By Margaret Quaassdorff & Casey Havekes, Cornell Cooperative Extension Regional Dairy Management Specialist
It is widely accepted as an industry standard that calves should double their birth weight by 60 days of age. To accomplish this target, or even exceed it, calves must receive a sufficient supply of required nutrients. Often this results in calves being fed high amounts of milk and/or milk replacer. An important consideration when feeding high planes of nutrition is that the more liquid that goes into the calf, the more liquid there will be coming out. Loose manure from calves on a high milk diet can easily be confused with nutritional scours. The first objective of this article is to help calf raisers understand and calculate nutrient requirements. Secondly, the article strives to help calf raisers understand the difference between nutritional scours and normal loose manure, and if action is necessary to improve the health and well-being of these calves.
Energy Requirements of Calves:
A calf’s nutrient requirements can be broken down into the following categories: energy, protein, vitamins, and minerals. Like all growing animals, the nutrients provided to the calf will first go towards maintenance and then any remaining nutrients will go towards growth. So, you may be wondering how we should feed these calves to ensure there are sufficient nutrients available to meet our growth targets. That is an excellent question, and we will attempt to walk you through the steps below to calculate energy requirements, specifically. Please note, that your local Extension Support or trusted advisors are also available to help you. Maintenance requirements for calves can be calculated with the following equation:
MEmaintenance Mcals = 0.1 x BW(kg)0.75
If we take a 41 kg (~90 lb) calf, for example, her maintenance requirement is going to be 1.61 Mcals metabolizable energy (ME)/day. An important note is that this equation does not consider temperature or breed which are both very important when calculating energy requirements. During cold weather, calves require additional energy to meet their maintenance and growth requirements. Specifically, for every °C the temperature drops below the calf’s thermoneutral zone (15°C or 60°F), the calf’s energy requirement is going to increase by ~0.03 Mcals ME. This may not seem like a big increase, but if you think about a very cold winter day where the temperature is -15°C (5°F), that calf’s energy requirement for maintenance alone is going to be increased by 0.9 Mcals ME (i.e. 0.03 * 30°C difference between thermoneutral temperature and outside temperature).
So now that we understand maintenance requirements, we need to calculate how many additional nutrients are required to achieve growth targets. The energy requirement for growth can be calculated with the following equation:
MEgrowth Mcals = [0.84 * BW(kg)0.355 * (ADG (kg/d)1.2)]
If we take that same 41 kg calf and we would like for her to gain 0.8 kg/day, then her growth requirement is going to be 2.4 Mcals ME. Now, if we combine her growth and maintenance requirements (assuming it is a nice spring day with a temperature of 16°C or 61°F), we get a total energy requirement of 4.01 Mcals ME. Once we have a total energy requirement for that calf, we must calculate how much milk or milk replacer is required. We can calculate energy content of milk replacers based on a series of formulas – please reach out to Casey or Margaret, or a trusted advisor if you need help calculating these values. A general assumption is that most milk replacers will have an energy value of ~4.2 – 5.0 Mcals / kg of dry matter (DM), while Holstein whole milk is closer to 5.3 Mcals. If we take a 28:20 milk replacer that is supplying 4.74 Mcals ME / kg DM, we can then calculate how much we need to feed to meet the requirement of 4.01 Mcals by dividing 4.01 Mcals (required) by 4.74 Mcals (supplied). By doing this simple calculation (4.01 / 4.74), we get a value of 0.85. This means that this specific calf requires 0.85 kg of this specific milk replacer to achieve her maintenance and growth requirements. Calculating feeding rates to meet requirements is important; however, it is only one piece of the puzzle. Another important aspect relates to management of these milk-based diets. The remainder of the article is going to discuss key management practices for feeding calves milk and/or milk replacer diets, particularly those on a high plane of nutrition.
Please note, the calculations above are specific to °C and kg, thus °F and lbs cannot be substituted into the equations.
Loose Manure vs Nutritional Scours:
Normal loose manure is often confused with nutritional scours. It is important for those who raise calves to be able to distinguish between the two. True nutritional scours is diarrhea (excessively and abnormally loose or watery stool), and has negative consequences for the health and growth of our calves. It can be caused by a number of management practices associated with the composition, cleanliness, mixing, prepping, or delivery of milk or milk replacer. It differs from normal loose manure that is typical in calves fed a high plane of nutrition (10+ liters/day) of properly mixed and delivered milk or milk replacer. Nutritional scours is the result of digestive upset, not merely volume of milk going through a calf’s system. More milk in means more liquid manure coming out. A calf with loose manure that is otherwise alert, healthy, growing, and showing no signs of dehydration (i.e. sunken eyes, poor suckle reflex, lethargy, depression) is not suffering from nutritional scours.
Figure 1. This is normal manure from a calf on a high plane of nutrition. Without knowing further background information about the calf, it could also be a sign of nutritional scours.
Causes of True Nutritional Scours:
How to Troubleshoot:
Figure 2. Evaluate dehydration in calves using overall appearance and the “Skin Tent Test”