. O'Dell and R. A. Sunde (eds.) Handbook of Nutritionally Essential Mineral Elements. p 335-356. Marcel Dekker Inc., New York. NRC. 1996. Nutrient Requirements of Beef Cattle (7th Ed.). National Academy Press,
Table 1. Effects of manganese
supplementation level and source on liver manganese concentrations of beef heifers
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