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ABSTRACT

Reproductive efficiency is a major factor affecting economy and profit of the dairy industry. The factors affecting it can be categorized as interval from calving to the resumption of estrus cycle, estrus detection efficiency and conception rate following service. The cent reproductive efficiency shows the yield of one calf per cow per year. Poor reproductive performance can be resulted due to low feed availability, improper estrus detection process. Genetic selection for high milk yield also substantiates low pregnancy rate in dairy cows. Therefore, nutritional management including transition cow management, control of infectious reproductive diseases, optimum reproductive management, adoption of suitable heat detection system and estrus synchronization could play key role in improving the reproductive efficiency in dairy cow. A more balanced breeding strategies incorporating genomic technologies with greater emphasis on fertility must be developed.

Keywords: Body condition score, Dairy cattle, Estrus, Reproductive efficiency

 

 

Factors influencing reproductive efficiency

Puberty and sexual maturity

Age of puberty and sexual maturity are key determining factors for fertility of animals. Onset of puberty and sexual maturity are due to complex interplay between genetic and environmental factors, including plane of nutrition, disease and season of birth. Exotic breeds of dairy cattle reach puberty at 30-40% of their adult body weight, compared with 60% for zebu heifers. Poorly fed heifers prior to puberty results in delaying the onset of puberty, high pregnancy losses, low milk production after parturition and will not be compensated by post pubertal feeding. Feeding high energy or high concentrate diets not only reduce the age at sexual maturity but also lowers the time period for attaining the age of first calving. The supplementation of different energy levels in the diet of heifers containing 16% protein and 3.0Mcal/kg energy is an effective key factor for the optimum growth rate from 13 to 18 month of age in heifers (Javaid et al., 2014).

Body Condition Score (BCS) and Reproductive Performance

Body condition scores (BCS) provide an indication of the energy status of dairy cattle which is also linked with reproductive performance. BCS measured early in lactation could be used as an indirect selection criterion for fertility as BCS between 1 and 4 months postpartum had a high genetic correlation with fertility (Dechow et al., 2004). Negative energy balance in a cow causes mobilization of body fat and muscle tissue resulting alterations in blood metabolite (Insulin like growth factor-1, non-esterified fatty acids, β-hydroxybutyrate) and hormone profiles (LH, FSH, Estradiol, progesterone). Thereby the follicular development and mainly the growth of dominant follicle is compromised. This is in response associated with postpartum anestrus, poor expression of estrus behavior due to altered follicular dynamics and reduced conception rate in dairy animals (Wathes et al., 2007).

Estrus detection efficiency and accuracy

Accurate and efficient detection of estrus plays important role in reproductive management of dairy animals. Successful recognition of estrus prior to the actual time of ovulation may augment conception rate in cows. Failure to estrus detection leads to increase in days open (calving to conception interval) which is also responsible for low conception rate. Selection of animals for high milk yield has declined the percentage of overt signs and duration of estrus. Heat stress reduces the length and intensity of estrus and hence the incidences of anestrous and silent ovulation are increased (Garcia-Ispierto et al., 2007). Heat stress decreases blood progesterone concentration, which is a major cause for abnormal oocyte maturation, implantation failure and finally early embryonic death in dairy cattle. During summer, the feed consumption is reduced and thereby, body metabolism decreases blood glucose and IGF-1 level, but increased concentrations of serum urea, adrenocorticotropin and prolactin level synergistically shows negative effect on LH pulse frequency. This is in conclusion compromises the follicular dynamics resulting in reduced concentration of estradiol which is associated with poor estrous behavior and sub fertility in dairy cattle.

Strategies for optimizing breeding management of dairy heifers

Breeding management

In our country, the genetic selection of the dairy cattle is based on Dam’s milk yield record. The milk yield and pregnancy rate had a negative genetic correlation due to which genetic improvement in the milk performance leads to decline in the reproductive performance. Hence during the selection of a dairy cow, other relevant traits including fertility such as calving interval and longevity along with milk yield must be considered simultaneously while formulating the selection index for genetic improvement in dairy cattle. Genetic improvement of female fertility can be achieved by indirect selection for longevity or body condition score, or by direct selection for traits such as daughter pregnancy rate in cows (Weigel, 2006).

Nutritional Management

Dry matter intake and energy balance during the dry period and post calving transitional period have a crucial influence on herd health, productivity and reproductive efficiency. To achieve early sexual maturity and high conception rates in dairy cows, optimum body weight and adequate body condition score (BCS) are needed at the time of breeding. Therefore, feeding and management strategies can be employed to ameliorate the extent of negative energy balance and ensure cows maintain adequate BCS. The traditional feeding practice should be modified by providing mineral mixture, concentrate and green forages. Thus, minimizing BCS changes pre and post calving, maintenance of optimal rumen function and adoption of strategies to prevent metabolic disorders are key management targets to improve health, productivity and reproductive efficiency of high yielding dairy cows. A body condition score of 2.5 to 3.0 is desirable for heifers from six months old up to breeding age. Maintaining BCS between 3-3.5 in dry cow and postpartum period increases the postpartum reproductive efficiency by increasing the postpartum conception rate (Roche, 2006). 

Transition period in dairy cows is defined as the last three weeks before and the three weeks after parturition. This period is characterized by tremendous metabolic and endocrine challenges related to parturition and the onset of lactation. Therefore, a good nutritional management system ensuring BCS at drying off (3.0) and pre-calving (3.25) during the dry and transition period is important to reduce the incidences of metabolic diseases in cows. The feeding strategy of including supplemental by-pass fats can alter the fatty acid profile in the blood of cows and increase linoleic acid which in turn increases prostaglandin F2α (PG F2α) synthesis. PGF plays an important role in uterine involution in the transition period with consequence beneficial effects on fertility (Thatcher et al., 2006).

Reproductive Management

Efficient detection of estrus can increase pregnancy rate in dairy cattle. Therefore, accurate and efficient detection of estrus is a key factor for improving reproductive efficiency in cows. Now a days the use of heat detection aids such as pressure sensing systems, pedometers, video cameras, recording of vocalization as well as measuring of body temperature and milk progesterone concentration can support the herd managers in determining the onset of estrous (Reith and Hoy, 2018). Along with visual observation of estrus, synchronization of estrus with use of reproductive hormones also increases the conception rate among anestrus cows. Different protocols are used i.e., ovsynch, presynch, cosynch, selectsynch, doublesynch and heatsynch in order to bring a large percentage of group of females into estrus at a predetermined time through manipulating the length of luteal phase of estrus cycle (Knight et al., 2001). The length of the luteal phase can be shortened by treatment with prostaglandin F_2α or its analogues or it can be lengthened by treatment with exogenous progestagens. In addition, other hormones, such as gonadotropin-releasing hormone and estrogens, have been incorporated into some programs to reduce time of onset of estrus and to improve conception rate by manipulating follicular wave development.

Conclusion

Reproductive efficiency is an useful parameter for profitability in dairy industry. Nutrition plays a pivotal role in determining fertility of postpartum cows as negative energy balance during the transition period may enhance the incidences of metabolic diseases in cows. Thus, strategies are required to improve the reproductive efficiency of dairy cows through suitable feeding systems to reduce negative energy balance and to maintain proper body condition score of the animals. In addition, the herd management system should focus on oestrus detection efficiency to improve the conception rate in cows. For anestus and repeat breeder case, emphasis should be given for estrus synchronisation by the use of hormone supplements to improve the herd pregnancy rate. Appropriate breeding management strategy should be formulated to develop the selection index through including the fertility parameters for selection of the genetically more fertile dairy cows that will lead to decrease age at sexual maturity, age at first calving, calving interval and number of services per conception. Minimizing physiological and environmental stress such as heat stress, postpartum complications i.e., retained placenta, endometritis, mastitis and cystic ovaries also improve reproductive efficiency and overall production capacity of dairy animals.

References

Dairy Industry Vision 2030, 8^th series International animal industry expo. http://www.academia.edu/7433440/Indian _Dairy_Vision_2030.

Department of Animal Husbandry and Dairying (DAHD). Annual Report 2021-2022. New Delhi: Ministry of Fisheries, Animal Husbandry and Dairying.

Dechow, C.D., Rogers, G.W., Klei, L., Lawlor, I.J. and Vanraden, P.M. (2004). Body condition scores and dairy form evaluations as indicators of days open in US Holsteins. Journal of Dairy Science, 87: 3534-3541

Javaid, S., Sadiq, N., Anjum, M.I. and Lund, J. (2014). Effects of various weaning diets contained varying protein and energy levels on growth performance and nutrient digestibility in Red Sindhi calves. International Journal of Veterinary Science, 4: 22-25.

Knight, T.W., Lambert, M.G. and Devantier B.P. (2001). Calf survival from embryo transfer-induced twinning in dairy-beef cows and the effects of synchronised calving. Animal Reproduction Science, 68: 1-12.

Kumar, P., Purohit, G.N. and Mehta, J.S. (2018). Incidence of reproductive disorders in dairy cows. Intas Polivet, 19(1): 29-32.

Reith, S. and Hoy, S. (2018). Review: Behavioral signs of estrus and the potential of fully automated systems for detection of estrus in dairy cattle. Animal, 12(2): 398-407.

Roche, J. F. (2006). The effect of nutritional management of the dairy cow on reproductive efficiency. Animal Reproduction Science, 96: 282-296.

Thatcher, W.W., Bilby, T.R., Bartolome, J.A., Silvelstre, F., Staples, C.R. and Santos, J.E. (2006). Strategies for improving fertility in the modern dairy cow. Theriogenology, 65: 30–44.

Wathes D.C., Fenwick M., Cheng Z., Bourne N., Llewellyn S., Morris D.G., Kenny D., Murphy J. and Fitzpatrick R. (2007). Influence of negative energy balance on cyclicity and fertility in the high producing dairy cow. Theriogenology, 68: 232-241.

 

Weigel, A. (2006). Prospects for improving reproductive performance through genetic selection. Animal Reproduction Science, 96: 323-330.

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