Factors influencing insemination per pregnancy in high and low forage dairy feeding systems

Cheryl Ashworth, Liveness Jessica Banda, Mizeck Gift G Chagunda, David J Roberts

Research output: Contribution to conferencePaperpeer-review


Introduction The modern high producing dairy cow has been associated with declining fertility, which has been attributed to the antagonistic genetic relationship between fertility and milk yield (Lovendahl et al. 2009) as well as differences in production systems and regions (McDougall 2006). This study was carried out to determine the influence of genetic merit, feeding system, body energy content and milk yield on the number of inseminations per pregnancy in cows under high and low forage feeding systems.

Materials and Methods The work was undertaken with a Holstein Friesian herd that comprised high (select) and average (control) genetic merit cows based on fat and protein predicted transmitting ability. The feeding system was either low or high forage diets with a target dry matter (DM) from forage of 50 and 75%, respectively. The low and high forage diets had metabolizable energy (ME) of 12.3 and 11.5MJ and crude protein (CP) of 185 and 180 g per kg DM, respectively. The genetic merit and feeding system formed 4 treatments - low forage select (LFS), low forage control (LFC), high forage select (HFS) and high forage control (HFC). A total of 1179 records from 383 cows between their first and fourth lactations and which calved between September 2003 and December 2010 were grouped according to the number of inseminations to achieve pregnancy. The groups were pregnancy with 1, 2, 3 and >3 inseminations representing 35, 23, 16, and 26% of the population, respectively. A general linear mixed model (GLIMMIX procedure) of SAS 9.2 at 5% probability was used to determine factors that influence the outcome of inseminations. Modeling of binary (pregnancy diagnosis results) data was done for all lactations with the cow as a random factor. The variable pregnancy diagnosis result was assigned a value of 1 if a cow was pregnant with the first three inseminations and 0 if the pregnancy occurred after more than three inseminations. The regression factors included genetic merit, feeding system, lactation number, days to first recorded heat (DFH), milk yield at service, calving and service body energy content.

Results The herd had more cows (48%) in their first lactation than cows in their second (28%), third and fourth lactation (24%). Cows that became pregnant after >3 inseminations had significantly (p<0.05) higher calving and service weight, service body energy content and condition score. There were no significant differences in DFH as well as days to first and last service between lactations. Genetic merit, lactation number, DFH, service body energy content and milk yield had significant effect (p<0.05) on pregnancy outcome with the first 3 inseminations. There was also significant interaction between genetic merit and feeding and hence these were combined and presented as a production system (Table 1). The odds ratio estimates in Table 1 show that LFC cows and cows in their first lactation have the highest chance of getting pregnant with the first three inseminations. LFC cows are 3.5 times more likely to get pregnant than HFS cows suggesting lower fertility in high genetic merit cows.

Table 1: Odds ratio estimates for pregnancy with the first 3 inseminations in cows under different production systems
Factor *Production system Lactation number Days to 1st recorded heat Service milk yield (litres) Service body energy content (MJ)
LFC LFS HFC 1 2 67 32 4498
HFS HFS HFS 3 3 66 31 4497
Odds ratio estimate 3.5 2.8 1.4 3.5 1.6 1.0 1.1 1.0
Lower CL** 1.857 1.607 0.777 2.063 0.966 1.001 1.046 0.999
Upper CL 6.711 4.899 2.599 6.088 2.622 1.015 1.110 0.999
*HFS=high forage select; LFS=low forage select; HFC=high forage control; LFC=low forage control **CL = 95% confidence limit

Pollot & Coffey (2008) associated genetic selection for high fat and protein levels in milk with increasing the time taken to start luteal activity post-partum. However, LFS cows had higher odds of getting pregnant than HFC cows. This could be attributed to differences in ME and CP available in the rations. Cows on low forage diet had higher CP and ME which might have contributed to higher odds of getting pregnant. A unit change in days to first heat, milk yield and service body energy content does not seem to have much effect on an insemination outcome.

Conclusion The results show that the feeding system plays an important role in determining the outcome of an insemination in dairy cattle. Cows fed rations with relatively lower CP and ME have a lower chance of pregnancy with the first three inseminations. Genetic merit, days to first heat, service milk yield and body energy content seem important in determining a chance of getting pregnant with the first three inseminations and these could probably be used to develop models for predicting pregnancy for each insemination.

Acknowledgements The authors appreciate funding from Flanders International Cooperation Agency and the Scottish Government.
Lovendahl, P., Chagunda, M., O'Connell, J., & Friggens, N. 2009. Cattle Practice, 17, 7-12.
McDougall, S. 2006. Journal of Reproduction and Development 52 , 185-194.
Pollott, G. E. & Coffey, M. P. 2008, Journal of Dairy Science vol. 91, no. 9, pp. 3649-3660.
Original languageEnglish
Number of pages1
Publication statusPublished - 2013
EventBritish Society of Animal Science Annual Meeting - Nottingham, United Kingdom
Duration: 16 Apr 201317 Apr 2013


ConferenceBritish Society of Animal Science Annual Meeting
Country/TerritoryUnited Kingdom


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