PHYSIOLOGICAL NEEDS OF LIVESTOCK
The physiological needs of livestock vary with class, age, and breed of animal. Lactating cows and first calf heifers have high demands in terms of digestible energy and crude protein. To maximize gains, yearlings and steers require good quality forage. Dry cows do not need as high a plane of nutrition.
Larger breeds have higher forage requirements based entirely on body size. This becomes a more important factor during lactation. Breeds producing more milk and larger calves have elevated energy requirements and may require supplementation or better quality forage if they are to maintain milk production and be ready for re-breeding.