Effect of Dietary Manganese on Growth, Reproduction, and Offspring of Beef Heifers

 

S. L. Hansen, C. S. Whisnant, and J. W. Spears

 

Summary

            Manganese (Mn) supplementation of a low-Mn control diet increased liver Mn concentration and serum cholesterol levels.  Heifers supplemented with manganese tended to have better reproductive performance than heifers consuming only the control diet. Calves born to non-supplemented heifers exhibited signs of Mn deficiency, including dwarfism, unsteadiness, and over-extension of the lower jaw. 

 

Introduction

Manganese is an essential trace mineral for ruminants and plays an important role in several functions in the body, including bone formation, enzyme activation and biosynthesis of cholesterol.  Manganese requirements for beef cattle are poorly defined, with recommendations ranging from 20 ppm for growth to 40 ppm for reproduction.  Impaired reproduction in beef cows is one of the major signs of Mn deficiency, with signs often presenting themselves in the calves of deficient cows.  The objective of the current study was to determine Mn requirements for growth, development, and reproduction in beef heifers.

 

Materials and Methods

Eighty Angus (n=40) and Simmental (n=40) heifers, approximately 10 months old and weighing an average of 540 pounds were randomly assigned to treatments.  Treatments consisted of 0, 10, 30, and 50 ppm Mn (from manganese sulfate) added to a basal diet composed of cottonseed hulls, citrus pulp, corn and corn gluten feed that analyzed 18 ppm Mn.  The diets were formulated to meet or exceed all NRC (1996) requirements, with the exception of Mn.   Heifers were housed in a covered facility with slotted floor pens and fed individually via electronic feeders.  Heifers were weighed at 28-d intervals and bled via jugular venipuncture at 56-d intervals.  Samples were collected at 2-h post feeding.  Initial and final weights were the average of weights taken on two consecutive days.  Liver samples were collected initially and on d 98 and 196 of the study for Mn analysis. 

            Two blood samples were taken when the heifers were approximately 12 mo of age to be analyzed for serum progesterone.  These values were used to determine the number of heifers in each treatment group that were cycling.  At approximately 13 mo of age, heifers were synchronized using a two dose Lutalyse protocol.  Heifers that exhibited signs of estrus were bred artificially and observed for heat for 30 days.  Heifers not bred by d 139 of the study were given Lutalyse again and time bred.  Rectal palpation was performed on d 196 for final determination of pregnancy. 

Ten bred heifers from the control treatment and 10 bred heifers from the 50 ppm supplemental Mn treatment were selected to remain on their treatments through gestation.  Heifers were bunk fed by treatments (4 pens per treatment, 2 head per pen) and calved at approximately 23 mo of age.  Birth weights and a blood sample were collected from each calf within 24 h of birth. 

 

Results and Discussion

Weight gain, feed intake, and feed efficiency were not affected by dietary manganese concentration.  Manganese supplementation of the control diet increased liver Mn content (P < 0.05) at both day 98 and 196 of the study (Table 1). Serum cholesterol values were higher for Mn-supplemented heifers than the control heifers. 

            Reproductive performance of the heifers tended to be improved by Mn supplementation (Table 2).  Calves born to control heifers exhibited varying signs of Mn deficiency, including dwarfism, superior brachygnathism, unsteadiness, and slightly domed foreheads.  Calves born to Mn-supplemented heifers were normal.  Control heifers gave birth to significantly smaller calves than Mn-supplemented heifers (P < 0.05).  Whole blood Mn content was higher in calves born to Mn-supplemented heifers than control heifer calves (P < 0.01).

 

Implications

Dietary Mn concentrations of 18 ppm appear to be adequate for growth and development of beef heifers, but may not be adequate for optimum breeding response.  The manganese requirement of gestating beef cattle appears to be higher than 18 ppm for the proper development of healthy calves.

 

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Table 1.. Effects of manganese supplementation on liver manganese concentrations.

 

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Table 2.  Effects of supplemental manganese on reproductive performance of heifers