Discipline: reproduction; Key words:concentrate level, crossbreeding, days open, energy source, interval traits, genetic parameters, management-induced infertility.
The fertility of dairy cows is arguably the most important factor affecting the genetic improvement and financial sustainability of a dairy herd. However, fertility in dairy herds (primarily Holsteins) worldwide has declined in recent years as milk yield has increased. A reason for the decline in fertility could be that breeding and selection programmes in dairy herds have focused on the improvement of milk yield and conformation traits, whereas little emphasis has been put on genetic improvement of fertility. This is probably because fertility is a complex trait that is affected by a number of factors. Genetically, it is difficult to change because of its low heritability. Therefore the way low fertility is addressed is that cows that do not become pregnant are culled on farm. This put a large responsibility on farm reproduction management. Poor management may result in poor fertility because, as example, cows may come on heat but are not inseminated owing to poor heat observation. On the up side though, because of veterinary interventions such as hormonal treatments to activate heat cycling, the probability of cows becoming pregnant increases because of timed inseminations. Both practices have direct and indirect cost implications for farmers and also complicate efforts to select for improved reproduction. To observe trends in South Africa, the objective of the study by the authors cited below was to review results from studies conducted in South Africa which were aimed at improving the reproductive performance of Holstein cows. It should be emphasized that the sample of herds selected cannot be regarded as representative of the general trend in the country. It nevertheless provides valuable information.
Artificial insemination records from 9 046 cows in 14 Holstein herds were obtained for the study. Standards and norms were established to determine the level of reproduction management. Genetic parameters for fertility traits based on service records were also estimated. In addition, two studies were conducted to quantify the effect of crossbreeding using a dual-purpose breed and in a third study the effect of concentrate feeding level and concentrate energy source on fertility of Holsteins was investigated.
The results showed that, while lactation number, year of calving and calving season affected fertility traits significantly, herd management had the largest effect. The mean (and coefficient of variation as a % of the mean) for calving to first service (CFS) and from calving to conception (days open [DO]) intervals were 77 (39%) and 134 (55%) days, respectively. The number of services per conception (SPC) was 2.55 (70%). The proportion of first services within 80 days post partum and cows confirmed pregnant within 100 and 200 days post partum were 0.64 (75%), 0.36 (133%), and 0.71 (63%), respectively. The results showed that the between-herd variation in these critical parameters is large. Heritability (h²) estimates were 0.06, 0.08 and 0.07 for CFS, DO, and SPC, respectively. The low h² estimates are consistent with literature results. The genetic correlation between CFS and DO was positive (0.56), and negative (-0.29) between CFS and pregnancy success. Crossbreeding, using a dual-purpose breed, improved fertility, similar to studies conducted elsewhere. By increasing the energy content of the total diet of Holstein cows on kikuyu-ryegrass pasture from feeding 7 kg to 12 kg concentrates per cow per day, improved fertility as a higher proportion of cows were pregnant by 150 days in milk, being 52% versus 84% and 56% versus 76% for first-calf and multi-lactation cows, respectively.
Conclusions and recommendations: This review demonstrated possible interventions to improve the fertility of dairy cows. It showed the possibility of estimating genetic parameters for fertility traits using farmers’ service records that are generally used in herd reproduction management. A larger dataset than the present study would improve the robustness of the results. A number of automatic recording systems are used by dairy farmers for herd management. Access to records from these herds would make it possible to establish a national database. However, it is important that similar fertility traits to those in other major dairying countries are used. This would enable South African results to be compared with international standards. The results also suggested that managerial interventions through crossbreeding and nutritional changes could affect the reproductive performance of dairy cows. Further work on these topics in South Africa is required. A standard of reproduction management of dairy farmers should be established, as the large coefficient of variation in critical parameters is unacceptable and confusing, as it gives the impression of infertility in otherwise fertile cows.
C.J.C. Muller, S.W.P. Cloete & J.A. Botha, 2018. Fertility in dairy cows and ways to improve it. S. Afr. J. Anim. Sci. 48, 858-868.