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 - in which the main food is in liquid form, such as milk or a milk replacement. During this phase, the abomasum or true stomach fulfills the main digestive functions.
2. Transition phase: It could be said that this stage begins with the intake of solid food (In Israel it begins from the first day of life). Under intensive management systems, the practice of supplying concentrates (solid food) actually begins during the first days after birth. However, practical experience shows that in the first weeks of life the intake of concentrates is low, although, it should be noted that the supply of concentrates begins to stimulate microbial growth, colonization of bacteria in the rumen, and its functionality. This function will be expressed through the absorption of VFA (volatile fatty acids), the products of fermentation.
The presence of high proportions of fermentable carbohydrates in grains will produce AGV, which is absorbed. Butyric acid (C4) is the one element with the greatest influence on the development of the ruminal epithelium (ruminal papillae).
3. Ruminant phase: once the animal has been weaned, the diet will be based exclusively on solid food (grains and roughage) and water. It is in this stage that the reticulum-rumen will produce large amounts of AGV and bacterial protein, becoming the main organ of the digestive system. In this phase, it must be ensured that the calf can meet the nutritional needs for its maintenance and growth through the ruminal fermentation process.
It should be noted that there are dairy farms where the nutritional regime is based on a supply of total mixed rations (TMR). Fodder such as alfalfa, vetch or clover, (all of excellent quality) one of the main components of TMR.
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. Alfalfa or other legumes such as vetch and clover are usually included in these rations. The legumes used must always be of excellent quality (high protein and low ashes).
WHY LIMIT THE AMOUNT OF ROUGHAGE?
The use of forages in calf nutrition is a topic that has been and is considered controversial. This practice is generally related to physical aspects in calf development such as rumen size growth, the development of rumen muscle tissues or the provision of an abrasive effect that can prevent parakeratosis of the rumen epithelium (ruminal papillae). In those animals where the consumption of finely ground concentrates can reduce the pH and thus produce the abrasive effect mentioned above.
It should be noted that supplying hay and its consumption by the calves in the first weeks of life, generate the filling of the rumen and consequently, there is a decrease in the consumption of other feeds such as concentrates. Due to the low energy values of hay (even in those of excellent quality) and the relatively high requirements of the calves for growth, the consequence will be low growth rates. This energy deficit can be covered by a higher consumption of liquid feeds and as a result, less development of rumen function (lower VFA production) which allows at the time of dewatering to ferment cellulose and hemicellulose, thus using these carbohydrate sources for energy and consequently growth of the calf. Studies where the amount of forage supplied was limited (approximately 12% of DM), or those in which the supply of hay began only after the sixth week of the calf's life, showed no significant difference in results.
It should be noted that the supply of starter concentrate as the only solid feed is easier to handle than the other alternatives discussed.
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 (LW)/day for 3 consecutive days (In Israel there are areas where 2% is reached).
• 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.
• Healthy calves.
The weaning process can be carried out at different times and the common objective is to achieve a sustainable intake of concentrate. At the same time, the amount of milk or milk replacement supplied should be reduced from approximately 4 liters on average to two liters (variable according to the size of the calf) between 7 and 10 days before the scheduled weaning date. The frequency of supply should also be reduced to no more than once a day. Simultaneously, the quantities of concentrate offered will increase and the sustained increase in the intake should be controlled.
The period from birth to weaning will depend on the management programs at each dairy farm and can be done at 30, 45, or 60 days (intake of concentrates of approximately 1kg, three consecutive days). In cases where early weaning is done, the use of pre-starters can be evaluated. This type of concentrate/balanced feed is generally highly digestible, with high concentrations of proteins and fats that theoretically will act as a ruminal accelerator.
It should be noted that the weaning process could generate stress in the calves that is generally expressed as a decrease in the intake of concentrate and therefore a decrease in growth rate. Frequently, stressful weaning situations can increase the calves’ susceptibility to illnesses. This is often expressed as a decrease in concentrate intake and a decrease in growth rate.
This fact forces the producer to strictly monitor the sanitary programs (vaccinations, cleaning, etc.) It is advisable to manage this transition stage by attempting to minimize the factors that can increase the stressful effects generated by the change from liquid to solid diets, or when changes are made from individual to group accommodation
On many of the farms, changes in the components of the nutritional program are associated with changes in the housing of the calf. For example, calves that were grown individually are moved to group housing. This transfer is not recommended before 21 days of age.
In this case, it must be taken into account that when the calves are housed in groups, it is impossible to control individual nutritional intake, hence, the professionalism of the worker in charge is extremely important. It is necessary to be able to distinguish between the sick or healthy, calves (e.g. diarrhea, eye infections, respiratory problems, etc.) and to monitor the effects generated by the milk intake
• Weaning after 60 days. It is advisable to check that the consumption of solid food is constant 3 or more days and reaches a minimum equivalent to 1.2-1.5% of the PV/day.
• Additional criteria for weaning:
o Live weight
o Age at weaning
• Reduce the amount and frequency of liquid food supply (2 liters 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.
• Insofar as the calf must be moved to new accommodations, it is advisable to delay the change for 10 days.
• 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.