| Livestock Research for Rural Development 29 (3) 2017 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
Stayability in terms of lactation-specific survival/disposal pattern in a herd of cattle is useful in evaluation and formulation of breeding programmes. This study was undertaken to analyse lactation specific demographic parameters of Jersey x Red Sindhi crossbred cows under North Eastern agro-climatic conditions of Tamil Nadu, India.
Data on 355 Jersey x Red Sindhi crossbred cows maintained at Post Graduate Research Institute in Animal Sciences, Kattupakkam, were used. Survival rate of adult cows reaching first lactation to survive until next lactation was 65 %. The expected herd life was calculated to be 1.47, 1.08, 0.42, 0.25 lactations in first, third, fifth and eighth parities. The probability of cows being lost from the herd due to their death and culling was 0.35, 0.13 and 0.08 at first, fourth and eight lactations, respectively. Results are indicative of lesser stayability of cows in terms of number of lactations, which can reduce production efficiency in the herd.
Key words: culling, expected herd life, stayability, survival rate
Jersey breed of cattle is recommended for crossbreeding in most parts of India. Studies evaluating the production and reproduction performance of Jersey crossbreds in India are available but more studies on fitness traits like survivability are necessary to understand the adaptability of the genetic group to different agro-climatic conditions. Lactation specific demographic parameters have been used as a measure of stayability of productive dairy animals in a lactation scale (Greer et al 1980). The lactation-specific survival/disposal pattern, herd structure, expected herd life and overall lifetime statistics in a herd of cattle are important, as these are required to formulate, operate and evaluate a breeding programme for genetic improvement. These parameters will help in developing models to optimize culling and replacement rates and to have a check on management practices for better production and reproduction of animals. The present study was carried out to analyse lactation specific demographic parameters of Jersey x Red Sindhi crossbred cattle under North Eastern agro-climatic conditions of Tamil Nadu, India.
The data on production performance records of 355 Jersey x Red Sindhi crossbred cows spread over a period of 25 years were collected from the history and pedigree sheets and registers maintained at the Post-Graduate Research Institute in Animal Sciences (PGRIAS), Kattupakkam and Tamil Nadu. The lactation-specific herd dynamics were estimated through the following parameters as described by Schons et al (1985) and Tomar et al (1996). Data were analysed using MTcrosoft Excel
(i) Stability (Lx): Defined as the probability of a cow at first lactation present in herd to lactation ‘X’ and calculated as number present at lactation ‘X’ divided by the number alive at first lactation. The stability at first lactation was taken as unity and hence L0 = 1.0.
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where,
nx = number of cows surviving at lactation ‘X’
n0 = number of cows at first lactation.
(ii) Survival rate (Px): It is the probability of a cow surviving to lactation X+1, assuming survival to lactation ‘X’, and estimated as:
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(iii) Disposal rate (Qx): This is complement of Px. It is the probability of a cow, dying or being culled before lactation x+1, assuming survival to lactation ‘X’, thus,
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where,
dx= number of animals died or culled during lactation x
nx= number of animals present in the herd at the beginning of lactation x.
(iv) Lactation-specific herd structure: Lactation-specific herd structure was calculated as described by Greer et al (1980).
Age-specific distribution of cow (ax): It is the probability of cows in each lactation,to remain in the herd and calculated as
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ax such that ∑ax=1.0
Age-specific loss (bx): It is the probability of cows being lost from herd that are of each lactation and estimated as bx= Qx Lx, such that .∑bx=1.0
(v) Expected herd life (Ex): This is the number of additional lactations that an animal of lactation ‘X’ is expected to remain in the herd (Ex more years) and it was estimated as the sum of probability of an animal of a given lactation remaining in the herd (Px) through each succeeding lactation up to the last lactation.
Ex = Px +Px Px+1 +Px Px+1 Px+2 +…….Px Px+1Px+n (Ahmed et al 1992) .
The herd dynamics of Jersey X Red Sindhi crossbred cows in terms of survival rate, stability, herd structure and expected herd life is presented in Table 1and Figure 1.
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Table 1. Lactation specific herd dynamics of Jersey x Red Sindhi crossbred cows |
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Lactation |
n |
Survival |
Disposal |
Stability |
Herd structure |
Expected herd |
|
|
Present in |
Disposed |
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|
1 |
355 |
0.65 |
0.35 |
1.00 |
0.40 |
0.35 |
1.47 |
|
2 |
234 |
0.62 |
0.38 |
0.66 |
0.26 |
0.24 |
1.08 |
|
3 |
146 |
0.60 |
0.40 |
0.41 |
0.17 |
0.15 |
1.08 |
|
4 |
92 |
0.48 |
0.52 |
0.25 |
0.10 |
0.13 |
0.73 |
|
5 |
45 |
0.28 |
0.72 |
0.12 |
0.04 |
0.08 |
0.42 |
|
6 |
13 |
0.53 |
0.47 |
0.03 |
0.01 |
0.01 |
0.90 |
|
7 |
7 |
0.57 |
0.43 |
0.01 |
0.004 |
0.004 |
0.71 |
|
8 |
4 |
0.25 |
0.75 |
0.01 |
0.004 |
0.08 |
0.25 |
|
9 |
1 |
0.00 |
1.00 |
0.002 |
0.001 |
0.002 |
0.00 |
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n - Number of observations |
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A survival rate of 65 % in first lactation, indicate that a cow surviving up to first lactation has 65 % chance of being insecond lactation. The loss rate was least in the first lactation (35 %) and hence the probability of survival rate was more (Table 1). Survival rate to subsequent lactations continuously decreased with increase in lactation number until fifth lactation, after which the values fluctuated and no definite trend of survival rate was observed.
Stability was found to decrease with lactation and became negligible after the fifth lactation. The proportion of animals of total herd present in first lactation was 40 %, while only 4 % were left out after the fourth lactation, after which values were negligible. It was observed that 93 % of total cows present in the herd belonged to first four lactations and less than 5.8 % cows belonged to fifth lactations and above. The probability of cows being lost from the herd due to death and culling was found to be 0.35 after first lactation, which means 35 % of cows left the herd by the end of first lactation.
Expected herd life in terms of number of lactations showed that a cow completing first lactation was expected to remain in the herd for 1.47 lactations more. The expected herd life decreased thereafter. Average expected herd life of cows up to third lactation was almost similar (1.2) and it was <1 lactation for the cows belonging to fourth and above lactations.
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| Figure 1. Trend of lactation specific demographic parameters |
Lactation specific demographic parameters help in understanding the survivability of cows and throws light on their culling and disposal pattern in terms of number of lactations
Higher survival rate than the present estimate was reported by Kumar et al (2012) for Frieswal cattle (76 %) and Shahi and Kumar (2012) for Sahiwal cattle (89.6 %) in the first lactation. There is no report on survival rate of Jersey crossbred cows and hence comparisons were made with the available reports in other cattle breeds.
Contrary to the present findings, Kumar et al (2012) for Frieswal cattle (2.05 %) and Shahi and Kumar (2012) for Sahiwal cattle (3.14 %) reported higher expected herd life at the end of the first lactation. Comparatively lower expected herd life for the present herd may be due to various management issues and culling policy.
All the lactation specific parameters indicate lower stayability of Jersey crossbred animals in the herd, given the conditions of management in the farm. . The reported differences between herds could be due to breed differences and differences in death and culling rates at different farms because of differences in management and culling policies. Apart from death, other reasons for disposal in the farm included culling due to disease, infertility and low productivity.The most important reasons for disposal observed in Dairy Herd Improvement Association of the USA(DHIA) herds were low production, 27-32%; sterility, 16-19%; udder trouble or mastitis, 14-20%; and sold for dairy purposes, 14-15% (O’Bleness’ and Vanvleck, 1962). A loss of 35 per cent of cows by the end of first lactation and expected herd life of 1.47 lactations show lower stayability, which can lead to higher replacement rate and consequently lower selection pressure for milk yield. Steps to improve stayability through interventions in management, is necessary to improve life-time production of the farm.
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Tomar S S, Rawal S C and Singh R B 1996 Population analysis for certain demographic parameters in Tharparkar herd. Indian Journal of Dairy Science 49: 562-566.
Received 18 September 2016; Accepted 10 January 2017; Published 1 March 2017