It is common practice to have a calving or lambing season during or shortly before the onset of the raining season. The requirements of female animals for protein, energy, minerals and vitamines increase dramatically during late gestation (the 3rd trimester) and early lactation. Especially ewes that are pregnant with or suckling twins have significantly higher nutritional demands during these production phases, which necessitates that good quality grazing is available.
Not only do the animals have a higher demand in terms of the amount of nutrients required, but the quality of specifically the proteins required during high production phases (eg late gestation and early lactation) is also of crytical importance. Amino acids are the building blocks of proteins and when one or more of these are deficient it will limit production. Often, the nutrient composition in natural grazing is imbalanced or deficient in one or more nutrients and cannot supply in the total demand of high producing animals. Climatic conditions (rainfall, temperature, humidity etc.) also influence the chemical composition of the grazing. The nutritional value of the same piece of veld or pasture can differ substantially for corresponding periods in different years. These differences are even more substantial between differents seasons.