public partial class UserControl1 : UserControl
{
    public UserControl1()
    {
        InitializeComponent();
    }

    public int MyProperty
    {
        get { return (int)GetValue(MyPropertyProperty); }
        set { SetValue(MyPropertyProperty, value); }
    }

    public static readonly DependencyProperty MyPropertyProperty = DependencyProperty.Register("MyProperty", typeof(int), typeof(UserControl1), new PropertyMetadata(0));

    private void UserControl_Loaded(object sender, RoutedEventArgs e)
    {
        Label l = new Label
        {
            Content = MyProperty,
            Height = 40,
            Width = 30
        };
        RootGrid.Children.Add(l);
    }
}

<UserControl x:Class="WpfApplication1.UserControl1"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         mc:Ignorable="d"
         d:DesignHeight="300" d:DesignWidth="300" Loaded="UserControl_Loaded">
<Grid x:Name="RootGrid">

</Grid>
</UserControl>

<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApplication1" x:Class="WpfApplication1.MainWindow"
    Title="MainWindow" Height="350" Width="525">
<Grid>
    <local:UserControl1 x:Name="Us" Height="34" Width="139" MyProperty="{Binding Value, ElementName=Sl}"/>
    <Slider x:Name="Sl" Height="30" VerticalAlignment="Top" Width="310" SmallChange="1"/>
</Grid>