When I originally looked at this article what struck me was a good presentation of some of the considerations in  feeding a dairy cow. However, while reproducing it, the article did go into greater detail than what I thought after my original read. However, hopefully it may convince some of the Hare Krsna dairymen and others on the importance of diet.  Vd.

By Gordon Macdonald; Ontario Milk Producer, September 1981

Feeding management is a matter of getting the right feed in the right amounts to each cow at the right time. Feeding strategy includes consideration of production, storage, transportation and handling systems for feeds, and proper ration balancing, based on availability, palatability, cost and nutrient content of feedstuffs. While there is no one perfect feeding program for all dairymen, a number of principles relating to nutrition and physiology apply in all systems to a great or lesser extent. A few of the more critical and timely concepts are discussed this article.

The Most important nutritional consideration

While a deficiency or imbalance of any essential nutrient can seriously affect a cow’s performance and health, in general energy is the most critical nutrient. Most of the feed a cow consumes goes to supply energy. Feed energy is the largest single cost in dairying. All body processes including milk syntheses require energy. With feed analyses and proper ration formulation we can do a pretty good job of meeting the cow’s requirements for protein, minerals and vitamins. While we can do this for energy too (in mid and late lactation), we do not know how to get the high yielding cow to consume enough feed energy in early lactation. The extent to
which she fails to meet energy needs has considerable bearing on her health and productivity.

Implications of energy intake limitations

It is tempting to suggest that we should select cows for their feeding intake capacity as well as for milk production. One problem with this is that it is difficult to determining the feed intake of individual cows in modern feeding systems. We know from research and observation however, that dairy cows very greatly in appetite. Several studies at Guelph have demonstrated that superior milk producing cows also tend to have higher feed consuming capacity. The increase in feed consumption by such cows, however, is not as great as their potential for increased milk production. To expect our excellent dairy cows to meet their energy needs in early lactation is perhaps unrealistic, in view of the fact that extra feed intake can often stimulate greater milk production which in turn increases the need for energy.

A small negative energy balance early postpartum is not serious, as cows in moderate body condition have the ability to draw on body energy reserves. We should, however, adopt feeding strategies which avoid extremes of body condition at calving and attempt to minimize the severity and duration of energy imbalance. Obese cows have more calving difficulties and are prone to metabolic disorders. On the other hand, sever underfeeding limits milk output and predisposes cows to ketosis and breeding failure.

Another reason for recognizing negative energy balance in early lactation cows is so we can take this into account when deciding on the protein level of the rations. While the protein reserves of dairy cows are not well defined, we know that they are lower than the energy reserves. Therefore, as our research has demonstrated, feeding adequate protein to meet requirements pays off. Remember, knowing the percentage of a nutrient in feed without knowing the intake of that feed
does not mean much. Cows eat quantities of nutrients, not percentages.

We must continue to develop cows with higher forage intake capacity. In addition to selecting accordingly, we need to study heifer feeding and rearing programs which will develop them to the maximum for forage intake and digestion, because we will likely see higher grain and concentrate costs in the future (relative to forages and economical byproduct feeds). Cows in mid and late lactation can now receive a higher proportion of their energy and nutrients as forage than is frequently practiced, although the value of high quality forages in reducing dependence on concentrates is increasingly recognized.

What limits feed intake?

The dairy cow’s feed intake may be greatly influenced by characteristics of the diet, the animal itself and its environment. Thus, the contribution of forages to meet the energy and protein demand of the high-producing cow may be limited – by dietary factors such as forage quality, its digestibility and energy concentration, by its physical form, and by its type and amount of supplementary feed given. Significant management factors include feed availability and frequency of feeding. Animal factors influencing intake include body size, fatness, pregnancy, stage of lactation and levels of milk production.

...The most common way dairymen maximize feed intake is by feeding the best quality forage possible plus highly digestible concentrate. In 1962, a researcher fed dairy cows long hay free-choice to in addition to a fixed level of concentrate per kg of four per cent fat corrected milk. When dry matter digestibility was increased from 52 to 67 percent by earlier harvest, intake of forage was improved by 40 percent for dry matter and 82 percent for digestible dry matter. The close relationship between forage dry matter digestibility and forage intake is now widely appreciated – though the problems of harvesting high quality immature forage in early June are
still with us.

As dry matter digestibility is increased much above 67 to 70 percent by heavy reliance on grain, intakes of dry matter decrease and intakes of digestible energy level off or decline. Furthermore, for dairy cows fed in excess of 7 to 8 kg of cereal-based concentrates, each kg of concentrate dry matter may decrease forage dry matter intake by 0.6 and give rise to only .04 kg or less extra milk yield, according to a 1980 study. An increase of 0.01 unit digestibility of the forage – say from
0.65 to 0.66 – has a greater effect on energy intake and milk yield than the provision of one additional kg of concentrates. In the future we are likely to see greater dependence on high quality forage and less dependence of concentrates.

Taking advantage of the cow’s digestive system

While each section of the cow’s digestive tract serves important functions, the area of particular concern in the ruminant is usually the rumen. Functions of the rumen include storage, mixing, carbohydrate fermentation, microbial protein synthesis and B-vitamin synthesis. One aim in feeding management should be to encourage efficient digestion of plant cell wall constituents. While cell contents are readily digested by both ruminants and non ruminants, the cell wall components, cellulose and hemicellulose are only digested in the rumen (and reticulum) by micro-organisms living in a favorable environment. For these cellulolytic organisms to grow we
must keep the pH up and avoid an excess of starch-digesting microbes. This is achieved by limiting grain intake and by feeding fibrous feeds in coarse form. Including buffers in the diet may also help, particularly on high grain-corn silage combinations.

On the other hand, grain should be fed in such form as to not bypass the rumen. This is because the capacity of the intestinal tract to digest starch is likely limited and also because an active fermentation of ‘soluble’ or non-structural carbohydrates in the rumen encourages maximum microbial synthesis. The value of high growth rate of rumen microbes, is that it results in conditions leading to maximum feed intake, in better capture of rumen digested protein and subsequently , in a greater amount of microbial protein available in the small intestine to supplement...

At maximum microbial activity sufficient microbial protein is produced and digested in the small intestine to meet the amino acid needs of dry and low producing cows and older growing cattle. But additional amino acids from bypass protein are required for the high yielding young ruminant. Whether the diet supplies sufficient bypass protein or not depends on the relative degradabilities of dietary proteins, as well as other factors such as the level of protein in the diet, the level of feed intake and rate of passage through the rumen. Resistance to degradation is increased as feeds are dried through heating. The extent of change depends on the severity of
exposure to heat (time and temperature).

Protein may also be protected from breakdown in the rumen by treatment with formaldehyde. By achieving a better balance of degradable to non-degradable protein in the rumen, it is possible to increase the amino acid supply available to the cow, resulting in increased milk yield and more efficient use of dietary protein. In Europe, formaldehyde-treated are being used in dairy rations, whereas in North America some feed companies are combining feeds of contrasting protein degradablities to achieve a better balance... Some success has been reported at some extra cost. Systems of describing ruminant needs for amino acids (not just crude protein) and the value of feeds have been developed by various groups and individuals. As we learn more of the amino acid requirements of cows and of the factors including rate and extent of degradation in the rumen and develop better methods for easy prediction of degradation, we will be able to meet the cow’s needs efficiently, use NPN effectively, improve feed intake, energy balance, milk yield and reproductive performance.