Personalized Boy 1st Birthday Cow Number 1 T-Shirt. Make your child's first birthday memorable with our Cow Number 1 design apparel and gifts. So, have you heard the moos? Get your hands on these fun and adorable items today! Wardrobe essential for looking good, 24/7. 5.0 oz., pre-shrunk 100% cotton. Seamless 1x1 rib collar. Shoulder-to-shoulder taping. Double-needle stitched sleeves, bottom hem and front neck. Note: greys are a cotton/polyester blend.