Genetic selection of economically important traits in dairy cattle
Snehasmita Panda1*, Junaid Kar2, Prachurya Biswal3, Mitek Tarang1, B L Saini1, M Monika4
1PhD scholar, Division of Animal Genetics, IVRI, Izatnagar, Uttar Pradesh
2Veterinary assistant surgeon, Department of Sheep Husbandry, Jammu & Kashmir
3PhD scholar, Livestock Production Management Section, IVRI, Izatnagar, Uttar Pradesh
PhD scholar, Poultry science, CARI, Izatnagar, Uttar Pradesh
*Email id – sneha23437@gmail.com
INTRODUCTION
In India the focus of selection in dairy cattle population is purely production oriented. However, a more balanced breeding goal can be achieved by considering some novel traits for selection in dairy cattle populations. Methodological advances in both genetic theory and statistics with technological innovations in computing, paved the way for powerful multitrait analyses. Increased concern towards significant issues like health and fertility of dairy cattle emphasized introduction of traits i.e., longevity, fertility, calving, health, and workability into selection indices. Current research focuses on fitness, health, welfare, milk quality, and environmental sustainability, underlying the concentrated emphasis on a more comprehensive breeding goal.
A potential trait must meet several criteria before it can be considered for selection in dairy cattle populations. First, either it should have an economic value. Second, the trait must have sufficiently large genetic variation and heritability. An indicator trait may be favored if it has a high genetic correlation with the economically important trait, reduces recording costs, has a higher heritability, or can be measured earlier in life. Third, the trait should be clearly defined, measurable at a low cost, and consistently recorded.
Here are some of the important traits need to be addressed in genetic selection program of cattle industry in India.
1. Production – In India selection in dairy cattle is focused on high milk and fat production. Male line has received the greatest attention in selection because the sire’s heredity was most accurately indicated by his daughters’ production, more than the dam based on her own production record. Traits also considered by breeders to aid in the selection of animals to improve production were milk protein yield, lactation length, dry period, persistency, peak yield and test day milk yield. Production traits are mostly moderately heritable and estimates for milk yield, fat yield, protein yield, fat percentage and protein percentage were 0.30, 0.32, 0.33, 0.42 and 0.44 respectively.
2. Fertility – Because of the economic importance of reproductive efficiency, much attention has been given to fertility traits. Number of services required for conception, non returns to first service, the interval from calving to first insemination, and calving interval are measures fertility. Because of the low heritability of fertility traits and the difficulties related to their measurement, indicator traits could be very useful for increasing accuracy of estimated breeding values. Novel phenotypes, such as Body Condition Scoring and mid-infrared (MIR) predicted fatty acid profile in milk have been proposed as indicator traits for fertility.
3. Conformation – Favourable genetic correlation between confirmation and production, as well as with fertility traits highlighted inclusion of these traits in genetic selection. Udder conformation traits showed positive correlations with milking ability and with udder health. Body length, height at withers, height at shoulder, height at knee, heart girth, punch girth, face length, face width, horn length, horn diameter, distance between horns, ear length, ear width, neck length, neck diameter, tail length with switch, tail length, stature, udder depth, teat length, udder texture are some of the major confirmation traits. The heritability estimates reported for conformation traits were moderate to low.
4. Longevity – It is defined as length of time a cow remains in the productive herd or its ability to remain in the herd. Measures of longevity have included age at last calving, number of lactations, and survival to a fixed age. Main goal in selecting longevity is to reduce the costs of replacements and maximizes the profitable period. In addition, improving longevity could aid in breed development and genetic improvement because it would allow for more voluntary culling and greater selection intensity. In general, the heritability of longevity in dairy cows is low. To overcome this, early measure for indirect selection for longevity need to be investigated.
5. Calving – Calving difficulty and calf mortality represent major problems affecting profitability of dairy farming, especially if the dead calf is female. Heritability estimates of different calving traits i.e., dystocia and calf size are 0.08 and 0.15, respectively.
6. Health – Diseases in dairy cattle are a major source of economic loss for dairy producers. Although there is a large effect of environment and management on disease occurrence, variation between cows can be observed. Mastitis, ketosis, lameness, cystic ovaries and metritis are economically significant disease affecting the dairy industry. Somatic cell count and acetone are considered to be an indicator for mastitis and ketosis respectively. Heritability estimates for these traits are low.
7. Workability – Most important workability traits are temperament (general temperament, milking temperament, aggressiveness, rank order in herd) and milking speed. Heritability estimates presented for temperament ranged from 0.08 to 0.25.
NOVEL TRAITS
1. Feed efficiency – Generally, feed efficiency describes units of product output per unit of feed input and measured by residual feed intake (RFI). Heritability estimates for RFI in lactating cows range from 0.01 to 0.40. A negative genetic correlation was found between gross feed efficiency and energy balance.
2. Methane emissions – Mitigation of enteric methane emissions in ruminants has become an important area of research because methane is strongly linked to global warming. Several methane emission related variables include feed intake and feeding behavior, rumen function, metabolites and microbiome (rumen microbiota and host–microbiome interactions), milk production and composition, hindgut and feces. Several studies have confirmed that methane emission is a moderately heritable trait ranging from 0.21 to 0.35
3. Heat stress – In a world with a changing environment, breeding robust dairy cows will likely become an important activity in the near future. Tolerance to heat stress has been shown to be heritable, ranging from 0.17 to 0.33
4. Hoof health – Effect of lameness on milk production and dairy cow survival, indicated the importance of hoof health for the dairy industry. Heritabilities of individual hoof lesions have ranged from 0.01 to 0.13
5. Immune response – The immune response or ability to resist infections and diseases is a complex trait. Cellular immune-associated traits are heritable and repeatable. Estimates of heritability for immune response traits are high (0.25–0.35).
6. Milk composition – The genetic variation in the composition of milk is of interest because of its effect on the nutritional value and technological properties of milk. Fatty acid and mineral concentration of milk has been shown to be under genetic control. Heritability of milk fatty acid contents tends to decrease with an increase in carbon chain length. In addition, saturated fatty acid is more heritable than unsaturated fatty acid.
7. Milk coagulation properties – Milk coagulation property traits have become of interest to the dairy industry because of the cheese sector. The physical characteristics of milk such as rennet coagulation time, curd firmness 30 min after rennet addition, and curd firming time are important milk coagulation traits.
8. Reproductive technology traits – In the last decades, super ovulation and embryo transfer have been widely used around the world to increase the genetic contribution of elite females. A low to moderate maternal heritabilities for number of flushed ova, transferable embryos, degenerated embryos, unfertilized oocytes, and percentage of transferrable embryos has been reported.
Conclusion
India has seen 1.5-fold increase in milk production within 10 year i.e., 266 million tonnes in 2008-09 to 394 million tonnes in 2018-19. This is one of the most successful stories of improvement in livestock production attributable to enhanced management, feeding, and genetics. However, inclusion of above discussed traits in selection indices with a balanced breeding goal will produce a more desirable genetic progress with the introduction of genomic selection in Indian dairy industry.
