When the milk protein to milk fat ratio is greater than 1.0, butterfat (BF) is depressed. Legal minimum for BF is 3.3%.
- Problems at the bulk tank -
(Milk fat being produced but low BF% in milk samples):
· Testing and sampling: Inaccurate samples, inaccurate tests, or different tests.
· Theft: Cream skimmed off tanks, or milk stolen from and water added to tanks.
- Cow factors -
· Breed: Generally Holsteins will have lower BF% than Ayrshires, than Guernseys and Jerseys.
· Genetics: 55% of variation in milk composition is due to heredity. Therefore it is important to select for high BF%.
· Age of cows: As cows grow older, BF% decreases.
· Stage of lactation: First three months of lactation BF% decreases, next three months it remains constant, thereafter it increases again. If a high proportion of your cows all calf at the same time, a low BF% problem may occur two to three months later.
· Barren cows: Pregnancy causes an increase in the BF%. If cows are not pregnant, this increase will not occur.
· Level of milk production: Higher production tends to have a diluting effect on BF%. (But not on total BF produced).
· Body condition: Thin cows – underfeeding before calving will lead to a lower BF% after calving.
· Disease: Will generally lower milk fat. Depressed rumen activity and chronic rumen acidosis lowers BF%. Infections of or injury to the udder (high somatic cell counts, mastitis) lowers BF%.
- Environment factors -
· Climate: A slight diminishing of BF% occurs between ambient temperatures of 21º to 27ºC.
· Seasonal effects: Lower BF% in spring and early summer.
· Exercise/Long distances walked: Over-exercise decreases milk yield, increasing BF%, but decreasing the total BF yield.
- Milking practices -
· Milking intervals: The longer intervals between milkings will result in lower BF% than the shorter ones.
· Inefficient milking: First milk obtained from a milking contains about 1 to 2% BF, while milk obtained at the end of milking contains 5 to 10%. The higher the milk yield, the greater this range. Residual milk contains 10 to 20% BF. This means that incomplete milking can lower the BF% of that milking. Also: the higher the milk yield, the higher the quantity of residual milk. Calves being allowed to suckle cows after milking, will remove residual milk high in fat.
· Causes of inefficient milking: Inefficient milkers; incorrect milking procedures; faulty milking machines; stressed cows.
- Feeding -
· Malnutrition: Under nutrition during the dry period or at the beginning of lactation will decrease milk yield and butterfat content of the total lactation period.
· Roughage-to-concentrate ratio: Low-roughage rations will result in a low BF%. A minimum ratio of 40-to-60 roughage-to-concentrate is needed to maintain BF%. If grain or other concentrates make up more than 60 to 70% of dry matter, milk fat depression will occur. Remember that other factors such as rumen pH, propionic acid production, fibre source and digestion, type and physical form of feed, particle size of total ration, buffers, etc. will all influence the effect that this ratio has on rumen fermentation and thus on BF%.
· Grains: The amount of grain should be limited to 3.2kg per feeding and to an absolute maximum of 13.5 to 16kg per cow daily.
· Volatile fatty acids: Feeding too much concentrate and too little roughage will result in production of more propionic acid and less acetic acid in the rumen. Acetic acid is needed for the production of butterfat. If the ratio of acetate-to-propionate levels in the rumen is too low (< 2.2 to 1), body fat will be deposited at the expense of milk fat.
· Fibre: Inadequate fibre in a ration causes low BF%. Quality, quantity and effectiveness of fibre is important. A minimum of 28% NDF (neutral detergent fibre), or 19% ADF (acid detergent fibre), in diet dry matter is required to maximise BF%. The minimum total amount of NDF needed is about 1.2% of body weight. Remember that young lush pastures are low in effective fibre.
· Particle size: Smaller particle size of feed (both forages and concentrates) causes more rapid consumption and ruminal fermentation, shorter chewing time, less saliva, lower rumen pH, and a lowered acetate-to-propionate ratio in the rumen. This results in depression of BF%. Roughages should not be less than 10mm theoretical length of cut, with at least 25% over 5cm long to keep propionate at the desired levels and BF at more than 3.6%.
· Processing of feeds: Processing (grinding, pelleting, steam flaking, rolling, or heating), changes the structure of starch, increasing the ruminal digestion thereof, as well as increasing the microbial production of propionic acid and the risk of acidosis. The result is a lower BF%. An added disadvantage of pelleting is the small, fine particle size resulting from the grinding process.
· Carbohydrates: More than 45% non-fibre carbohydrates in the diet will decrease BF%.
· Protein or sulphur deficiency: May result in decreased BF%. A sulphur deficiency, which would indicate a protein deficiency, is most likely to occur when large quantities of NPN or maize silage are fed.
· Fats in the ration: An excess of ruminally available fat causes low BF% by interfering with fibre digestion and acetic acid production. Certain fatty acids found in fish oils also have an inhibitory action on uptake of pre-formed fatty acids by mammary cells, reducing BF%.
· Rumen pH and buffers: Failing to include buffers in diets high in concentrates, moisture or maize silage, as well as in low-fibre rations, fine and pelleted feeds, and when slug feeding grain, will result in depressed BF%. Both sodium bicarbonate and magnesium oxide should be used in these cases to stabilise rumen pH and to maintain BF%.
· Other additives: Use of Monensin (Rumensin) above the recommended levels will inhibit ruminal micro-organisms that produce acetic acid, decreasing BF%. So check your levels as this product is still recommended to improve feed efficiency.
Erna Penderis, Tammac Consultants, Oct 2000