RESTRICTED SUCKLING IN DUAL PURPOSE SYSTEMS

by

J. Ugarte

INTRODUCTION

In the majority of the countries with a high level of agricultural development, the feeding of dairy calves is based on artificial rearing. The availability of milk substitutes based on by-products from the dairy industry has stimulated artificial rearing. This is not so in developing countries where there is a lack of fresh milk. In this case, artificial rearing must be based on fresh milk. Thus it is not logical to milk by hand or machine and later give part of the milk to the calf. It is better to make use of the calf's ability to extract milk from the cow.

Traditional rearing of dairy calves is characterized by the presence of the calf with the cow during milking to stimulate milk let-down and it stays with her after milking to consume the milk remaining in the udder. The time the cow is with the calf varies between 1 and 12 hours and is inversely related to the age of the calf. Age at weaning is rarely less than 6 months.

However, in dual purpose herds, natural (traditional) rearing does not efficient use of the cows' potential for the production of milk for the market. Hence, a variant of natural rearing was developed, called restricted suckling, characterized by the reduction in the time the calf remains with the cow each day, which is that strictly necessary for suckling, and in the age at weaning onto other feeds. This allows a greater economic effectiveness since:

1. it uses the maximum milk potential of the cows through the consumption by the calf of the residual milk.
2. it achieves high milk yields at milking and good calf growth.
3. it attains satisfactory reproductive performance and a low incidence of mastitis
4. it maintains a low calf mortality rate.

RESULTS OF RESTRICTED SUCKLING

Residual milk

15% of the milk in the udder at the start of milking remains at the end as residual milk, containing 3 times more fat content than normal milk (Lane et al., 1970).

The amount of residual milk has been correlated to total milk and with the interval between milkings. It varies throughout the lactation from 9.1 and 23.5% of total production in the first and tenth months of lactation respectively (Marx, 1971). Only small amounts of residual milk have been found in the udder of cows after the calves have suckled (1.2 – 3.4%), always less than in hand or machine milked cows (Kreilis et al., 1971).

Considering that the rate of milk secretion is more intense immediately after milking and that the amount of residual milk remains relatively constant, it is expected that, by delaying the suckling time, this recently secreted milk would also be consumed by the calf, with a possible reduction in the amount of milk to be obtained in the following milking. Milk consumption rose from 3.8 to 5.2 litres on increasing this interval from 20 min to 2 hours while production obtained at milking was reduced from 13.9 to 12.4 litres for a total production of 17.6 litres. By this method, the producer may obtain a certain amount of milk for the calf without affecting the total production of the cow.

The frequency of sucklings also affects the destination of milk produced. Thus, comparing suckling once or twice a day, Ugarte and Preston (1972) found that milk consumption did not differ between maternal breeds but was 50% greater for twice a day, while total production (milking and calf consumption) remained equal (Table 1). In the experimental cows, the decrease in milk production during the milking of Holstein cows suckling calves twice and once a day was 3.5 and 0.4 litres respectively, while in the F1 (Holstein x Zebu) it was of 3.6 and 1.2 litres. Suckling once or twice are equally effective methods of taking the maximum advantage of milk production in cows of this potential.

A satisfactory variant was the combination of different numbers of sucklings (Ugarte and Preston, 1973) (Table 2). On reducing it from two to one from the fourth week of age to weaning (10 weeks), milk consumption was reduced by 54% (3 litres per day), as was the daily gain of the calf, although this was acceptable (478 g/day) and resulted in an average of 535 grams over the whole period 7 – 70 days. The production obtained at milking increased by 4.2 litres (31%), while the cumulative total to weaning was similar to the control (without calves) and total production was 28% higher.

It should be noted that the intervals between milkings were 15 and 9 hours and that restricted suckling took place after the milking with the shortest interval (afternoon), when the cows produced less milk. To increase consumption by the calf, suckling should take place in the morning, since differences of 0.8 and 1.0 litres were found on suckling the calves in the morning, compared to the afternoon, with intervals between milkings of 15:9 and 16:8 hours (Table 3).

Age at weaning

This has usually ranged between 4 and 8 weeks. However, in systems of natural rearing, weaning ages have generally been high since it is not common practice to use sufficient amounts of concentrates. The calf must receive milk in the early stages to avoid seriously reducing performance.

When calves suckling once a day were weaned at 35, 56 and 70 days, no significant differences were observed in weight at weaning and at 154 days (Ugarte, 1977) (Table 4). On the other hand, total milk consumption increased with age at weaning. Total production (milking + consumption) over the period 7–70 days was apparently not affected by age at weaning. As particularly careful management is needed when calves are weaned at 35 days, 56 day weaning is recommended.

Milk production throughout lactation

A study carried out by Ugarte and Preston (1975) with 60 cows and calves suckling twice a day and an equal number without calves showed that from weaning (70 days) until cows were dried off, milk production did not differ significantly between treatments (6.1 and 5.7 litres per day, respectively). Lactation length did not differ either and total daily production throughout the lactation of cows suckling calves (milking + consumption) was 8.28 litres, while in cows without calves it was 7.35 litres (Table 5).

These results agree with those obtained at a commercial level (with 97,678 cows milked twice a day for one year (Ugarte, 1977)). Daily milk production during milking was higher without the calf but, since about 332 litres were consumed by the calf, the F1 and F2 cows in restricted suckling produced 1.3% and 9% more milk in total (Table 6).

Mastitis

A study of 61 herds in tropical areas revealed that the incidence of mastitis represents 12.6% of milking cows (Fustes et al., 1985). A lower incidence of clinical and subclinical mastitis was found during the suckling period. After weaning, no significant differences were found between rearing systems (Ugarte and Preston, 1975) (Table 7). This is due to several factors, such as the mechanical effect of suckling, the cleaning effect of the saliva and a more complete emptying of the udder.

Table 7 (continued).

Reproduction

It is accepted that natural rearing produces long calving intervals and this has been more evident on increasing the age at weaning. However, when the animals are early weaned (70 days) these considerations are not valid.

This was confirmed in a population of F1 and F2 (Holstein x Zebu) cows, without calves or suckling calves until 90 days (Table 8). Intervals between calving and conception were slightly longer with restricted suckling compared to artificial rearing, but considerably less than with traditional rearing. In another study, Rodriguez (1987), on analyzing more than 120,000 cows, reported intervals of 109, 151 and 218 days to first insemination and 128, 166 and 240 days to conception for artificial rearing restricted suckling and traditional rearing systems respectively.

¹ Mainly zebu x Brown Swiss in different proportions

( ) Number of cows on each system

^a Weaning at 3 – 4 months of age

^b Weaning at 6–8 months of age

Mortality

On analyzing deaths occurring in 195,000 births during a one year period, values found were of 9.9%, 6.5% and 7.2% mortality for calves reared artificially, by restricted suckling and by natural rearing (Table 9).

Cost of rearing

The cost of a calf reared artificially was 115.59 Cuban pesos, while, with restricted suckling, it was of 82.89 Cuban pesos, giving a difference of 32.70 Cuban pesos (Ugarte, 1977). Rodriguez (1987) also found a favourable difference for calves reared by suckling of 55.24 Cuban pesos (142.15 and 86.94 Cuban pesos in artificial rearing and suckling respectively).

REFERENCES

Fustes, E., Avila, C. and Ortega, L. 1985 Efectos de la mastitis bovina sobre la producción lechera y la economia agropecuaria. Rev. Salud Animal 7: 91–98.

Kreilis, M.L., Silinish, A.A. and Maksimova, E.P. 1971 The completeness of emptying of the udder with various methods of milk removed. Anim. Breed. Abstr. 39: 666.

Lane, G.T., Dill, C.W., Armstrong, B.C. and Switzer, L.A. 1970 Influence of repeated oxytocin injections on composition of dairy cows milk. J. Dairy Sci. 53: 427–433.

Marx, G.D. 1971 Use of a quarter milking machine to study factors involved in mastitis. Paper 7549. Scientific J. Serv. Minn. Agric. Exp. Stat.

Rodriguez, E. 1987 Incidencia de los sistemas de crianza de terneros en la actividad productiva y reproductiva en el ganado. Reunión ACPA. MIN. AGRIC. La Habana.

Ugarte, J. 1977 Crianza de terneros lecheros en amamantamiento restringido. Tesis Cand. Dr. Cs. ISCAH, La Habana.

Ugarte, J. and Preston, T.R. 1972 Rearing dairy calves by restricted sucking. 1. Effect of suckling once or twice daily on milk production and calf growth. Rev. cubana Cienc. agric. (Eng. ed.) 6: 173–182.

Ugarte, J. and Preston, T.R. 1973 Rearing dairy calves by restricted suckling. 3. The effect of reducing suckling frequency to once daily, after the fourth week on milk yield and the the growth of the calf. Rev. cubana Cienc. agric. (Eng. ed.) 7: 147–154.

Ugarte, J. and Preston, T.R. 1975 Rearing dairy calves by restricted suckling. 6. Effects on milk production, reproductive performance and incidence of clinical mastitis throughout the lactation. Rev. cubana Cienc. agric. (Eng. ed.) 9: 15–26.