|Livestock Research for Rural Development 2 (3) 1990||
Citation of this paper
On milk yields and calf rearing
39 Hunshelf Park, Sheffield, South Yorkshire S30 5BT, UK
and E R Orskov
Rowett Research Institute, Bucksburn, Aberdeen AB2 9SB, UK
Experimental results reported in the literature indicate that the advice often given to farmers in developing countries to wean calves early in order to increase the amount of saleable milk is inappropriate. Suckling can increase milk yields and may reduce the incidence of mastitis, as well as prolonging lactation. Calves allowed to suckle for limited periods are healthier and grow faster than those reared on substitute milk feeds. Bos indicus breeds and even their F1 crosses with European breeds may not let down their milk unless stimulated by suckling their calves briefly prior to hand or machine milking.
Key words: review, suckling, milk yield, milk substitutes, artificial rearing, calf health, resource-poor farmers, Bos indicus
In his book "The Calf: Management and Feeding", Roy (1970) states "In general, it will be more economic to wean at the youngest age possible, commensurate with achieving a low mortality and the desired weight gain". Similarly, Fishwick (1962) writes 2Milk is an expensive food... and in commercial herds it is desirable to reduce to a minimum the amount of whole milk fed to calves. This can be done by using a milk substitute."
Are these recommendations sensible from the point of view of resource-poor farmers in developing countries? This paper briefly reviews the main considerations, some of which were discussed by Preston (1983).
Substitute milk foods
The practice of very early weaning and substitute feeding has been developed in association with large dairy herds, managed in conditions vastly different from the small units of most Third World farmers. Substitute milk diets for calves are generally based on dried skim milk, a by-product of large-scale butter manufacture, the butterfat being replaced by such fats as lard, tallow or coconut oil. Other ingredients may include hydrolysed cereal starch, ground oilseeds, blood and bone flours, fishmeal and antibiotics (Petersen 1950; Roy 1970).
The regular supply of a nutritionally adequate calf milk replacer presupposes dependable sources of the various ingredients and high technical skills and equipment for blending them, e.g. for the homogenization and stabilization of fat. Miller (1979) notes that "the requirements for a good milk replacer are more rigorous than for any other type of food normally used by cattle".
Above all, substitute feeding assumes that the farmer gains enough from the sale of milk not drunk by the calf to pay for the feed. Where ingredients are expensive because of scarcity or transport over a long distance, this may not be possible.
The effect of suckling on milk yields
There is in fact much evidence from work carried out on large-scale dairy farms to show that suckling can increase milk production (Everitt et al 1968; Everitt and Phillips 1971; Walsh 1974; Chandler and Robinson 1974; Laoser 1975; Peel et al 1979; Thomas et al 1981; Copeman and Phillips 1983; Perez et al 1984). These studies were carried out on herds in New Zealand, Australia, Ireland and France, their prime aim being to test the feasibility of rearing three or four beef calves per cow, in order to utilize the milk which is surplus to the requirements of creameries during the season of maximum production. Estimates of milk yields - based on the differences between the calves' weights before and after suckling - exceeded the yields of control cows milked by machine. Smith et al (1973), on the other hand, observed no increase in milk fat production (milk weight was not recorded) by cows grazing pasture during a period of drought, which suggests that a low plane of nutrition may limit the capacity to respond to suckling.
In several investigations, milk production by cows sucked for up to 12 weeks continued to exceed that of control animals for some time, even after weaning (Everitt and Phillips 1971; Veitia and Simon 1972; Kaiser 1975; Fulkerson et al 1978; Peel et al 1979).
The percent increase in post-weaning yield appears to depend on the duration of suckling, a minimum of four weeks being necessary for significant response (Peel et al 1979), but no differences were found between cows which had been sucked for 6, 9 and 12 weeks (Kaiser 1975). When the cows were on a restricted diet, there was no effect on post-weaning milk production (Kaiser 1975), again suggesting that a minimum plane of nutrition is necessary for the response.
The capacity to respond to suckling varies with the breed of the cow. Ugarte and Preston (1972) compared pure Holstein with Holstein x Brahmin F1 cows. They were either only milked or were allowed to suckle their own calves for 15 to 30 minutes twice daily, shortly after milking. In the Holsteins, the increase in total milk production in response to suckling was 45%; in the crossbreds, it was 73%. This work showed that, although the yield of saleable milk may be reduced when the calf remains continuously with its dam, restricted suckling twice daily can so increase production that the quantity available for sale is unchanged or even increased.
Paredes et al (1981), using Brown Swiss x Holstein cows in a similar study, confirmed this. Their control group averaged 14 kg/day whereas the sucked cows on average gave 16 kg/day at milking plus 5 kg/day taken by the calf.
The study of Ugarte and Preston (1972) is particularly relevant to the needs of resource-poor farmers because, in some of the trials, the cows were hand-milked. Since hand-milking tends to empty the udder less completely than machine-milking and since milk secretion is stimulated more when the udder is thoroughly emptied, the effect of suckling after milking is likely to be greater in hand-milked cows.
Possible effects of suckling on prolactin levels
The presence of the calf during lactation may have effects additional to better udder evacuation. Tactile stimulation of the udder and teats, by the calf or by hand, promotes the secretion from the cow's pituitary gland of prolactin (Johke 1969; Tucker 1971; Kiprowski et al 1971; Reinhardt and Schams 1974). The additional stimulus of suckling after milking increased prolactin release in Friesian heifers (Fulkerson et al 1978). This extra stimulation may be even more effective in the indigenous cattle of developing countries than in western dairy breeds, which may have been selected unknowingly but effectively for high prolactin release in response to relatively little stimulation.
It is conceivable that, in some tropical breeds, the presence of the calf triggers a reflex prolactin-releasing response (which might be established during the first days of lactation) comparable to the calf-dependent release of oxytocin necessary for milk let-down (Williamson and Payne 1959; Mahadevan 1966). Again, such effects are less likely to occur in highly selected dairy breeds than in undifferentiated general purpose breeds.
Suckling and the health of the calf
Restricted suckling after milking is unlikely to reduce and may increase the amount of saleable milk from adequately fed animals. At the same time, the health and growth rate of the calves are likely to be better if they are fed milk rather than milk substitutes. Miller (1979) states: "Although calves can be raised with few deaths on a good milk replacer, often mortality may be somewhat higher than when whole milk is fed". Aside from being nutritionally appropriate, milk has more specific protective properties (reviewed by Bourne 1977 and Powell et al 1985).
Like colostrum, milk contains antibodies, including important ones directed specifically against organisms with which the cow has been infected and which may be present in the particular local environment. These antibodies are thought to coat the mucosal surfaces lining the gut and prevent invasion by ineffective organisms.
Milk also contains cells of several types which are important for immune responses, including lymphocytes capable of reacting directly with antigens to which the cow has been sensitized (Smith and Schultz 1977).
Other non-specific agents are also present, which inhibit the multiplication of micro-organisms. Although many of these factors remain in fresh skim milk, drying -especially at high temperatures- destroys them. So even feeds containing a large proportion of dried skim milk lack important components.
Preston (1973) summarizes extensive trials involving many thousands of calves which received milk plus supplementary food, including concentrates. The mortality of single-suckled calves was 5.2%; the mortality of those fed with milk from buckets was 12.3%. Intestinal parasites were more common in the bucket-fed animals (though not as common as in multiple-suckled calves (Ugarte and Preston 1972)).
Although the temperature of bucket-fed milk, the rate of drinking and the quantity at each feed can also affect the health of bucket- fed calves (Stewart 1976; Taylor and Stewart 1976), these results suggest that the risk of infection is definitely increased by simply handling the milk. Possibly the milk antibodies and cells attach to the surface of the bucket, so less are available to coat the gut mucosa. The hygiene on the Cuban farms, where these trials took place, may have been less than ideal but that would apply to most farms in developing countries.
Moreover, when Everitt and Evans (1970) analysed the records of 2673 calf deaths on experimental farms in New Zealand, they found that 7.8% of those fed by bucket died, compared to 0.9% of those suckled (ruminal and abomasal bloat, which accounted for 10% of the deaths, occurred only in bucket-fed calves).
Presumably non-fatal as well as fatal infections also develop less frequently in suckled calves. Growth rate as well as mortality data from more recent trials, with various breeds of cows in several countries, indicate that restricted suckling is preferable to bucket-feeding (Preston 1983). This confirms earlier results (Everitt et al 1968; Everitt and Phillips 1971; Smith et al 1973; Paredes et al 1981) which showed that the growth rate of suckled calves tends to be better than that of calves fed by bucket.
Since, where feed is adequate, the live-weight gain of beef calves between 3 months and slaughter is closely correlated with that from birth to 3 months (Everitt et al 1969), conditions promoting early rapid growth may have substantial long-term advantages.
Effect on the cow
In some trials in which suckling enhanced milk production certain other effects on the cows were observed:
i) Suckling may prolong lactation (Everitt et al 1968; Everitt and Phillips 1971; Chandler and Robinson 1974), although some results do not confirm this (Thomas et al 1981).
ii) Suckling may prolong anoestrus, the delay being related to the duration of suckling (Everitt et al 1968; Thomas et al 1981). Moller (1970) reported that the growth of ovarian follicles in sucked cows are slower than in machine-milked ones, so that the first ovulation occurred significantly later. Moreover, the proportion of animals showing signs of oestrus was also reduced. Suckling twice a day has a less marked effect than continuous suckling, which could explain why some other workers observed no prolongation of anoestrus (Veitia and Simon 1972; Ugarte and Preston 1972; Fulkerson et al 1978). It should also be noted that Preston (1983) concludes that although distinctive signs of oestrus in cows suckled twice daily may be lacking - making successful AI programmes difficult - these so-called `silent heats' can often be detected by the bull, and natural mating generally results in no delay to the next calving.
iii) In many of the trials cows that suckled calves were reported to suffer less from mastitis than milked ones (Everitt et al 1968; Veitia and Simon 1972; Preston 1973; Walsh 1974). Others observed no difference, possibly because the overall incidence of mastitis was low (Fulkerson et al 1978; Thomas et al 1981). Preston (1983) concludes from more recent data that there is indeed a beneficial effect on udder infection from twice-daily suckling.
iv) In the case of breeds which do not normally let down milk in the absence of the calf (eg: Bos indicus breeds and their crosses), it is traditional practice (Preston T R, personal communication) to stimulate milk flow by very brief suckling followed by partial (eg: three teats only) milking, after which the calf is allowed to suck the residual milk.
The data discussed here indicate that the practice of feeding calves on milk substitutes from an early age is likely to be economically inappropriate for many resource-poor farmers in a developing country, especially if a healthy calf is regarded as a significant asset. Moreover, since the well-fed cow can respond to the stimulus of suckling after milking by secreting more milk, early weaning may in fact fail to increase the amount available for sale. Longer lactations and a reduced risk of mastitis are additional benefits which may result from restricted suckling and the reproductive pattern of the cow is likely to be little affected, provided natural mating is used.
Of special importance in tropical countries is the fact that many Bos indicus breeds and even their F1 crosses with European breeds will not let down their milk unless stimulated by being permitted to suckle their calves briefly prior to hand or machine milking.
Nevertheless, further trials are needed with specific breeds of cattle and within the constraints of specific patterns of farming.
The following particular questions need attention in each situation:
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