Creature Companion 2017; May: 40-41.
Anton C. Beynen
Milk for cats
During the suckling period, kittens are entirely dependent on the queen’s milk. In the absence of a
lactating foster queen, orphaned kittens may be hand reared using an appropriate milk replacer.
Milk provides nutrients, including lactose, or milk sugar. The kittens’ intestine produces lactase,
the enzyme that digests lactose, but the capacity falls from birth to weaning.
Many cats love to lap up cow milk, but it is generally considered bad practice: lactose in dairy
products is indigestible and degraded by gut bacteria, leading to diarrhea. This one-sided look at
lactose intolerance paved the way for lactase-treated, hence lactose-free, cat milk. At the same
time, the marketplace offers some dry cat foods featuring lactose-containing milk powder. In those
foods, lactose is simply one of the common indigestible, fermentable carbohydrates present at
harmless or beneficial concentrations.
Research data indicate that adult cats can ingest 6 g of lactose per day without problems, whereas
10 and 16 g cause intermittent and continuous diarrhea. Six g of lactose corresponds with 130 ml
of cow milk. Making allowance for individual sensitivity, 85 ml can be seen as the maximum daily
intake not provoking lactose-mediated diarrhea. This amount must be combined with a base diet
that is nutritionally complete. For a 4-kg cat, commercial food and 85 ml milk, providing 77 and
23% of its daily calorie requirement, form an adequate ration (1, 2).
Food allergy causes skin disorders (itching, self-mutilation) and/or gut problems (vomiting,
flatulence, diarrhea). The risk of milk allergy is very small in cats. In cats, the occurrence of all
food-allergic reactions is not more common than in dogs, and would be affecting less than 0.05%
of the cat population (3), with dairy products accounting for less than 0.01% (4).
It is common knowledge that most well-fed cats enjoy milk. The liking for milk might concern a
preserved mechanism that ensured acceptance of queen’s milk through palatability of the lactose
and/or butterfat constituents. Compared with the solvents alone, cats preferred dilute milk with
added lactose and emulsifier-enhanced water with added butterfat (5).
Milk appetite may reflect a conditioned taste preference. Milk drinking in cats is accompanied by
electroencephalographic activity indicative of diminished arousal (6-8). That response was also seen
in cats with broth intake, but not during water drinking (7). Alpha-casozepine, a hydrolysis product
of casein from milk, may be anxiolytic, but there is no solid evidence that it reduces stress in cats (9).
Cats’ desire for milk is illustrated by the use of milk rewards in some task performance studies (10,
11). Out of 23 foods, only dairy cream and nonfat, evaporated milk masked the distaste of bakers’
paste colorings (12). In a two-choice test (5), adult cats strongly preferred whole, homogenized,
vitamin D fortified milk to the dilute product (20% whole milk, 80% deionized water).
The disaccharide lactose consists of glucose and galactose joined by a ß-(1,4)-glycosidic linkage.
Lactase activity in small intestinal mucosa was high in newborn kittens, but group-mean values in
kittens aged 6-12 weeks and adult cats were about 90% lower (13). Lactose feeding (16 g/MJ
metabolizable energy) did not affect lactase activity in adult cats, while some individuals had high
intrinsic activity (13).
Lactose (6, 10 or 16 g/MJ) in carbohydrate-free diets had an apparent, total intestinal tract
digestibility of almost 100% (14, 15), but lowered fecal pH (15), pointing at extensive fermentation in
the hindgut. Dietary lactose (6 g/MJ) did not influence postprandrial glucose, but brought some
lactose, glucose and galactose in urine (16), urinary galactose excretion equaling about 0.4% of
Cats fed 10 g lactose/MJ had at times diarrhea (14) while 16 g lactose/MJ induced continuous
diarrhea (15). Lactose intake at 6 g/MJ did not harm feces quality and allowed appropriate fecal dry
matter content (15, 17). For a 4-kg cat, 6 g lactose/MJ corresponds to an intake of 130 ml milk/day
or 35% of total calories from whole milk.
Whole milk powder is obtained by removing water from pasteurized, homogenized, whole milk
through evaporation and spray drying processes. In 1962, the US National Academies (18) qualified
two formulas as successful stock diets for growing and/or reproducing cats. The diets, apparently
not inducing diarrhea, contain about 40 energy% dried whole milk (19, 20), or 7 g lactose/MJ.
In the 1930s, Pottenger (21) fed cats on a diet consisting of two thirds raw milk, one third raw meat
and some cod liver oil. The milk provided about 40 energy%. Other cats received either pasteurized,
evaporated or sweetened condensed milk. Raw milk in the diet sustained health, but the other milks
impaired reproduction and caused various disorders. Supporting data come from a contemporary rat
The description of the cat experiment in abstract form (21) lacks details, but suggests that the
applied treatment of milk had generated toxicants and/or had destroyed nutrients, the latter
without abatement by the raw meat ingredient. The impact of modern milk processing on feline
reproduction and health is unknown.
Feeding only unfortified, whole cow milk to cats may cause deficiencies of taurine, iron, zinc,
manganese and copper. Skim milk also falls short of essential fatty acids and vitamins A and D.
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