INTRODUCTION

The future growth of dairy herds depends on calf development. Therefore, one of the biggest obstacles facing dairy farmers is ensuring optimal calf development. The calf rearing process (birth-milk) consists of several stages, which determine the production of future milking cow in the herd. Among these phases is weaning. Weaning is one of these stages. This article aims to provide a summary of the considerations that dairy farms should keep in mind when to weaning their calves.

THE PHASES OF THE RAISING PROCESS

Under intensive systems, the stage called Calf Rearing lasts approximately up to 60 days (30-60 days) and has three important phases:

1. Pre-ruminant phase: at this stage, the primary diet consists of liquids, like milk or a milk replacer. The abomasum, or actual stomach, performs the majority of the digestive tasks during this stage.

2. Transition phase: It may be argued that the consumption of solid food marks the start of this stage. In fact, the practice of feeding concentrates (calf starter) starts in the early postpartum days under intensive management systems. Practical experience, however, indicates that little concentrate is consumed during the first few weeks of life. Concentrate availability starts to promote microbial development, bacterial colonization in the rumen, and rumen functionality. The process of absorbing volatile fatty acids (VFAs), which are by-products of fermentation, will reflect this role. These VFAs especially butyric acid helps in early & optimum development of the rumen.

3. Ruminant phase: After the animal is weaned, its diet will consist only of water and solid food, such as grains and roughage. At this point, the reticulum-rumen becomes the primary organ of the digestive system and begins to create huge amounts of VFAs and bacterial protein. During this stage, it is important to make sure the calf can use the ruminal fermentation process to meet its nutritional demands for development and maintenance. One of the primary components of TMR is fodder, such as silage, lucerne, rye grass, maize fodder, or bajra or chari. It is recommended to limit the amount of dry matter forage intake to 12-15%, ensuring that the forage supplied is of high quality and very good digestibility. Lucerne or rye grass are usually included in these rations due to excellent quality (high protein and low ashes).

WHY LIMIT THE AMOUNT OF ROUGHAGE?

One area that has been and continues to be controversial is the use of forages in calf nutrition. This procedure usually has to do with calf development, including the increase of the rumen's size, the development of the rumen's muscular tissues, or the use of an abrasive impact to stop the rumen epithelium from parakeratosis (ruminal papillae). When animals ingest finely crushed concentrates, the pH can drop, which causes the previously described abrasive effect. It should be mentioned that providing hay and having the calves eat it during their first few weeks of life causes the rumen to fill up, which reduces the amount of other feeds like concentrates that are consumed. Because of the low energy values of hay (even of excellent quality) and the calves' relatively high growth requirements, growth rates will be low. This energy deficit can be compensated for by increasing liquid feed consumption and, as a result, less rumen function development (lower VFA production), which allows for the fermentation of cellulose and hemicellulose during dewatering, allowing these carbohydrate sources to be used for energy and, as a result, calf growth. Studies in which the amount of forage supplied was limited (approximately 12% of DM) or when the supply of hay began only after the sixth week of the calf's life revealed no significant difference in results. It should be noted that the supply of starter concentrate as the only solid feed is easier to handle.

HOW AND WHEN TO WEAN THE CALVES?

The criteria that the producer uses to decide when to wean the calves should be practical and simple to measure. It is also recommended that they be based on facts that ensure that the objective of ruminal development and functionality, increase, and growth rate are achieved.

• Measurement of concentrate consumption, ensuring that it reaches a minimum value of 1.2- 1.5 % of live weight day for 3 consecutive days or around 1 kg of calf starter/concentrate.

• Weigh the animal at the time of de-wiring and confirm that the weight has doubled or reached at least a 70% increase (in approximately 60 days) of the weight measured at birth. Other considerations while weaning:

• Reduce the amount and frequency of liquid food supply (2 litres once a day).

• Do not wean sick animals or those that have been sick for a number of days before weaning.

• Avoid activities such as dehorning, vaccinations, etc. during the weaning period.

• Stimulate the consumption of concentrate by a continuous supply of fresh and clean water.

• keep the calves for at least 10 days in the same place.

• When the change of accommodation will be from individual to group systems, it is recommended to do it in two stages in which the first one will be in groups of up to 5-6 calves/group, in which they will stay at least 45 days and then be moved to bigger groups.

• Group housing: should be provided with good ventilation, easy access to feed, and water.