T.K. Mohanty1, M.R. Ansari2 and R.N. Pal1
1. National Research Centre on Yak, Indian Council of Agricultural Research (ICAR), Dirang-790 101, West Kameng District, Arunachal Pradesh, India
2. Animal Reproduction Division, Indian Veterinary Research Institute, Izatnagar-243 122, Bareilly (U.P.), India
Factors that adversely affect the productive potential of yak include low reproductive rate, low calf birth weight, premature births and high calf mortality under normal grazing and management conditions. In the present study, anatomical characteristic of placenta and its relationship with calf birth weight in yak was studied to investigate causes of low calf birth weight and high calf mortality. The average calf birth weight in the study was 12.44 ± 2.96 kg, which represented 6.41 ± 1.2% of average dam weight after calving. The average post-partum body weight of yak cows was 187.00 ± 26.98 kg, which was 20% less than the average female weight in breeding season. The average placental weight was 1.58 ± 0.49 kg. Total numbers of cotyledons in pregnant and non-pregnant horns were 45.00 ± 7.11 and 27.25 ± 4.06, receptively. Total cotyledon area was 1493.94 ± 327.37 cm2 and total cotyledon area/birth weight of calf was 123.02 ± 23.44. These results seem to suggest that malnutrition in the third trimester of pregnancy is the major cause of low calf birth weight and low placental weight.
Keywords: Birth weight, calf, placenta, yak
The reproductive rate of yak cows is low under normal grazing and management conditions. Yak females are not mated for the first time until they are 3 years old, and often not until 4 years. Gestation length is around 258 days on average and is shorter than that of cattle. Abortion and other causes of premature termination of pregnancy are between 5 to 10 per cent (Cai and Wiener 1995). The reproductive pattern of yak in Arunachal Pradesh follows the same pattern. Although there has not been any systematic study, field observations suggest that the reproductive rate is generally low under traditional grazing conditions (Pal 1993). The overall low productivity has been attributed to low reproductive rate, low calf birth weight, premature birth and high calf mortality. In Tianzhu White yak' gestation period has been estimated at 255 days, mean birth weight at 11.4 ± 1.9 kg and there is a positive correlation between calf birth weight and supplemental feeding during the cold season (Zhang et al. 1997).
In the present study, anatomical characteristic of placenta and its relationship with calf birth weight in yak was studied to examine the cause of low calf birth weight and high calf mortality.
In the experimental yak herd, sixteen placentas were collected immediately after expulsion for anatomical observation. The calf birth weight and placental weight were recorded for statistical analysis.
Placental weight and measurements are presented in Table 1 and the correlation between placental traits and calf birth weight are presented in Table 2. The average calf birth weight was 12.44 ± 2.96 kg representing only 6.41 ± 1.2% of the average dam weight after calving. The calf birth weight was slightly higher than that reported for Tianzhu White yak of China by Zhang et al. (1997) and for Sangla Velly yak of Himachal Pradesh, India, by Kailla et al. (1997). The average post-partum body weight of the yak cow (187.7 ± 26.98 kg) was 20 per cent less than the average adult female weight in the breeding season (May to October), which was likely due to winter stress and scarcity of green fodder during this period. The average placental weight was 1.58 ± 0.49 kg, which was similar to that previously reported for Tianzhu White yak of China. The total number of cotyledon in yak after birth ranged between 77 and 117 in the present study, a value similar to that for other large ruminants (Stephan 1971).
Table 1. Anatomical characteristic of placenta of yak and its relationship with calf birth weight.
Items |
Mean (+/- S.D.)1 |
After birth weight (kg) |
1.58 ± 0.49 (1–2.5) |
Calf birth weight (kg) |
12.44 ± 2.96 (7.5–15.5) |
Numbers of cotyledon |
|
a) Pregnant horn |
45.00 ± 7.11 (35.00–58.00) |
b) Non pregnant horn |
27.25 ± 4.06 (21.00–35.00) |
c) Total |
98.25 ± 11.13 (77.00–117.00) |
Placental length (cm) |
|
a) Pregnant horn |
64.88 ± 8.39 (56.00–80.00) |
b) Non pregnant horn |
34.63 ± 7.35 (21.00–47.00) |
c) Total |
85.75 ± 34.37 (77.00–117.00) |
Average Cotyledon area (cm2) |
20.55 ± 2.92 (16.38–23.88) |
Total cotyledon area (cm2) |
1493.94 ± 327.37 (1015.56–2053.68) |
Total cotyledon area/birth weight of calf |
123.02 ± 23.44 (96.61–162.39) |
After birth weight was highly positively correlated (r = 0.914) with birth weight of calves, indicating the influence of after birth weight and function on foetal growth. The total area of cotyledon had a positive correlation (r = 0.849) with the calf birth weight. There was also high positive correlation of average cotyledon area with after birth weight and calf birth weight (r = 0.949 and 0.943, respectively). However, the ratio of total area of cotyledon to calf birth weight was higher in our study compared to that of the Tianzhu White yak of China (Zhang et al. 1994) and many breeds of cattle. The expanded placental area of yak may be an adaptation to the low oxygen environment to facilitate adequate supply of oxygen and nutrients to the foetus. In sheep, Penninga and Longo (1998) reported different types of placentome in high altitude hypoxic singletons and changes in the placentome in spontaneous hypoxic singletons at mean sea level. Penninga and Longo (1998) classified placentome into four different categories ranging from the type associated with the high altitude hypoxic environment to that associated with the physiological hypoxic conditions at mean sea level. This may explain the high ratio of total area of cotyledon to calf birth weight in the present study of yak at high altitude hypoxic condition. To generate more detailed information about the adaptation of yak to high altitude, further studies in this aspect are required.
Table 2. Estimates of correlation between placental traits and calf birth weight.
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 | |
1. After birth weight |
1.000 |
|
|
|
|
|
|
| |
2. Calf birth weight |
0.914* |
1.000 |
|
|
|
|
|
|
|
3. Total placenta length |
0.267 |
0.046 |
1.000 |
|
|
|
|
|
|
4. Total number of cotyledon |
0.443 |
0.268 |
0.168 |
1.000 |
|
|
|
|
|
5. Cotyledon area pregnant horn |
0.845* |
0.776 |
0.113 |
0.752* |
1.000 |
|
|
|
|
6. Cotyledon area empty horn |
0.797 |
0.634 |
0.381 |
0.879* |
0.905* |
1.000 |
|
|
|
7. Average area of cotyledon |
0.949** |
0.943** |
0.126 |
0.457 |
0.918* |
0.768 |
1.000 |
|
|
8. Total area of cotyledon |
0.849* |
0.755 |
0.179 |
0.798* |
0.994** |
0.946** |
0.879* |
1.000 |
|
9. Total area/birth weight of calf |
-0.252 |
-0.511 |
-0.142 |
0.651 |
0.118 |
0.308 |
0.265 |
0.168 |
1.000 |
It is concluded that if yak are supplemented with concentrate and roughage during pregnancy, particularly in severe winter, calf birth weight and placental weight can be increased and this will result in reduced incidences of calf mortality.
Cai L. and Wiener G. 1995. The yak. FAO (Food and Agricultural Organization of the United Nations) Regional Office for Asia and the Pacific, Bangkok, Thailand. pp. 57–76.
Kailla O.P., Pundir R.K., Gupta S.C. and Nivsarkar A.E. 1997. Growth pattern of Sangal Velly yak. Indian Journal of Animal Sciences 67(7):620–621.
Pal R.N. 1993. Domestic yak (Poephagus grunniens L): A research review. Indian Journal of Animal Sciences 63(7):743–753.
Penninga L. and Longo L.D. 1998. Ovine placentome morphology: Effect of high altitude, long-term hypoxia. Placenta 19(2-3):187–193.
Stephan J.R. 1971. Embryology. In: Veterinary obstetrics and genital diseases. 2nd ed. Indian reprint 1982. CBS (College Book Store) Publication, Delhi, India. pp. 43–44.
Zhang Zhaowang, Cui Xian, Han Xiangmin, Xu Changlin and Zhang Rongchang. 1994. Anatomical and histological research on cotyledon of Tianzhu White yak. In:Rongchang Zh., Jianlin H. and Jianping W. (eds), Proceedings of the 1st international congress on yak held in Lanzhou, P.R. China, 4–9 September 1994. Supplement of Journal of Gansu Agricultural University, Lanzhou, P.R. China. pp. 300–303.
Zhang Zhaowang, Han Xiangmin, Cui Xian, Zhan Rongchang, Xu Changlin and Wang Yuchang. 1997. Observation of oestrus and parturition characteristic in Tianzhu White yak. In: Rongzhen Y., Xingtai H. and Xiaolin L. (eds), Proceedings of the 2nd international congress on yak held in Xining, P.R. China, 1–6 September 1997. Qinghai People's Publishing House, Xining, P.R. China. pp. 189–192.
