Dairy Cattle Production (95314) Dr Jihad Abdallah Topic 6: Factors affecting milk composition

Genetic and environmental factors Milk composition is affected by genetic and environmental factors Genetic factors: - differences among breeds - differences among cows within breeds Environmental factors: - interval between milkings - stage of lactation - age - feeding regimes - diseases - completeness of milking

Genetic factors Breed: Milk composition varies considerably among breeds of dairy cattle: Jersey and Guernsey breeds give milk of higher fat and protein content than Shorthorns and Friesians. Zebu cows can give milk containing up to 7% fat. Variability among cows within a breed Milk components (fat, protein, and lactose) are partially determined by genetic factors. Therefore, these components vary from cow to cow due to differences in genetic makeup of different cows. Selection can be practiced to improve milk composition traits by selecting superior bulls and cows for breeding

Source: University of Arkansas Division of Agriculture http://www.uaex.edu/other_areas/publications/pdf/fsa-4014.pdf

Environmental factors 1. Interval between milkings The fat content of milk varies considerably between the morning and evening milking because there is usually a much shorter interval between the morning and evening milking than between the evening and morning milking. If cows were milked at 12-hour intervals the variation in fat content between milkings would be negligible, but this is not practicable on most farms. Normally, SNF content varies little even if the intervals between milkings vary.

Environmental factors 2. Stage of lactation The fat, lactose and protein contents of milk vary according to stage of lactation. Solids-not-fat content is usually highest during the first 2 to 3 weeks, after which it decreases slightly. Fat content is high immediately after calving but soon begins to fall, and continues to do so for 10 to 12 weeks, after which it tends to rise again until the end of the lactation

Changes in the concentrations of fat, protein and lactose over a lactation of a cow

Environmental factors 3. Age (parity): As cows grow older the fat content of their milk decreases by about 0.02 percentage units per lactation. The fall in SNF content is much greater. Milk protein content gradually decreases with advancing age. A survey of Holstein Dairy Herd Improvement Association (DHIA) lactation records indicates that milk protein content typically decreases approximately 0.02 to 0.05 unit per lactation.

Environmental factors 4. Feeding regime Underfeeding reduces both the fat and the SNF content of milk produced, although SNF content is more sensitive to feeding level than fat content. Fat content and fat composition are influenced more by roughage (fiber) intake. The SNF content can fall if the cow is fed a low-energy diet, but is not greatly influenced by protein deficiency, unless the deficiency is acute.

Environmental factors 5. Disease: both fat and SNF contents can be reduced by disease, particularly mastitis. 6. Completeness of milking: The first milk drawn from the udder is low in fat while the last milk (or strippings) is always quite high in fat. Thus it is essential to mix thoroughly all the milk removed, before taking a sample for analysis. The fat left in the udder at the end of a milking is usually picked up during subsequent milkings, so there is no net loss of fat.

Source: University of Arkansas Division of Agriculture http://www.uaex.edu/other_areas/publications/pdf/fsa-4014.pdf

Environmental factors 7. Level of production: Yields of fat, protein, nonfat solids and total solids are highly and positively correlated with milk yield. Under selection programs that emphasize milk yield, fat and protein yields also increase. However, the percentages of fat and protein in the total composition decrease.

Environmental factors 8. Season: Milk fat and protein percentages are highest during the fall and winter and lowest during the spring and summer. This variation is related to changes in both the types of feed available and climatic conditions. Lush spring pastures low in fiber depress milk fat. Hot weather and high humidity decrease dry matter intake and increase feed sorting, resulting in lower forage and fiber intake.

9. Feeding management practices NFC = nonfiber carbohydrates; NDF = neutral detergent fiber; UIP = undegradable intake protein