Non-mastitic Alterations in Goat Milk

The presence of blood or unpleasant flavors in goat milk decreases the desirability of milk and cheese for human consumption. Decreased butterfat is another common but serious problem for commercial producers of fluid milk or cheese.

Bloody Milk

Sometimes goat milk is slightly pink or a red s^dm^ε^nt collects on the bottom of the milk container in the refrigerator because of ruptured blood vessels in the udder. The skin over the udder is not cold ot blue, and the goat is not syst.emica.lly ill (in the absence od othet disease conditions). The need to distinguish bloody milk from gangrenous mastitis often prompts peHor- mance of a milk culture. One author advises telimg the owner to call for results in five days, because by then the blood has usually disappeared from the milk (Baxendell 1984a). The irrelevancy of a non-aureus staph species to the condition should be discussed in advance if the owner is to obtain maximum assurance from the culture test results.

If the goat has kidded recently, the possibility of hypocal­cemia could be investigated. Some veterinarians adminis­ter vitamin K or other blood coagulant therapy. The results have not been compared with the self-cure rate. The envi­ronment should be examined for sources of trauma to the udder, including high door sills and rough milkers, be they hands, machines, or butting kids.

Off-Flavored Milk

Off flavors or milk taint problems must be considered in relationship to the intended use for the goat milk. In Scandinavia, the aim is to produce certain cheeses with a characteristic “goaty” flavor. To achieve this flavor, pro­ducers may feed more dry hay or store the milk for as long as 42 hours before processing into cheese. They also can use genetic selection, as the hereditability coefficient for goat flavor in Norwegian goats has been calculated to be 0.25 (Trodahl et al.

Evaluating Off-Flavored Milk

While investigating a milk flavor problem, the ∣∣wner needs to determine if the flavor is present at mllkmg ot if it develops with storage. Is the milk tainted from one half (suggestive of mastitis) or from both halves of one goat? Is the milk from certain pairs of goats mcompat- ible, such that mixing produces the problem? Are many goats involved? If the owner has not yet evaUuated the flavor from each half of each goat separately, immediately after milking, the veterinarian should at least suggest pasteurization to avoid any danger of the zoonotic diseases listed in Table 14.2. If a single goat it involved and if mastitis can be ruled out, the goat can then be kept in a stall and fed only weed- free hay for several days. If the abnormal taste disappears, it was probably caused by feed. The goat is then introduced again to one feed at a time and then one pasture at a time until the source of the offending feed or weed is identified (Baxendell 1984c). See also an investigation scheme by Matthews (2016).

Milk Lipase and Its Effects

Goat milk contains an intrinsic milk lipase (e.g, lipo­protein lipase, LPL) that is capable of causing enzy­matic hydrolysis of milk fat and an increase in free fatty acid content of the milk, including the medium- chain fatty acids responsible for goat flavor. Microbial action can also contribute to lipolysis. Approximately 46% of the LPL is to be found in the cream portion of goat milk. The enzyme is responsible for both “spontaneous lipol­ysis” (initiated by cooling fresh milk) and “induced lipolysis” (initiated by mechanical or thermal treatment of milk).

There are great differences between goats in LPL activi­ties and in milk lipolysis. In one study (Chilliard et al. 1984), the most susceptible sample released 26 times more free fatty acids in 24 hours than did the least active sample. In France, the level of lipolysis is approximately four times greater in milk collected during the summer months (mid­lactation) than in the winter (LeMens 1987). Evening goat milk has relatively more LPL than morning milk. Other factors that might be involved in the process have been explored (Chilliard et al. 2003). Dairy processing plants can determine acid degree values (ADV) as an objective deter­mination of rancidity. At least for cow milk, a soapy-bitter rancid flavor is expected if the ADV is more than 1.0 (Ishler and Roberts 2002).

When an individual goat's milk is subject to spontaneous lipolysis, the milk initially tastes normal, but deteriorates rapidly with storage in the refrigerator. The problem can be controlled by heating the milk to 57 °C (135 °F) immedi­ately after collection to partially inactivate the enzyme. This process is called heat treatment, to avoid upsetting owners who have a strong aversion to anything suggestive of pasteurization. Unless the milk will be made into an aged cheese (more than 60 days), pasteurization is still

Box 14.1 Causes of Abnormal Flavors in Goat Milk

Herd Problem

a) Hygiene - buckets should be chemically sanitized or scalded to avoid introduction of psychrophils that multiply in refrigerated milk. Stainless steel, glass, and enamel are preferred over other materials because of ease of cleaning. Clean, well-ventilated barns avoid inhalation of ammonia and other malodorous agents.

b) Milk- handling procedures - milk should be rapidly cooled and stored in covered containers in the refrigerator. Exposure of milk or cheese to copper or iron metal, sun - light, or fluorescent light results in oxidized flavors that are variously described as “cardboardy” “metallic,” or “oily.” Copper tubing should be avoided in the milkhouse, espe - cially if water pH is less than 7.0.

c) Nutritional considerations:

1) Cobalt deficiency - expect a response within a few days after providing a mineral block containing cobalt or after injecting vitamin B₁₂.

2) Vitamin B₁₂ deficiency secondary to helminthiasis has been proposed as a frequent cause of tainted milk (Mews 1987).

3) Vitamin E deficiency- without vitamin E's antioxi­dant effects (e.g., winter feeding), oxidized flavors may develop. Based on recommendations for cat tle of daily supplementation with 1000-7000 IU of vitamin E, feeding an additional 400 IU vitamin E/day/goat for one to two weeks could be tried (Ishler and Roberts 2002).

4) Unsaturated fatty acids in milk are more suscepti­ble to oxidation and may be limited by decreasing fat (full-fat soybeans, whole cottonseed, added fats) in the diet and by increasing the forage -to- concentrate ratio.

5) Inadequate dietary protein may lead to weakened fat globule membranes and thus to rancidity (Ishler and Roberts 2002).

6) Feed or weed flavors - plants incriminated include silage, cabbage, turnip, fresh alfalfa, ragweed, goldenrod, honeysuckle, buttercups, blackberry, and grape leaves (Lovegrove 1990).

7) Garlic preparations used for possible anthelmin­tic effect.

8) Drugs such as anthelmintics that are secreted into milk.

d) Buck odor - housing the buck with the does usually has not caused flavor problems unless the milk is not properly handled.

Individual Goat Problem

a) Genetic flavor - the reverse of the Scandinavian approach suggests selecting for does with a good fla vor to their milk.

b) Spontaneous lipolysis - abnormal flavor develops under refrigeration.

c) Ketosis.

d) Mastitis.

e) Feed flavors - strong-flavored feeds should be fed after milking, not within the four hours preceding milking.

Table 14.2 Zoonotic diseases potentially transmitted by raw goat milk.

advised. Pasteurization, and even boiling, do not com­pletely inactivate lipase in goat milk (Jandal 1995).

Low Butterfat

The normal butterfat concentration of most European dairy goat breeds under temperate conditions is approxi­mately 3.8%, whereas Nubians and Pygmy goats Iradi- tionally give a richer milk (Jenness 1980; Haenlein and Caccese 1984). Goat milk fat is higher in medium-chain triglycerides than that of cow milk (Sanz Sampelayo et al. 2007). The same authors review the effects of diet on the fatty acid profile of goat milk. Genetic selection for high-volume secretion of milk without consideration of solids composition gradually causes decreased butter­fat concentrations. As butterfat levels decrease, there is a decrease in cheese yield. Also, the milk may no longer achieve legal standards for marketing.

Dietary Roughage versus Concentrates and Dietary Fat

One of the most common causes of low butterfat is a ratio of dietary concentrates to roughages of more than 2 : 1.

How the concentrates are distributed to the goat also affects rumen acidosis and butterfat production. Thus, roughage should be fed before grain in the morning. Dividing the concentrate portion of the diet into more than two meals per day is also helpful. Long alfalfa hay supports higher butterfat concentration than a chopped dehydrated product (Morand-Fehr et al. 1999), assuming the goats eat more than the leaves of the alfalfa. Additional discussion is provided in Chapter 19.

Excessive dietary fat can decrease butterfat production by coating rumen fiber and interfering with its digestion. However, rumen-protected fats at up to 8% of the diet increase butterfat without detrimental effects on milk pro­tein production (Morand-Fehr et al. 2000). Contrary to what occurs in cows, supplementation of the goat's diet with vegetable oils rich in polyunsaturated fatty acids does not decrease butterfat production (Sanz Sampelayo et al. 2007; Toral et al. 2015).

Use of Buffers

Roughage is more effective than sodium bicarbonate in ele­vating ruminal pH and acetate molar fraction (Hadjipanayiotou 1982). However, supplementing a low-roughage diet with NaHCO₃ (at 4% of the concentrates) significantly increases milk fat production. The improve­ment is noticeable two to three weeks after incorporating the buffer into the diet (Hadjipanayiotou 1988). Supplementing the low-fiber diet with bicarbonate at 1-1.5% of total dry mat­ter intake tends to increase butterfat, and adding probiotics may also be beneficial (Morand-Fehr et al. 2000).

Environmental Temperature

High environmental temperatures contribute to low but­terfat through their effect on roughage consumption (Devendra 1982). The heat-stressed goat eats less roughage or preferentially selects the more digestible portions of the roughage available. This decreases the heat of digestion lib­erated in the rumen, but also decreases acetate production, and thereby butterfat synthesis. Providing good ventila­tion, plentiful water, and multiple smaller meals helps to alleviate the effects of environmental temperature.

Other Techniques for Increasing Butterfat

Feeding larger quantities of dried brewer's grains has resulted in increased butterfat production (Sauvant et al. 1987). More complete milkout also increases the butterfat percentage (Morand-Fehr et al. 1999).

When all else has failed, or often long before appropriate changes in management have been made, a producer may purchase several Nubian goats to raise the herd butterfat concentration to exceed the minimum legal limit in the state or country.