| Livestock Research for Rural Development 11 (2) 1999 | Citation of this paper |
An experiment was carried out to evaluate the effect of three periods of restricted suckling on milk yield and other productive variables of Bos indicus x Bos taurus cows and on the performance of their calves. Thirty six Brahman x Holstein cows were assigned using a completely randomized design to three weaning age treatments: at 8, 16 and 24 weeks. The calves were suckled by their dams for 30 minutes after the morning milking and received 1 to 2 kg/day concentrate, cut forage ad libitum and grazed on paddocks of Cynodon dactylon for 7 h daily. The cows were milked twice a day, received 2 kg/day of concentrate per milking and grazed on pastures of Cynodon dactylon and Digitaria swazilandensis. Total milk was 2249 kg/lactation without differences between treatments (P>0.05). Daily milk yield decreased by 23 % on average during the week following weaning, but the trend of the lactation curve was recovered after 2 to 4 weeks. Decreasing the suckling period from 24 to 8 weeks increased saleable milk from 1694 to 2175 kg/lactation (P<0.05) and decreased suckled milk from 430 to 179 kg (P<0.01). The liveweight gain of the calves was not affected.
These results show that by decreasing weaning age to 8 weeks, the advantages of restricted suckling are maintained but but the quantity of saleable milk is increased. The growth rate of the calves is not affected as they eat more concentrates to compensate for the reduction in suckled milk. For every 1 kg of additional concentrate used, 5 kg of additional milk is available for sale, with positive economic returns in most price conditions.
Restricted suckling is a common practice for rearing calves in dual-purpose systems, and is extensively used in lowland Latin America. It has several advantages over artificial rearing, such as higher milk yield and lower mastitis incidence in cows and higher liveweight gains in calves (Sandoval et al 1995; Sahn et al 1997). But about 42 % of total milk with a higher content of fat than saleable milk is consumed by the calves (Sandoval et al 1995). Many variants are possible, but the most frequent method is to suckle the calf during the entire lactation. An option to maintain the advantages of suckling and decrease the amount of milk consumed by the calves is to reduce the period of suckling. However, in Holstein cows this has reduced cows' milk yield (Bar-Paled et al 1995) and the liveweight gain of the calves after weaning (Ugarte 1976).
The following experiment was carried out to evaluate the effect of three suckling periods on milk yield and other productive variables of Bos indicus x Bos taurus cows and on the performance of their calves.
The experiment was carried out at the Faculty of Agronomy, of the Central University of Venezuela, located in Maracay at 450 m above sea level. Annual rainfall is 989 mm concentrated mainly in the period from May to October. Relative humidity is 74 % on average and mean maximum and minimum temperatures are 31.8 and 18.9 ºC.
A completely randomized design was used to compare three treatments, W8, W16 and W24, consisting of three weaning ages: 8, 16 and 24 weeks. Thirty-six Brahman x Holstein cows were used, with ½ to ¾ European genes and a parity of two or more. The cows started calving in May and were assigned in sequence to each treatment. After calving, the cows remained with their calves for three days in individual roofed pens and thereafter returned to the milking herd, grazing 18 paddocks of Cynodon dactylon and Digitaria swazilandensis with a total surface of 20 ha. At 0600 and 1600 h the cows were milked by machine and supplemented at each milking with 2 kg of a concentrate with 19.0 % crude protein (Table 1). After the morning milking the cows were joined with their calves during 30 minutes for suckling. One bull was always with the cows in the field.
| Table 1: Ingredients (%) of cow and calf supplements | ||
Calf supplement |
Cow supplement |
|
| Wheat middlings | 35.0 |
35.0 |
| Maize meal | 44.6 |
12.0 |
| Fish meal | 7.0 |
7.0 |
| Sugar cane Molasses | 10.0 |
10.0 |
| Mineral mixture | 2.4 |
1.0 |
| Common salt | 1.0 |
1.0 |
| Urea | 1.0 |
|
| Poultry litter | 33.0 |
|
The calves were housed in roofed pens in groups of four according to treatment. Fresh Pennisetum purpureum (8.7 % crude protein in dry matter) and water were always available. From 0800 to 1500 h the calves grazed in four paddocks of Cynodon dactylon (7.9 % crude protein) with a total area of 0.25 ha. A concentrate with 17.5 % crude protein was offered after the first week at a level of 1 kg/day until weaning (Table 1). After weaning, the calves received 2 kg/day of concentrate, except those in treatment W8 which received 1.5 kg/day between weeks 8 and 16 and 2 kg/day after week 16.
Saleable milk was measured daily during the whole lactation. Milk consumed by the calves was estimated twice a week by weighing the calves before and after suckling. The cows were weighed every two months, oestrus was detected by visual observation and conception determined by rectal palpation, 60 days after oestrus detection. The weight of the calves before suckling and weekly weights after weaning were used to calculate liveweight gain (by regression of liveweight on time) over 8 week periods during the 34 weeks of measurements. Cases of diarrhoea in the calves before weaning were recorded.
The length of the suckling period did not affect total milk yield during the lactation (Table 2). There was an average reduction of 23 % in milk yield during the week following weaning in all treatments, but after a period of 4 weeks in W8 and 2 weeks in W16 and W24, it increased again and continued the trend of the lactation curve (Figure 1). This effect was also observed by Bar-Peled et al (1995) after weaning Holstein calves at 6 weeks of age who suggested that it was more related to poor milk removal, due to psychological disturbance of milk ejection, than to a direct inhibition of milk secretion per se. The absence of differences in total milk yield (Table 2) between the treatments indicates that a short period of 8 weeks is sufficient to induce the benefits in milk production of restricted suckling over artificial rearing as has been pointed out by several researchers (see Sandoval et al 1995)
Figure 1: Milk yield of cows that suckled their calves for 8, 16 or 24 weeks
Milk consumed by the calves increased with the length of the suckling period from 7.6 % of total milk in W8 to 20.2 % in W24. The latter value was lower than the 42 % average reduction reported by Sandoval et al (1995) in their review. However, it should be noted that, in our experiment, suckling was restricted to the early part of the lactation and to only one of the two daily milkings. The amounts of milk sucked by the calves decreased steadily with advance in lactation at a higher rate than total milk yield. In treatment W24 it declined from 37.4 % of total milk during the first 8 week period to 23.5 % during the third 8 week period (Table 2). Saleable milk increased after weaning in all treatments (Table 2), in spite of the fall in total milk mentioned earlier, and was inversely related with the suckling period.
Table 2: Milk production (total, suckled and saleable) during different periods of lactation for suckling periods 8 (W8), 16 (W16) and 24 (W24) weeks |
||||
| W8 | W16 | W24 | SEmean | |
Full lactation (kg) |
||||
Total |
|
|
|
|
Saleable |
|
|
|
|
Suckled |
|
|
|
|
Length in days |
|
|
|
|
Saleable per period (kg/day) |
||||
Weeks 1-8 |
|
|
|
|
9-16 |
|
|
|
|
17-24 |
|
|
|
|
25-34 |
|
|
|
|
Suckled per period (kg/day) |
||||
Weeks: 1-8 |
|
|
|
|
9-16 |
- |
|
|
|
17-24 |
- | - |
|
|
| *P<0.05, **P<0.01 | ||||
Weaning age had no apparent effect on reproductive variables (Table 3). Conception rate at 120 days was higher and interval from calving to conception (ICC) was shorter in W8 than in W16, but there were no differences between early weaning (W8) and late weaning (W24).
Table 3: Conception at 120 days and interval calving to conception (ICC) |
||||
| W8 | W16 | W24 | SEmean | |
Conception at 120 days (%) |
83.3a |
33.3b |
58.3ab |
20.4* |
Interval: calving to conception (days) |
86.9a |
139b |
106ab |
56.2* |
| *P<0.05 | ||||
There is contrasting evidence in the literature for the effect of suckling versus artificial rearing on interval from calving to first oestrus, with no effect (Ugarte and Preston 1975; Alvarez et al 1980; Sanh et al 1997) or a short delay in cows that suckled their calves (Little et al 1971; Mejía et al 1998). The conception delay in treatment W16 of this study was associated with a greater loss in liveweight after calving and a longer period to recover the lost weight, which cannot be explained with the information available (Figure 2).
Figure 2: liveweights of cows that suckled their calves for 8, 16 or 24 weeks
The liveweight gain of the calves was not influenced by weaning age (Figure 3).
Figure 3: Growth curves of calves weaned atg 8, 16 or 24 weeks
The liveweight gain immediately after weaning was similar to that before weaning (Table 4). These results contrast with those of Ugarte (1976) who observed a lower liveweight gain after weaning in calves weaned at an older age. These differences could be associated with concentrate consumption prior to weaning. In Ugarte's experiment, average concentrate consumption during the first 8 weeks was 0.26 kg/day compared with 0.48 kg/day observed in this study. For some reason these calves were used to consuming a larger amount of concentrate before weaning and were less affected by the change in diet after weaning. No deaths were observed during the experiment and the incidence of diarrhoea was low, with 1, 6 and 4 animals in treatments W8, W16 and W24. There was an indication that incidence of diarrhoea was lower in calves weaned early and therefore consuming milk for a short period.
Table 4: liveweight gain and concentrate intake of calves |
||||
| W8 | W16 | W24 | SEmean | |
Concentrate intake (kg/day) |
||||
Weeks: 1-8 |
0.45 |
0.53 |
0.48 |
|
Weeks 9-16 |
1.38 |
0.92 |
0.89 |
|
Weeks 17-24 |
2.00 |
1.75 |
0.94 |
|
Concentrate intake (kg) |
||||
Weeks: 1-34 |
355 |
319 |
261 |
|
liveweight gain (kg/day) |
||||
Weeks: 1-8 |
0.49 |
0.41 |
0.53 |
0.135 |
Weeks 9-16 |
0.59 |
0.59 |
0.64 |
0.137 |
Weeks 17-24 |
0.70 |
0.69 |
0.73 |
0.135 |
Weeks 25-34 |
0.58 |
0.57 |
0.60 |
0.138 |
Weeks 1-34 |
0.62 |
0.60 |
0.66 |
0.092 |
These results have important practical implications from the point of view of farm income. Early weaning increased the amount of saleable milk from 1694 to 2175 kg between treatments W24 and W8 (Table 2) and required higher inputs of concentrate for the calves to maintain their growth rate (355 vs. 261 kg in W24 and W8, Table 4). However, the cows in group W8 had on average 481 kg more saleable milk than the cows in group W24, while the calves ate 94 kg more concentrates. This means that for every 1 kg of additional concentrate used the saleable milk increased 5 kg on average.The substitution of milk by concentrate has economic advantages in most price conditions. This system allows the benefits of restricted suckling to be obtained while at the same time maintaining a high proportion of saleable milk.
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Bar-Peled U, Maltz E, Bruckental I, Folman Y, Kali Y, Gacitua H, Lehrer A R, Knight C H, Robinzon, B, Voet H and Tagari H 1995 Relationship between frequent milking or suckling in early lactation and milk production of high producing dairy cows. Journal of Dairy Science 78:2726-2736
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Mejía C E, Preston T R and Fajersson P 1998 Effects of restricted suckling versus artificial rearing on milk production, calf performance and reproductive efficiency of dual purpose Mpwapwa cattle in a semi-arid climate. Livestock Research for Rural Development. Volume 10, Number 1: http://www.cipav.org.co/lrrd/lrrd10/1/mejia101.htm
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Sanh M V, Preston T R and Fajersson P 1997 Effects of restricted suckling versus artificial rearing on performance and fertility of Bos taurus and Bos indicus cows and calves in Tanzania. Livestock Research for Rural Development. Volume 6, Number 6: http://www.cipav.org.co/lrrd/lrrd6/3/10.htm
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