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Growth


As would be expected, growth and development of the yak is highly influenced by the seasons, which, along with the location, largely determine pasture growth and hence the feed supply. Age, sex, type or breed of yak and herd management are among the other main causes of variation.

Body weight

Birth weight

In general, birth weight is low, ranging from 10 kg to 16 kg and representing about 3 to 7 percent of adult weight. The relatively low birth weight is a consequence of a relatively short gestation length (see Chapter 5) and the fact that in mid- and late pregnancy the yak, typically, has to exist on ground that is frozen and covered with ice and snow. Also, the yak does not normally have the benefit of supplementary feeding. For these nutritional reasons, the physical condition of the female yak is at its lowest in late pregnancy thus leading to nutrient deficiency for the foetus at the very time when the foetus is at its most demanding. The consequence is relatively poor foetal development. Table 6.1 provides some results from different sources and breeds - showing the Jiulong yak of Sichuan province with the highest absolute birth weights and the "Pengbo" yak in Tibet with the lowest.

Table 6.1 Birth weights of male and female yak of different breeds at different locations in China.

Province

Breed or local yak*

Male

Female

Source (first author et al.)

No.

Weight (kg)

Proportion of adult weight (%)***

No.

Weight (kg)

Proportion of adult weight (%)***

Sichuan

Jiulong

27

15.9

2.9

24

15.5

5.8

Cai Li et al., 1980a

Sichuan

Maiwa

77

13.4

3.2

71

11.9

6.5

Chen Xiafei et al., 1981

Sichuan

Maiwa

35

14.7

3.6

60

13.0

5.8

Longri Breeding Farm, 1993

Yunnan

Zhongdian

11

14.5


14

12.8


Duan Zhongxuan and Huang Fengying, 1982

Gansu

Tianzhu White

25

12.7


24

10.9


Research Co-operative Group, 1980 - 1987

Gansu

Maqu#

45

14.6


46

13.5


Zhao Bingyao et al., 1984

Qinghai

Plateau

11

13.4


11

13.1


Lei Huanzhang et al., 1983

Qinghai

Datong#

52

13.2


59

11.8


NW China Animal Science Institute, 1960

Qinghai

Plateau (?)

37

13.2

3.1

37

11.8

3.5

Song Jianxin et al., 1982

Qinghai

Guoluo

16

11.7


24

11.8


Li Quan et al., 2000a

Tibet

Alpine

46

13.7


32

12.8


Research Co-operative Group 1980 - 1987

Tibet

Pengbo#**

(63)

(10.5)





Ma Zongxiang and Dou Yaozong, 1981

Xinjiang

Bazhou

8

15.8


17

14.3


Agri. Exploit. Acad. Of Xinjiang, 1984

* Jiulong, Maiwa, Tianzhu White and Alpine are "listed" Chinese yak breeds. ** Number and average of male and female yak calves combined. *** Birth weight as a proportion of adult weight. # Yak name denotes locality or farm ? breed or type assumed.

Although breed differences in birth weight may exist, it is not possible, as already mentioned, to differentiate between the effects of breed and those of location. Female calves are, on average, about 1 kg lighter at birth than the males.

Supplementary feeding of dam over winter. An experiment conducted at the Longri Breeding Farm examined the effect of two methods of supplementary feeding of the dams during pregnancy. (This experiment, conducted by the then Southwest Nationalities College [now University] with support from UNDP/FAO was described in Chapter 5 in the section on calf survival). Table 6.2 shows the effects of supplementary feeding of dams in winter or early spring on birth weight and the subsequent daily gain of the calves.

As seen in Table 6.2 the effects of supplementary feeding of the dams were small but positive both on birth weight and daily weight gain and may have reached statistical significance, according to the report of Wen Yongli et al. (1993). A feeding experiment conducted by Dong Shikui et al. (personal communication, 2000) on Tianzhu White yak showed that the birth weight was improved by nearly a third and weight gain of calves was doubled when the dams were supplemented with urea multinutritional molasses blocks (UMMB) from the start of December 1998 to the end of April 1999. In both experiments, the improved weight gain was likely to be attributable to the advantages of a higher birth weight and a slightly better milk yield of the supplemented dams (see also Tables 6.6 and 6.7 for the effects of rearing on calf growth). Any advantage in terms of body weight must also be viewed in conjunction with the small but positive effect of the winter feed supplementation on the number of calves born and reared (see Table 5.10). Further information on the effects of supplementary feeding is presented in Chapter 14.

Table 6.2 Birth weights and weight gain to 90 days of age of Maiwa yak calves from three groups of dams Least squares means and standard deviations [Source: Wen Yongli et al. 1993]

Year

Treatment group

No. calves

Birth weight (kg)

No. calves

Daily weight gain (g/day) (90 days)

Mean

SD

Mean

SD

1989/90

Hay

36

16.2

2.2

32

300

83

Paddock grass

41

16.0

2.2

36

298

54

Control

81

14.5

2.5

66

279

51

1990/91

Hay

35

18.1

2.4

30

316

88

Control

98

15.6

3.7

98

295

57

a) fed hay from mid-December to end of April, b) allowed access to conserved grass paddocks from 1 April for 45 days and c) unsupplemented, control.

Parity and age of cow. Both parity and age of yak dam have effects on the birth weight of their calves, as shown in Table 6.3 and as widely reported in studies on ordinary cattle elsewhere. Data are again taken from the Longri experiment involving trials of the effects of supplementary feeding during pregnancy. (Because supplementary feeding of the dams has affected calf weights in this experiment, the overall mean birth weight of all the calves is also somewhat higher than it would be without the inclusion of the feed-supplemented groups [the least squares mean for each treatment group were shown in Table 6.2]. Therefore, effects of parity and age of dam, shown in Table 6.3, are presented as deviations from the overall fitted mean of the data.)

Table 6.3 Effects of parity and of age of yak cow on the birth weight of her calf, shown as deviations from the least squares fitted mean [Source: Chen Zhihua et al., 1994]

Parity of dam

No. of cows

Deviation of birth weight (kg)

Age of dam (years)

No. of cows

Deviation of birth weight (kg)

1

37

-0.02

4

33

-0.52

2

27

-0.34

5

9

-0.24

3

26

-0.26

6

3

-0.23

4

28

-0.90

7

20

0.62

5

20

0.81

8

21

0.25

6

18

0.71

9

32

0.54




10

38

-0.42

It is apparent from the results of Chen Zhihua et al. (1994) shown in Table 6.3 that calves born in early parities are lighter in weight than those born to later-parity dams. However, unlike most results from "improved" cattle breeds, calves born to first-parity dams were not at great disadvantage. Similarly, the effects of age (as distinct from parity) show that young yak cows had calves slightly lighter in weight than those born to older cows - though the oldest age group started to show, as might be expected, a decline in the birth weight of its calves. The variation is not large (though statistically significant) and there are some estimates that disrupt a steady trend (e.g. the estimate of a relatively large negative effect of fourth parity). It is not clear, however, how accurately an analysis such as this can estimate the effects of parity and age of the dam when both factors are included at the same time, as the two are partially confounded. Some aberrant values are not surprising.

Body weight of cow. According to Zhang Rongchang's observations in Tianzhu White yak (personal communication, 2000), calf birth weight is highly related to the mother's body weight. In his study, yak dams weighing less than 200 kg produced young of around 15.2 kg at birth (n=27), while newborn from yak dams weighing 201 - 230 kg and those weighing above 231 kg had offspring of about 16.4 kg (n=41) and 16.9 kg (22), respectively.

Other effects on birth weight and growth

Month of calving. Most calves are born from April to July, with May the peak month. Birth weight varies to some extent with month of calving (Table 6.4), as shown by the experiment at the Longri Breeding Farm in Sichuan, mentioned previously. As in respect of Table 6.3, and for the same reason, the results in Table 6.4 are presented as deviations from the overall least squares mean.

Apart from the unexpectedly low birth weight of calves born in the first half of June, there is a steady increase in birth weight from the middle of April to the middle of July, with all birth weights after mid-June above average and those of calves born before that below average. The variation in birth weight attributable to date of birth (as defined) was shown by Chen Zhihua et al. (1994) to be statistically highly significant (P<0.01).

Variation in birth weight with month of calving was also noted by Cai Li in F1 (Pian Niu) calves (hybrids of yak and cattle) born at Xiangdong Yak Farm in Ruoergai county of Sichuan. Average birth weight rose from 21.7 kg, for calves born in April, to 24.3 kg, for those born in June.

Table 6.4 Effect of date of calving on birth weight shown as deviations from the least squares fitted mean (cf. Table 6.2). [Source: Chen Zhihua et al., 1994]

Period of calving (day and month)

Number of calves

Deviation of birth weight (kg)

Prior to 15.4

6

-1.28

16.4 - 30.4

29

-1.67

1.5 - 15.5

26

-1.49

16.5 - 31.5

23

-0.77

1.6 - 15.6

30

-0.98

16.6 - 30.6

18

1.08

1.7 - 15.7

14

4.02

16.7 - 31.7

12

1.09

However, calves born early in the season, March or April, have a longer suckling period ahead of them than those born later in the season. For example, Ma Zongxiang and Dou Yaozong (1982) reported that calves born in March - April reached an average body weight of 45.6 kg by October of that year, while those born in June had attained only 34.2 kg, on average. The calf's growth in the first six months of its life is very important to its subsequent survival over the first winter. Calves born later in the season have a poorer chance of survival over winter than those born earlier.

Seasonal growth of yak. Typically, weight gain in a healthy calf reared by its dam is almost linear over the first six months of life, but declines with the approach of winter; this is followed by some loss in weight over the first winter and spring. Thereafter, in the second warm season, there is again a rapid gain in weight followed, once more, by a loss in weight over the next cold season.

Figure 6.1 illustrates growth from birth to 25 months old of 12 male and 12 female calves of the Plateau type born in April at Longri Breeding Farm of the Pasture Institute of Sichuan. Daily gain for the male calves was fairly constant over the first five months and declined rapidly thereafter. For female calves, weight gain for the first five months was somewhat more variable before declining over winter. In consequence, the weight of the calves increased linearly up to about five or six months of age before remaining more or less unchanged until the following warm season. In the second warm season after birth, weight gains from April/May to August/September were a little faster than in the first year, at between one third and one half kg per day. The third warm season started again with substantial gains in weight after the losses in the previous winter.

Figure 6.1 (a) Body weights of 12 male and 12 female calves born in April at the Pasture Institute of Sichuan, from birth to 25 months old. (b) Daily gain of yak calves monthly from birth to 25 months old.

Similar results (Table 6.5) were obtained with calves of the Alpine type born in May at the Pengbo farm of Tibet (4 000 - 4 600 m a.s.l.), according to the report of Ma Zongxiang and Dou Yaozong (1981).

As shown in Table 6.5, the weight loss of calves over the first winter was around 12 - 15 percent of the weight before the onset of winter. Typically, over the following summer and autumn young yak regain their weight losses and may well double in weight before again losing, over the second winter of life, perhaps 25 percent of the maximum weight reached. The cycle of weight gain and weight loss continues throughout life. This is illustrated in Figure 6.2 by observations on 180 yak steers from birth to five years old (Lu Guanghui 1980). In fully adult yak, the weight loss in the cold season is roughly equal to the gain in the following warm season.

Table 6.5 Monthly change of live weight, monthly gain and daily gain (±SD) of calves (n=14) in cold and warm seasons in Tibet [Source: adapted from Ma Zongxiang and Dou Yaozong, 1981]

Season

Month

Age of calf (months)

Live weight (kg)

Monthly gain (kg)

Daily gain (g)

Warm season

July

2

21.1 ± 1.5

-

-

August

3

28.4 ± 2.0

6.3 ± 0.6

213.7 ± 21.1

September

4

35.2 ± 2.6

5.1 ± 0.8

180.3 ± 19.4

Cold season

October

5

39.0 ± 3.1

5.2 ± 1.0

168.2 ± 11.7

November

6

38.3 ± 1.8

-0.6 ± 0.3

-23.0 ± 5.1

December

7

37.2 ± 2.7

-0.4 ± 0.3

-13.3 ± 3.0

January

8

37.0 ± 4.0

-0.8 ± 0.4

-31.1 ± 1.2

February

9

37.5 ± 2.3

0.5 ± 0.3

16.2 ± 2.4

March

10

36.1 ± 1.4

-0.7 ± 0.4

-23.0 ± 3.0

April

11

37.4 ± 1.3

0.5 ± 0.2

17.0 ± 4.0

Warm season

May

12

32.3 ± 2.4

-5.4 ± 0.2

-188.7 ± 24.1

June

13

38.5 ± 3.0

8.0 ± 1.2

250.1 ± 25.0

July

14

45.3 ± 3.4

5.3 ± 1.0

184.5 ± 14.2

Effect of type of rearing on weight gain. The manner in which the yak calf is reared profoundly affects its growth. The three main classes are: 1) to give the calf exclusive access to the milk of its dam (the dam is not milked), 2) to milk the dam once a day and allow the calf the remainder, and 3) to milk the dam twice a day and allow the calf what remains. An additional category (a subdivision of the first class) is that dams that are not milked may a) be allowed to graze at night or b) not be allowed to graze if kept restrained overnight with the yak females that are milked.

Figure 6.2 Changes in the body weight of 180 yak steers from birth to five years old (the first weighting at the date of birth, then at the end of autumn and at the end of spring- start of warm season) [Source: modified from Lu Guanghui, 1980]

There are many studies on the effects of these rearing treatments on calf growth. There is generally a beneficial and quite large effect on calf growth when the calf has access to all the milk of its dam. Often, the largest difference is between calves allowed access to dams milked only once a day compared with those reared by dams milked twice daily. Weight gain under the former regime can be double that from the latter as in the study of Zhang Rongchang (1989) shown in Table 6.6. This is not, however, only a consequence of differences in milk intake by the calf (which are not recorded but estimated to be somewhat greater when the dam is milked only once a day). Normally, the calves are tethered when their dams are milked. When the dam is milked only once daily, the calf is tethered and kept apart from the dam for a relatively short time only and grazes and drinks water alongside the dam for most of the day. Calves with dams milked twice a day are tethered for much of the day and have perhaps only four to five hours of time during which they move around at pasture with their dams. In a similar study by Yang Rongzhen et al. (1997), the main difference in growth of calves was between those from dams not milked compared to those milked - with, unusually, no effect due to frequency of milking. In this study, calves at the age of 18 months weighed around one third less if their dams were milked than if they were not milked.

Table 6.6 Live weight and daily gain (±SD) of calves with different rearing methods [Source: adapted from Zhang Rongchang, 1989]

Age (month)

Sex

No.

Not milked

Milked once daily

Milked twice daily

Live weight (kg)

Daily gain (g)

Live weight (kg)

Daily gain (g)

Live weight (kg)

Daily gain (g)

Birth

M

32

15.4 ± 3.5

-

15.9 ± 2.4

-

16.7 ± 1.3

-

F

30

17.8 ± 2.9

-

17.3 ± 4.0

-

15.4 ± 2.4

-

6

M

32

120.1 ± 13.2

558.3 ± 33.2

100.4 ± 9.1

482.3 ± 21.4

55.9 ± 5.6

229.8 ± 12.5

F

30

110.9 ± 10.2

533.1 ± 24.6

98.1 ± 5.6

456.9 ± 18.3

54.4 ± 3.4

215.2 ± 15.8

12

M

30

142.2 ± 7.8

349.9 ± 21.1

115.6 ± 7.7

287.2 ± 20.0

87.9 ± 7.2

194.2 ± 10.7

F

30

125.3 ± 12.6

303.3 ± 19.3

110.0 ± 4.9

256.1 ± 14.3

84.3 ± 8.8

192.8 ± 15.4

18

M

30

256.1 ± 18.5

440.1 ± 22.4

233.6 ± 12.3

402.1 ± 23.9

160.1 ± 6.9

276.0 ± 20.1

F

30

212.2 ± 14.3

383.4 ± 15.5

214.3 ± 10.2

366.1 ± 21.1

155.8 ± 9.7

255.6 ± 23.5

In another group trial conducted by Cai Li in Sichuan (at 3 450 m altitude), the six-month weight of calves from dams milked once a day was 93.1 kg compared with 48.5 kg for those with dams milked twice daily. At the Datong cattle farm in Qinghai, calves with dams that were not milked weighed 104.7 kg at six months old compared with 70.2 kg for those with dams milked once daily. Clearly, milking the dams and the associated separation of the calf from its dam adversely affected the weight gain of the calves.

Some calves suckle their dams for a second year and are not weaned until the end of the second warm season of their life. The dams lactating for that second season are those that have not calved again. Table 6.7 shows some results on a method of rearing on calf growth over a period of 92 days during their year of birth and then in the second year. (The results for the second year are all based on calves from dams that were milked once daily in the year in which their calf was born. In this trial, the females not milked were further divided into those that were confined at night along with their calves and those allowed to graze at night as well as during the day.)

It is seen that the additional grazing allowed to the dams and calves at night led to a substantial increase in the weight gain of the calves. Compared to the growth of calves confined at night along with their dams, milking of the dam once a day had no further detrimental effect at either age of calf - but milking twice a day and the attendant further restrictions on the calf reduced calf growth further (data for year of birth only). This seems to contrast with the larger effects of milking the dam, noted earlier, in the results of Zhang Rongchang (1989) and Cai Li (however, it is not explicitly stated for those studies whether the calves or their dams were confined at night or not). In view of the large, adverse effect of night confinement on calf growth shown in Table 6.7, it should be said that there are good reasons, apart from tradition, why it may not be possible everywhere to adopt a practice of night grazing for the calf alongside its dam. Thus, in many areas, yak calves need to be confined at night for reasons of safety and, if feasible, to provide their dams an undisturbed night's grazing prior to the morning milking.

Hand rearing of yak calves is restricted to situations where there is no alternative. Usually when a calf has lost its dam, it is fostered on a yak cow that has lost her calf (see Chapter 8). Data on the effects of artificial rearing on growth have not been obtained.

Breed and sex differences in growth. It is generally accepted that yak of the Alpine type, and especially the Jiulong breed (perhaps the best of the Alpine type), grow more rapidly than those of the Plateau type.

Table 6.7 Weight gain of yak calves in two successive years, according to rearing method [Source: Xu Guilin, 1985]

Dam

No.

Weight gain [92 days] (kg)

Year calf born (calf age 0 year)



Not milked - dam and calf confined

14

29.0

Not milked but grazing at night

17

60.8

Milked once daily

26

28.1

Milked twice daily

29

20.2

Year after calf born* (calf age 1 year)



Not milked - dam and calf confined

32

28.8

Not milked but grazing at night

9

49.8

Milked once daily

27

29.7

* The results are all based on calves from dams that were milked once daily in the year in which their calf was born.

The cautionary note has to be repeated that, normally, these different types and breeds are not at the same location at the same time and that yak type or breed are therefore confounded with location and the environmental differences implicit in that. This applies to the data shown in Table 6.8.

The greater growth of the Jiulong yak compared with the Maiwa yak (Table 6.8) appears to be a function not only of a larger final weight but also a faster early growth rate relative to that weight (since these results do not extend beyond the age of six and a half years, it is not known whether the weights at that stage are true mature weights although herdsmen usually regard the animals as "mature" by that age - see ensuing explanations).

By three to three and a half years old, the Jiulong males described in Table 6.8 had reached nearly 58 percent of their six- to six-and-a-half-year-old weight while the Maiwa had reached only 41 percent (for females the corresponding percentages are 78 percent and 70 percent, respectively). However, it is not known how these results may have been affected by the different environments in which the two breeds were kept. It is nonetheless apparent from Table 6.8 that for each breed the females grew faster relative to their final ("mature"?) weight in the early years of life than did the males. However, the growth of the females slowed after they reached the age of about four years. The males still continued to increase in weight quite markedly after that age - to reach a substantially greater final weight than the females. The growth differences between the sexes are reflected by the practice of the herdsmen to regard females as suitable for transfer to the adult herd at the age of four, whereas males are not regarded as "mature" (and at the height of their powers) until the age of six or seven.

Table 6.8 Estimated body weights* of Maiwa and Jiulong male and female yak (at separate locations) from birth to six and a half years old and weight at each age relative to final weight* (weights in October/November of each year). [Sources: Maiwa - Chen Xaifei et al., 1981; Jiulong - Cai Li et al., 1980a]


Maiwa

Jiulong

Male

Female

Male

Female

Age (yrs)

No.

Wt (kg)

[SD]

% of final

No.

Wt (kg)

[SD]

% of final

No.

Wt (kg)

[SD]

% of final

No.

Wt (kg)

[SD]

% of final

Birth

77

13.4


3.2

71

11.9


5.4

27

15.9

2.3

3.6

24

15.0

2.5

5.0

1 - 1.5

84

65.9

2.2

15.9

82

67.0

11.3

30.2

34

145.3

20.8

30.7

35

124.9

25.2

40.2

2 - 2.5

33

120.1

19.7

29.0

35

119.6

28.5

53.9

18

208.6

25.5

44.0

21

189.6

29.4

61.0

3 - 3.5

30

170.7

25.8

41.3

61

154.8

28.5

69.8

3

272.6

25.6

57.5

11

243.1

23.2

78.3

4 - 4.5

15

302.3

49.5

73.1

73

181.9

21.2

82.0

11

312.5

19.2

65.9

26

269.7

18.3

86.8

5 - 5.5

10

375.3

69.8

90.7

40

188.7

42.6

85.1

7

386.0

20.1

81.4

9

283.1

33.9

91.1

6 - 6.5

17

413.8

67.0

100

21

221.8

25.9

100

38

474.1

38.8

100

10

310.6

26.9

100

* Final weight is that at 6 or 6.5 years old and is not necessarily the weight at full maturity.

The difficulty of interpreting data on size and other aspects of the performance of yak as presented here, and in the literature on the yak in general, rests on the fact, as already noted, that conditions under which yak are kept vary from locality to locality and between years and that these factors are also often confounded with the type or breed of yak and with the management system. This point is further exemplified by Sarbagishev et al. [1989] who note that yak in Kyrgyzstan are considerably larger than those in neighbouring Tajikistan because in the former country, yak are not milked but kept exclusively for meat production. Under good grazing conditions on state farms in Kyrgyzstan, the researchers recorded weight gains during 12-month fattening periods well in excess of 100 kg live weight per year. These gains were made both in the second year of life (107 kg for 248 yak) and the third year of life (126 kg for 87 yak) and they were only a little less in the year after that (92 kg for 11 animals). That these weight gains are markedly higher than those shown in Table 6.8 for Maiwa and Jiulong yak should occasion no surprise since the Maiwa and Jiulong were not specifically managed as "fattening" animals. The higher growth rates on the state farms in Kyrgyzstan illustrate, however, that yak do have a higher potential for growth than is sometimes realized in the predominantly harsh conditions in which they are normally kept.

Linear body dimensions

Height at withers, body length, chest and girth circumferences and the estimated body weight from linear body dimensions of adult male and female yak at different locations in China are presented in Table 6.9 (Zhang Rongchang, 1989). These data testify to the fact that the size and performance of yak vary with locations and the type or breed of yak kept at these locations. Generally, yak in Sichuan have the biggest body size and those in Tibet the smallest; and the yak of the Alpine type has a larger body size than that of the Plateau type.

Chen Zhihua et al. (2000) collated evidence on environmental factors and concluded that the annual average temperature and precipitation were the most important among the environmental (ecological) factors affecting growth of yak (see also Chapter 4). As evidence of the importance of the environmental factors on body size and growth, it is possible to point to differences in size and weight at similar ages of the same "breed" at different locations. This further reinforces the caution that must be attached to comparisons (such as breed comparisons) across locations. Correlations among the body dimensions were reported to be of the order of 0.3 - 0.5 and those of the linear dimensions with body weight in the range of 0.5 - 0.6 (P< 0.01) (Wen Yongli and Chen Zhihua, 1994).

Table 6.10 shows the increase in linear body dimensions over a period of years. As already noted in respect of body weight (cf. Table 6.8) the females mature earlier than the males, as apparent from the higher proportion of last observed size (four years old in this case) reached by each body dimension at each of the earlier ages.

Table 6.9 Linear body dimensions and body weight (±SD) of adult yaks of different types and breeds at different locations in China [Source: adapted from Zhang Rongchang, 1989]

Location

Breed

Sex

No.

Height at withers (cm)

Body length (cm)

Chest circumf. (cm)

Girth circumf. (cm)

Body weight* (kg)

Tibet

Alpine**

M

39

122.2 ± 3.5

142.0 ± 6.6

167.8 ± 6.4

18.9 ± 2.3

293.5 ± 20.4

F

529

110.1 ± 4.8

125.1 ± 3.9

150.4 ± 4.8

15.4 ± 1.2

197.1 ± 16.4

Plateau***

M

20

116.6 ± 7.9

141.3 ± 5.9

169.6 ± 5.9

18.4 ± 1.9

282.4 ± 23.8

F

225

103.3 ± 5.5

126.1 ± 6.8

145.2 ± 9.1

15.2 ± 1.0

187.9 ± 19.0

Yunnan

Zhongdian

M

23

119.1 ± 8.1

126.9 ± 11.6

162.2 ± 10.8

17.6 ± 1.1

234.6 ± 35.8

F

186

105.2 ± 5.3

117.1 ± 8.3

153.7 ± 22.9

16.1 ± 1.0

192.5 ± 27.5

Sichuan

Jiulong

M

15

137.5 ± 8.8

172.6 ± 13.4

218.6 ± 26.7

23.64 ± 1.5

593.5 ± 184.9

F

708

116.6 ± 4.3

140.3 ± 7.8

178.5 ± 7.8

18.2 ± 1.3

314.4 ± 38.6

Maiwa

M

17

126.0 ± 5.0

157.3 ± 10.4

193.4 ± 9.2

19.8 ± 0.8

413.8 ± 67.0

F

219

106.2 ± 4.5

130.7 ± 7.3

154.6 ± 11.6

15.57 ± 1.0

221.8 ± 25.8

Qinghai

Plateau***

M

21

129.2 ± 6.2

150.6 ± 5.98

194.4 ± 7.7

20.10 ± 1.1

444.0 ± 54.7

F

208

110.9 ± 4.9

131.9 ± 5.1

157.2 ± 6.3

15.8 ± 1.1

256.4 ± 81.2

Huanhu

M

14

113.9 ± 6.5

143.7 ± 14.9

169.0 ± 15.3

18.3 ± 2.3

323.2 ± 100.6

F

138

103.0 ± 0.3

123.8 ± 7.6

147.0 ± 6.9

15.4 ± 1.2

210.6 ± 34.5

Gansu

Tianzhu White

M

17

120.8 ± 4.5

123.2 ± 4.7

163.8 ± 5.5

18.3 ± 1.1

264.1 ± 18.3

F

88

108.1 ± 5.5

113.6 ± 5.2

153.7 ± 8.0

16.8 ± 1.8

189.7 ± 20.8

Gannan

M

31

126.6 ± 6.4

141.0 ± 8.4

187.9 ± 10.8

21.3 ± 2.2

355.1 ± 35.7

F

378

107.6 ± 5.6

118.8 ± 7.5

154.7 ± 6.9

16.3 ± 1.3

210.5 ± 26.4

Xingjiang

Bazhou

M

33

126.8 ± 6.2

140.1 ± 10.4

192.4 ± 11.8

20.7 ± 1.3

362.6 ± 22.6

F

265

110.7 ± 2.5

123.5 ± 5.7

171.2 ± 9.1

16.3 ± 0.7

250.4 ± 21.3

* Estimated from body dimensions to avoid possible confusion over the breed nomenclature used in this Table. **"Alpine" yak in southeastern Tibet normally regarded as home to the Jiali and Pali breeds. *** "Plateau" yak in northwestern Tibet normally regarded as home to the Pali breed.

Table 6.10 Linear body dimensions (cm ±SD) of yak at different ages [Source: Zhong Guanghui et al., 1996a]

Sex

Age (yr)

No.

Height at withers

Chest depth

Chest width

Hip width

Heart girth

Cannon bone circumf.

Rump length

Body length

M

1

226

94.8 ± 20.7

44.4 ± 6.0

20.1 ± 2.7

23.8 ± 3.0

119.7 ± 12.9

13.7 ± 1.0

31.9 ± 3.5

99.8 ± 8.3

2

155

104.4 ± 5.5

53.9 ± 5.4

23.9 ± 3.9

27.8 ± 3.3

138.5 ± 10.2

15.4 ± 1.1

36.1 ± 2.6

114.8 ± 7.9

3

116

110.9 ± 5.7

58.6 ± 5.1

25.8 ± 3.5

30.4 ± 3.3

153.6 ± 13.0

16.5 ± 1.1

38.9 ± 3.8

124.5 ± 12.9

4

91

122.4 ± 8.6

67.9 ± 7.8

32.3 ± 8.2

36.9 ± 6.8

177.6 ± 18.6

18.8 ± 1.9

45.0 ± 5.3

140.2 ± 12.6

F

1

220

91.5 ± 6.3

43.8 ± 5.3

20.2 ± 5.7

23.2 ± 3.0

117.4 ± 11.0

13.4 ± 1.0

30.4 ± 3.5

97.4 ± 8.7

2

157

101.6 ± 5.3

51.6 ± 4.3

23.7 ± 4.4

27.6 ± 2.8

134.3 ± 13.7

14.7 ± 1.0

34.9 ± 3.9

111.4 ± 11.4

3

181

107.1 ± 4.9

56.2 ± 3.7

24.5 ± 3.2

30.7 ± 3.6

147.6 ± 9.7

15.7 ± 0.9

37.5 ± 2.4

120.0 ± 6.7

4

190

110.8 ± 6.3

58.9 ± 6.0

25.4 ± 5.2

32.2 ± 3.4

153.4 ± 11.7

16.1 ± 0.7

39.0 ± 2.2

126.1 ± 7.6

5

160

112.1 ± 4.5

60.9 ± 3.2

25.8 ± 3.9

33.4 ± 3.4

158.1 ± 9.7

16.3 ± 0.6

40.3 ± 2.2

127.5 ± 11.2

Females at one year had reached between 5 percent and 10 percent more of their size at four years old than did the males. The results also show, as is well established in the literature, that some body parts such as height at withers and cannon-bone circumference, mature relatively earlier in life than do others such as chest depth and hip width (with body weight continuing to increase significantly even after the linear dimensions have virtually stopped growing).

Wen Yongli and Chen Zhihua (1994) published results on body dimensions of Maiwa yak that also show similar relative rates of maturity of the different body parts and of body weight and the relatively later maturity in males than in females.

In the yak, as in other bovines, the linear body dimensions show less seasonal variation in size than is found for body weight (a cubic measure of size). Results are shown in Table 6.11 - albeit over a period of only two years. Moreover, relatively early-maturing dimensions that are largely a function of skeletal size, such as height at withers, show less variability in size over the seasons (there was no decline in size over winter) than dimensions that mature later and also include, in the measurement, a greater proportion of muscle and fat (e.g. heart girth).

Table 6.11 Height at withers, body length, and heart girth of yak over a two-year period (measurements in cm. are given for the unweighted average of 12 male and 10 female animals) [Source: Sichuan Grassland Institute, 1982]

Age (month)

Height at withers

Body length

Heart girth

Birth

50.8

45.7

56.8

6

79.1

86.6

104.9

12

88.9

88.5

102.7

18

93.1

107.1

135.1

24

95.8

108.5

128.6


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