Feeding of livestock for efficient growth rate

1. Introduction

Growth in animals is defined as accretion of protein, fat and bone in the body. Although growth typically is measured as change in live weight, nutrient retention is estimated more precisely by measuring empty body weight and its composition. Production economics are judged ideally through carcass weight and carcass quality. Carcass weight gain usually is in a much high percentage during the feedlot phase than during the growing phase of production because dressing percentage increases with maturation and is greater with concentrate rich diets than roughage diets. In a mature body size, body fat percentage seems to be most constant and can be altered genetically and nutritionally. Protein accretion declines to zero when cattle reach their mature body size. Although fat concentration can be reduced by limiting the supply of net energy, rate of fat accretion by finishing steers given access to ad libitum concentrate diets, reaches a plateau at approximately 550 g daily. The protein: fat ratio of carcass can be increased through increasing mature size, administration of hormones, limiting energy intake during the growing or finishing period or slaughtering cattle at an earlier stage of maturity. Energetically, efficiency of accumulation of fat is approximately 1.7 times that of protein. Lean tissue gain is four times as efficient as accumulation of fat tissue because more water is stored with deposited protein than deposited fat,

2. Importance of growth

From birth until weaning to dry off stage, calf undergoes tremendous physiological and metabolic changes. During pre ruminant stage, digestion and metabolism are similar to those of non ruminant animals in many respects. Dietary requirements are best achieved with high-quality liquid diets which are formulated from carbohydrate, protein and fat sources and are digested efficiently. The most critical period is first 2-3 week of life as during this time the calf’s digestive system is immature but undergoes rapid development with regard to digestive secretions and enzymatic activity. Calves raised for purposes other than veal production should be encouraged to consume dry feed at an early age, as this will stimulate development of a functional rumen. A developed epithelial tissue of rumen is responsible for absorption of volatile fatty acids and this development depends on presence of VFA with butyrate being most important.

3. Average daily gains of some beef breeds

4. Role of energy, protein, vitamins and minerals

Energy requirements of calves, like those of other breeds and classes of cattle can be expressed in multiple ways. Regardless of the standard practised, it is pivotal to understand where the major loss of energy occurs when energy-yielding elements of diet undergo digestion and metabolism. If the conversion efficiencies of gross energy to digestible energy/ metabolizable energy and conversion of metabolizable energy to net energy are known, nutritionists can choose the system which best determines their needs. Energy requirements of calves are derived on basis of metabolizable energy; however the requirements and feed composition can be given in net energy and digestible energy units also. Data on energy requirements are formulated for replacement calves fed only milk or milk replacer, calves fed milk and starter feed or milk replacer and starter feed. The amount of liquid feed offered to replacement calves is restricted to encourage intake of dry feed, but calves reared for veal are fed milk or milk replacer at near ad libtum intakes to have faster weight gains. Energy is considered first in diet formulation. Energy intake can determine the calf’s ability to utilize other nutrients to a much large extent. Energy requirements are affected by mature body size, physical activity and environmental temperatures.

Little information is available on the protein requirements of young calves weighing less than 100 kg. The requirement is partitioned into 2 components: maintenance and gain. Maintenance constitutes obligate nitrogen losses in the urine and faeces, whereas gain restricts to N stored in tissues. Microbial protein supplies around 50% of protein and amino acid needs. Protein deficiency is most commonly seen in calves grazing mature forages or low-quality hays, or straw. Less than 7% CP is not enough to provide sufficient ruminal nitrogen for microbes, resulting in reduced intake and digestion of forages.

In case of growing animals, calcium and phosphorus play a pivotal role in the diet. If not consuming adequate amounts, various deficiency disorders can develop, e.g., rickets & osteomalacia in young animals and adults respectively. Cobalt is needed by microbes to synthesize vitamin B₁₂. Where iodine is low in the soil,  use of iodized salt would be the most convenient way to provide I₂. Forages are relatively high in many minerals (e.g., Cu, Fe, Mg, Mn,etc.), but grains are usually very low in many minerals. Adding mineral mixture as an important component of diet will serve to prevent occurrence of any disorders.

Vitamins-sun-cured forages contain large amounts of vitamin D, vitamin E, and β- carotene. Vitamin A can be stored enough for 2 to 4 months, but would be depleted quickly without regular supply of dietary Vitamin A. Once calf is weaned to dry feed, there is no need to supplement water soluble vitamins in the diet, as the micro organisms in the digestive tract can synthesize ample amounts to meet the needs of calf.

4. Conclusions

Although growth rate depends on genetic makeup of the animals, nutritional and hormonal factors can play a major role in limiting growth rate and altering mature size, reducing or increasing fat content of the carcass at a given age. Heavy mature weights are not desirable for ruminants maintained for reproduction. Growth stimulants or depressants and agonists altering body size and composition may prove beneficial in enhancing production efficiency in cow herd and in finishing animals

Neeti Lakhani¹ and Anant Simran Sidhu‘

College of Veterinary Science, Rampura Phul, GADVASU, Bathinda, Punjab, 151103