Prediction of Viability of Cows: a New Look at the Old Problem

The use of intensive technologies in industrial livestock breeding has led to a reduction in the level of biodiversity, an increase in disease incidences and decline in reproduction. In dairy cattle breeding, the main efforts now are directed at control of morbidity, but solution of problems may be in another area, related to an increase in the overall viability of populations. The problem is to find the quantitative tests for early evaluation of the desired traits for targeted selection. The aim of this work is to present several methodological approaches for quantifying the viability of cows at the level of group (e.g., bull’s daughters), herd or population.


Introduction
The use of intensive technologies in industrial livestock breeding has led to an increase in negative trends, including a reduction in the level of biodiversity, an increase in disease incidences and decline in reproduction. In dairy cattle breeding, the main efforts are directed at the treatment of diseases of lactating animals, although the solution of problems may be in another area, not related to the treatment of sick animals, but to an increase in the overall viability of populations. It is known from practice that a good cow can be obtained only from a good heifer. Researchers know the phenomenon of "primal health" [1], so we should learn identify at a young age the long-standing groups with a high potential for protective functions and the ability to lactate. With the use of modern methods of large-scale selection of animals, the desired type of cattle can be obtained over several generations, when an effective quantitative test is known for early evaluation of the desired trait in the offspring. The problem is to find directions for research to develop such tests.
It is known that in critical periods of early development, external influences cause shifts in the emerging systems that can persist throughout life [2,3]. Mediating factors can influence gene expression without affecting the coding sequences of DNA, however, changes in expression patterns can sometimes be transmitted to offspring in some cases [4]. Potential candidates for the role of tests for assessing the viability potential should not be sought in terms of physiological homeostasis; they are more likely to be found in the area of long-acting factors of constitutive resistance [5]. For productive animals, term "constitutive resistance" can be interpreted as the age-dependent functional capacity to ensure productive longevity and fertility. Similar problems are now being investigated in the field of personalized predictive medicine [6,7]. The aim of this work is to present several methodological approaches for early quantifying the viability of cows at the level of group (e.g., bull's daughters), herd or population.

Assessment of parameters by the age dynamics of milk yield
The data of the milk yields for 305 days ( ) , the peak of 305-d milk yield comes earlier and the cows drop out faster from the herd. The level of peak of milk yield is always less than A by a quantity that depends on the rate of decrease in constitutive resistance.
The study of data obtained for herds of several breeds revealed a positive relationship between the length of productive life (LPL) in groups of cows with the same number of the last lactation, and the corresponding values of D for these groups

Abstract
The use of intensive technologies in industrial livestock breeding has led to a reduction in the level of biodiversity, an increase in disease incidences and decline in reproduction. In dairy cattle breeding, the main efforts now are directed at control of morbidity, but solution of problems may be in another area, related to an increase in the overall viability of populations. The problem is to find the quantitative tests for early evaluation of the desired traits for targeted selection. The aim of this work is to present several methodological approaches for quantifying the viability of cows at the level of group (e.g., bull's daughters), herd or population.  [5]. The presence of a positive relationship between D and LPL indicates that the duration of the economic use of cows is determined to a certain extent by the level of constitutive resistance at first lactation.

Assessment of parameters by dynamics of culling rate of cows
A similar relationship has been revealed when analyzing the dynamics of survival of cows in a herd. The dynamics of culling rate of cows from the herd (culling intensity from respective cohort when herd is in stationary state) in most cases is well approximated by the Gompertz function ( ) c y t (Figure 1):  divided by the number of cows on first lactation). When analyzing the survival dynamics of cows in herds of several breeds, the existence of a positive relationship between LPL and 1/y c1 was revealed [5]. So, 1/yc 1 , , in meaning is identical to t D and parameters D and 1/y c1 may be considered as candidates on the role of predictors of LPL.
These interrelationships are compatible with concepts well known in the biology of aging. In all animals, after entering the reproductive period, an exponential increase in the death rate is observed and, accordingly, an exponential decrease in the reciprocal of this value, i.e. in the level of viability, so that at definite time the organism comes into the range of values of key parameters that are incompatible with life. Figure 2 illustrates this situation for two cohorts of cows with the same value of c and two levels of B in the Gompertz function.

Conclusion
The revealed interrelations provide a definite basis for understanding the factors that determine the age dynamics of viability and milk productivity of cows. The critical factor for longevity of dairy cows is the "initial" value of viability (primal health, initial constitutive resistance), that animals acquired at the onset of reproductive period. Therefore, in addition to the current struggle against diseases, the long-term research and developments must be performed aimed to increase the primal health of breeding stock. From this view-point, the targeted breeding, elimination of adverse influences during embryonic, fetal and postnatal development, and good technologies for the growing of heifer can increase the viability of cows and milk productive performance.