Beef liver is a nutrient-rich source of protein and iron for dogs, but overfeeding can lead to hypervitaminosis A, so it's best to limit intake to 5% of their diet.
Sardines can provide dogs with essential nutrients such as iron, protein, and fatty acids. However, they are high in fat and may not be suitable for all dogs.
Red meat is a good source of iron for dogs, but it's crucial to watch their fat intake as it is high in fat.
Egg yolks are a nutrient-rich supplement for dogs, but since they are high in fat, it's essential to regulate their fat intake.
Vegetables like spinach, kale, and broccoli contain iron and other essential vitamins and minerals.