Factors Affecting Yield and Composition of Milk

Animal Production – I Information Sheet

FACTORS AFFECTING YIELD AND gradually the production declines. For COMPOSITION OF MILK. Cross-bred and other high yielders it is advisable to have a lactation period of The variation in composition and daily 305 days so that a clear 60 day dry yield of milk is a regular phenomenon in period and a yearly calving programme all milking animals. Broadly, the factors is achieved. The peak yield of the cow is which are responsible for such dependent on her body condition at variations can be divided into (1) calving, her genetical potential, her Physiological, which will be governed by freedom from metabolic and infectious the genetical make up and (2) diseases and the feeding regime after Environmental, such as age, number of calving. Peak milk production plays an previous lactations, pregnancy, nutrition important role in determining lactation status, etc. The dairyman has hardly got milk production, since there is a high any control over the physiological correlation between these two factors. factors but he has some control over the environmental factors. A thorough The rate of decline in milk yield after understanding of the factors that change calving is known as persistency. For the environment of the dairy cattle can high lactation yield cows must have high be used to take advantage of some of persistency as well as high peak milk the changes in milk composition and production. Rate of decline is enhanced yield that occur during a normal by pregnancy particularly with effect lactation. from twenty-second week of pregnancy. This decline attitude at its five and a half 1. Change Occurring during a Normal month of pregnancy may be avoided if Lactation. the cows are bred 60 days after A normal lactation curve. The cow previous calving. reaches her peak yield in about 3 - 6 weeks after parturition, and then

A schematic representation of the lactational curves of milk yield, live weight and voluntary feed intake of cows

Prepared by Tshewang Dorji 1 Animal Production – I Information Sheet There is general inverse relationship Percentage of composition of milk as between milk yield with its protein and well as milk yield vary considerably from fat percentages. As yield increases, the day-to-day. In general excitement, percentage composition of these two oestrus, incomplete milking, and other elements decreases. Lactose content irregularities previous to milking, shows very slight decline towards the disease, under feeding and related end of lactation and ash content shows factors, cause daily variation of milk a very slight increase with advancing yield. Depression in milk yield that lasts lactation. for several days are usually accompanied by higher fat tests as Colostrum. The first milk from the because there is a general inverse mother after birth of the young mammal, relationship between milk yield and fat which has a markedly different test. An incomplete milking fails to composition from that of normal milk. obtain the last drawn milk, which is The most significant difference is the extremely high in milk fat. First drawn high percentage of protein in colostrum. milk, or foremilk may be as low as 1% The composition of colostrum changes milk fat, whereas the last drawn milk significantly into normal milk within 3 - 4 may be as high as 8 - 15%. The milk days following parturition, but it takes yield at the next milking is higher in milk about 15 days for complete fat content normalisation.

Lactation curves of milk fat and protein percentages of Holstein cows

2. Day-to-day Variations.

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Lactational changes in milk yield and composition in dairy cows Animal Production – I Information Sheet

since it contains the leftover milk from the last milking with high fat content from the present milking.

Prepared by Tshewang Dorji 3 Animal Production – I Information Sheet Fat test may again vary up to 1% indicate that they produce approximately between the night and morning milking 85% of the milk produced by a mature when the cows are milked at 14 and 10 cow; the figures for 4 and 5 year old hours intervals. The explanation for this cows are 92% respectively. Cows of variation will involve probably two most breeds are considered mature factors: (1) due to relationship of between 6 and 7 years old. There is pressure to milk and fat secretion, in some variation among breeds. When which milk produced during a long cows are 8 to 9 years of age, a interval and against a higher udder reduction in the level of milk production pressure which has a lower fat test, (2) commences. In addition to the increase due to exercise, which has a tendency of milk production with age, there is a to increase the level of milk fat. slight decrease in the SNF and fat per Consequently the evening milk of cows cent through the fifth lactation, beyond at equal intervals produces milk that has which there is little change. a slightly higher fat test than does that obtained from morning milking. 5. Body Weight. A general relationship exists between 3. Dry Period and Body Condition. the body weight of cows and level of The length of the dry period and the milk production. Larger cows have more body condition at calving are related. udder secretory tissue and larger Cows must be in good body condition at digestive systems. calving and must have had a dry period to attain maximum production. The dry 6. Gestation. period is important for replenishing body A significant reduction of milk yield supplies if the cow is in poor body occurs towards the end of pregnancy. condition at calving and also to Although the exact reason is not yet regenerate milk secretory tissue. known but according to one hypothesis An increase of highest milk yield results it has been suggested that level of with dry period between 50 to 59 days. nutrient required for foetal development Although longer dry periods result in is highest; however, this appears to be higher daily production in the following only 1 to 2 per cent of the daily lactation, the total milk produced over a requirement of the cow. Another series of lactations is not increased. convincing explanation is that of a change in hormone production, in which 4. Age of Cow at Calving. large amounts of oestrogen and It is well known that cows produce more progesterone are released into blood milk as they attain certain ages after stream, which are detrimental to high which a progressive reduction in the level of milk production occurs and milk yield. During fourth to fifth months continues until they die. During first of gestation there is an increase of SNF. lactation at an average age of 2.5 years cow produces approximately 76% of the 7. Temperature and Humidity. milk produced by a mature cow. Severe weather conditions drastically Average figures for 3 year old cows affect milk production. Temperatures Prepared by Tshewang Dorji 4 Animal Production – I Information Sheet between 40 - 75 0F have no effect on the production over two or more years is milk production. In this range (Comfort greatest with the yearly calving interval. Zone), no body processes are directly involved in maintaining body 10. Interval between the Milking. temperature. At a very high temperature As milk pressure increases in the gland, feed consumption is greatly reduced, the rate of milk secretion decreases until there is an increase in water intake, an the pressure in the lumen of the increase in body temperature and alveolus becomes equal to the secretory respiration resulting decrease in milk pressure in the cells lining the alveolus. yield with lowered milk fat, SNF and At this point secretion of milk stops. total solids. Therefore, frequent evacuation of the High relative humidity accentuates the udder is essential for maximum milk problem of high temperatures. production. It has been shown that milking cows three times a day 8. Season of the Year. increases milk production 10 to 25 % Milk production is usually less during the over two times daily milking. Milking four summer because of the higher times a day instead of three results in environmental temperatures and the another 5 to 15% increase in production. prevalence of green-forage scarcity. Thus the season of calving has got a 11. Feeds and Feeding. marked effect on the total production. (a) Changes in Milk fat content. Cows freshening shortly before winter Changing feeding regime can alter fat months produce more total yield than content of milk. The various types of those calving at other times of the year. ration, which can cause a decrease in The increase is probably due to more milk fat percentage, are as follows: favourable temperature and more digestible feeds available during the 1. High concentrate rations winter. 2. Low roughage rations 3. Grass from lush spring pastures 9. Calving Interval 4. Finely ground hay The interval between calving is another 5. Heat treated feeds important management problem the 6. Feeds in pelleted form farmer must deal with. The decision should be made on the basis of individual factors such as feed consumption, labour cost and reproductive efficiency, etc. It has been It has been noted that the above rations shown that it is most profitable for cows decreases milk fat by depressing acetic to calve at twelve-month intervals. This acid production in one hand and on the requires to breed the cows within 2 to 3 other hand by increasing propionic acid months after freshening. More milk can production. Generally the molar be obtained in a single lactation with percentages of VFA in the rumen are: longer calving intervals but total Acetic acid 65% Prepared by Tshewang Dorji 5 Animal Production – I Information Sheet Propionic acid 20% Butyric acid 12% Some of these compounds increase the Others 3% rumen pH and others decrease propionate production and increase Fat depressing rations cause the acetic rumen acetate production. The acid to drop by 10% or more and the drawback in using these substances is propionic acid to increase by similar that most of them are unpalatable and amount. decrease appetite. Another theory behind the milk fat The following types of rations will help to depression states that there is a increase milk fat percentage: reduction in the amount of hydroxybutyric acid in the blood and 1. Feed rations having at least 17% consequently a deficiency in the amount fibre. of this 4-carbon unit that is available for milk fat synthesis. 2. Use a screen that is more than 1/8 A third theory states that the high inch in diameter if ground forage is propionate production causes a used. glycogenic response in the body that suppresses the mobilisation of fat from 3 Feed ungrounded forage at a the tissues and thereby causes a minimum rate of 1.5 hay equivalent to decline in blood lipids that are available 100 pounds of body weight per day. for milk fat synthesis. The fat content of rations normally fed A fourth theory states that fatty acid on dairy cows has no influence on either esterification in adipose tissue is milk yield or milk composition. High fat elevated, which also reduces the feeds results on slightly higher milk availability of triglycerides to the production than low fat feeds due to mammary gland. high energy value of the feeds. Research findings suggest that feeding the following materials can partially (b) Change in protein and SNF content. rectify the fat depression in milk: Changes in protein and SNF contents of milk are less pronounced by 1. Sodium or potassium bicarbonate environmental factors, which the mineral and lactose contents are not at all 2. Magnesium oxide variable under normal farm conditions.

Underfeeding of dairy cows results in a 3. Magnesium carbonate 0.2 % reduction in protein and SNF percentages and a depression in milk 4. Partially delactosed whey yield. Increasing the plane of nutrition to 25% above normal standards results in 5. Sodium bentonite an increase in SNF and protein percentages to the same extent. High level of nutrition results in an elevated 6. Calcium hydroxide. propionic acid production in the rumen. Prepared by Tshewang Dorji 6 Animal Production – I Information Sheet

(c) Change in mineral and vitamin A content is increased when the cow is content. Among minerals, the major exposed to enough of green forages elements (calcium, phosphorus, especially during rainy season. The potassium, chlorine and sodium) cannot carotene present in all green forages be changed by altering the levels of are converted into vitamin A. Vitamin D these elements in the ration of a cow. content of milk can similarly be Trace minerals with the exception of iron increased by providing sun- cured and copper can be increased by roughages or by exposing the cows to increasing the levels of those minerals direct sunlight. in the ration up to a certain extent. For iodine, which is transferred in maximum (d) Changes in specific gravity of milk. amount, it is only 3 to 5 % of the amount When the dairy cow goes off feed there present in the ration appears in milk. is a decrease in the volume of milk produced, accompanied by increase in Among vitamins, some of the fat-soluble the fat, mineral, protein and total solids vitamins, A, D and E can be increased with a simultaneous reduction in lactose in milk through dietary process. Marked and specific gravity of milk. seasonal variation occurs if the vitamin

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