X. Jingtao,1 Y. Rongzhen1 and Sh. Shengzhong2
1. Qinghai Academy of Animal and Veterinary Sciences, Xining 810003, Qinghai, P.R. China
2. Datong Draft Animal Reproduction Farm, Datong 810102, Qinghai, P.R. China
Thirty mother–daughter and 30 mother–son pairs were arranged into three groups of not-milking, once milking per day and twice milking per day (10 mother–daughter and 10 mother–son pairs for each group) to study the effect of milking methods on the growth and development of calves from birth to 18 months of age. The results showed that the mean live weights of the calves under these three respective groups were 99.0, 76.6 and 58.0 kg at 6 months, 97.6, 78.9 and 64.6 kg at 12 months, and 146.5, 131.9 and 91.0 kg at 18 months of age. The effects of milking methods on live weights of calves were significant. The results strongly suggest that, for a better development of calves and their subsequent production and reproduction, nursing cows should not be milked or, if milked, only once a day.
Keywords: Calf, cow, growth, milking, yak
It is well known that the early growth and development of yak calf will affect its production and reproduction later in life. Commonly, local herdsmen milk cows twice, or even three times per day during the peak milking period in most of the yak raising areas. It is unlikely that the yak calf being nursed by such a cow can obtain enough nutrients to meet its early growth and development. This has implications for the productivity of the overall herd. This study was designed to explore the potential growth and development of yak calves under different rearing methods.
The study was conducted in Datong Draft Animal Reproduction Farm from 1996–1997. The farm is located in the south of Daban Mountain with altitude of 3000–3900 metres above sea level (masl). The mean annual temperature was 0.5–1°C, the lowest temperature –28°C, and mean annual rain fall 570–610 mm. There were 5200 km2 grassland, with which 1700 yak and 2000 sheep were maintained. Thirty mother–daughter and 30 mother–son pairs were arranged into three groups of: 1) not-milking, 2) once milking per day, and 3) twice milking per day. Each group had 10 mother–daughter and 10 mother–son pairs. All animals were grazed on natural grassland without any supplementary feeding.
All experimental yak calves were ear-tagged and weighed at birth, 6 months, 12 months and 18 months of age. Body measurements, including body height, body length, heart girth and cannon bone circumference were taken at each age of measurement. Milking was stopped for all cows on 10th October and calves were weaned the next February.
Based on the data shown in Tables 1 and 2, it is clear that the growth and development only occurred during the two warm seasons in the intervening period between birth and 6 months of age and from 12 to 18 months of age. Mean relative weight increased by 685.7 and 50.1%, respectively, for calves of the non-milked cows during the two warm seasons. Corresponding figures for calves whose dams were milked once were 527.9 and 67.6% while those for last group (milked twice) were 344.3 and 41.0%, respectively. Weight gain of yak calves was most rapid between birth and 6 months of age. During the cold season coinciding with growth from 6 to 12 months of age, the relative live weight gains were only –1.41, 3.0 and 11.2% for the three respective experimental groups.
Table 1. Live weight (kg) of calves under different milking regimes.
Group |
Sex |
No. |
Birth |
6 months |
Weight |
12 months |
Weight gain |
18 months |
Weight gain |
1 |
♂ ♀ Average |
10 10 20 |
13.3 ± 1.8 12.2 ± 2.2 12.6 ± 2.1 |
107.8 ± 13.9 90.2 ± 7.79 9.0 ± 14.2 |
94.5 78.2 86.4 |
105.1 ± 11.4 90.1 ± 5.2 97.6 ± 11.6 |
–2.7 –0.1 –1.4 |
152.2 ± 10.3 140.8 ± 4.2 146.5 ± 9.6 |
47.1 50.7 48.9 |
2 |
♂ ♀ Average |
10 10 20 |
12.4 ± 2.2 12.1 ± 1.51 2.2 ± 1.8 |
78.6 ± 7.7 74.5 ± 10.0 76.6 ± 8.9 |
66.2 62.4 64.4 |
80.6 ± 5.5 77.2 ± 7.1 78.9 ± 6.4 |
2.0 2.7 2.3 |
137.2 ± 7.5 126.5± 6.2 131.9 ± 8.7 |
56.6 49.3 53.3 |
3 |
♂ ♀ Average |
10 10 20 |
12.9 ± 1.8 13.2 ± 2.0 13.0 ± 1.9 |
58.8 ± 8.5 57.4 ± 9.8 58.1 ± 9.0 |
45.9 44.2 45.1 |
65.8 ± 8.2 63.4 ± 8.6 64.6 ± 8.3 |
7.0 6.0 6.5 |
94.4 ± 5.9 87.8 ± 4.3 91.1 ± 6.0 |
28.6 24.4 26.5 |
All pair-wise differences in live weight between the three groups of yak calves were significant (P<0.01) at all ages, that is, at 6, 12 and 18 months of age. This indicates that the different milking methods had substantial influence on the early growth and development of yak calves.
Because of the limitations of the natural environment, production situation and feed condition in the area, the early growth of yak mainly rely on the cow's milk. The daily weight gains of 6 months old calves were 489 g, 357.8 g and 250.6 g, respectively, for the three groups in this study. These figures illustrate the extent to which reduced milk available to the young calf does affect its growth.
Although the calves from the group of cows milked twice per day had a compensatory growth during the next warm season, the rate of growth was still much less than it was for the calves in the other two groups.
Table 2. Body measurements (cm) of calves under different milking regimes.
Group |
no. |
Body measurement |
At birth |
Six months |
Net gain |
12 months |
Net gain |
18 months |
Net gain |
1 |
20 |
Height |
53.6 ± 5.5 |
92.0 ± 4.8 |
38.4 |
93.3 ± 4.2 |
1.3 |
9.6 ± 2.8 |
6.3 |
Length |
49.9 ± 3.8 |
96.7 ± 5.7 |
46.8 |
98.3 ± 4.9 |
1.7 |
104.1 ± 5.1 |
5.8 | ||
Hear girth |
57.7 ± 7.0 |
123.9 ± 7.7 |
66.2 |
125.8 ± 4.7 |
2.0 |
137.6 ± 4.3 |
11.8 | ||
Cannon bone circumference |
8.7 ± 0.9 |
13.4 ± 1.4 |
4.7 |
15.0 ± 1.4 |
1.6 |
17.8 ± 1.0 |
2.8 | ||
2 |
20 |
Height |
50.6 ± 5.7 |
88.0 ± 3.7 |
37.4 |
89.4 ± 3.2 |
1.4 |
91.5 ± 2.4 |
2.1 |
Length |
48.7 ± 5.6 |
88.5 ± 4.0 |
39.9 |
91.6 ± 5.5 |
3.1 |
102.3 ± 3.5 |
10.7 | ||
Hear girth |
53.2 ± 4.7 |
108.8 ± 6.5 |
55.6 |
111.4 ± 4.5 |
2.6 |
122.2 ± 5.8 |
10.8 | ||
Cannon bone circumference |
8.5 ± 0.5 |
13.6 ± 1.1 |
5.1 |
14.2 ± 1.0 |
0.6 |
18.8 ± 1.1 |
4.7 | ||
3 |
20 |
Height |
53.7 ± 3.4 |
81.1 ± 3.4 |
27.4 |
82.0 ± 3.2 |
0.9 |
90.6 ± 1.4 |
8.6 |
Length |
48.6 ± 3.7 |
83.4 ± 4.3 |
34.9 |
85.7 ± 1.8 |
2.3 |
94.7 ± 1.5 |
9.0 | ||
Hear girth |
54.3 ± 5.5 |
101.1 ± 6.0 |
46.9 |
101.1 ± 4.50 |
0 |
116.2 ± 3.9 |
15.1 | ||
Cannon bone circumference |
8.6 ± 0.6 |
12.0 ± 1 .1 |
3.4 |
12.6 ± 1.0 |
0.6 |
15.1 ± 0.8 |
2.5 |
We suggest that cows should not be milked if they have twin calves, are nursing their first calves, or are in their later stages of production (that is, advanced parities). Definitely, for veal production, which requires raising calves on milk and slaughtering by weaning, milking should not be practised at all. We also recommend that cows nursing calves which have been selected as replacement heifers or bulls should not be milked. To meet the milk demand by the local herdsmen, the method of milking once per day may be adopted in the normal management. However, the twice milking per day should strictly be forbidden to improve the quality and production of the herds.
Calves should be weaned at 6 months of age if their dams are not milked or only milked once per day to renew the cows' body condition so that they can be in oestrus and be mated the next breeding year. This is the only way to increase reproductive performance in the yak herds.
The authors are grateful to Mr Lei Huanzhang and Mr Lou Xiaolin for their instruction and help in this work.
