Since 1944, the National Research Council has issued basic nutritional guidelines and recommendations for many farm animal species.
In 2001, the NRC published their seventh revised edition of their dairy cattle nutrition publication.
This publication includes several significant revisions to the basic nutritional requirements for dairy cows. Most notably, the protein/amino acid supply and requirement system was completely overhauled.
Contents
Amino Acids and Proteins
Dairy cows rely heavily on amino acids (AAs) as their primary nutrient. In fact, dietary protein has been recognized as one of the original six primary nutrients for over 150 years.
Furthermore, rumen microorganisms require AA for protein synthesis. As such, protein deficiency can lead to decreased fermentation rates in rumen and ammonia losses from manure [7, 8, 9, 10].
Nutritionists have begun to recognize the significance of rumen-protected AA (RP-AA) for dairy cows. RP-AA can boost milk protein and fat concentrations.
Lapierre and colleagues [14] proposed that the nutritional requirement system for lactating dairy cows be separated from the substrate-defined AA theory by including variable efficiency levels of absorbed essential AA. This shift of focus from providing endless supplies of grains and other feeds to demand-driven systems that take into account a cow’s capacity for altering metabolism.
While CP remains an essential nutrient in dairy cattle ration formulation, recent research has shifted how protein is utilized. These include discovering that AA and ammonia are crucial nutrients for dairy cattle, as well as realizing the need for moderation when using CP.
Carbohydrates
Carbohydrates are the primary energy source for dairy cows and ruminants, accounting for 75% of plant dry matter and serving as precursors to milk glucose and fat production.
Factors such as forage quality, grain or hay silage quality, feeding procedures and management practices all affect rumen carbohydrate digestion. A poorly designed ration formulation that reduces digestibility can significantly decrease nutrient intake and performance for dairy cattle.
Carbohydrates can be divided into structural carbohydrates (cell wall and hemicellulose) and non-structural carbohydrates (soluble sugars, starches, and neutral detergent fibers). Structural carbohydrates are highly digestible and degrade rapidly in the rumen.
Minerals
A comprehensive mineral program can have a significant effect on fetal development, immune function, bone and muscle formation, fertility, milk production, skin, hair and hoof quality. Trace minerals like cobalt, copper, iodine, iron manganese selenium zinc are essential elements in dairy cattle nutrition for optimal growth and health.
Zinc deficiency can have a negative impact on fetal development, rate of gain, milk yield and body condition. Anemia and inadequate zinc intake may also occur which will slow wound healing and increase the likelihood of foot rot.
Calculating a cow’s trace mineral maintenance requirement can be challenging. In 2001, the NRC defined this need as “endogenous faecal losses and insensible urinary losses.” Unfortunately, this definition does not adequately account for many essential trace minerals that act as cofactors to enzymes necessary to ensure health.
Vitamins
Dairy cows require a balanced diet that provides carbohydrate, protein, fatty acids, vitamins and minerals to produce high quality milk. Carbohydrates are the primary source of energy for dairy cattle; making up more than 70% of their dietary intake.
Cattle typically obtain most of their protein needs from microbial protein, which has a high biological value and is easily digestible. Therefore, diets should be designed to promote optimal microbial growth and minimize the need for additional sources of protein.
Vitamins in the diet are vital for healthy growth and reproduction. Not only that, but they provide protection from illness as well as improved rumen function.
Supplementing minerals and vitamins should be done through the grain mix or total mixed ration, so that an appropriate amount is given to all heifers, dry cows, and milking cows. Studies have indicated that cafeteria-style or free-choice mineral supplements often result in inadequate intake.
