Age at first calving in dairy cows: which months do you aim for to maximise productivity?

a Knowledge Summary by

Mike Steele BSc(Hons), BVSc, MRCVS ^1*

¹Inspire Cattle Solutions, 10 Granborough Road, Winslow, Buckinghamshire, MK18 3BP
^*Corresponding Author (mike@dairyconsulting.vet)

Clinical scenario

The age at which a cow calves for the first time is a key indicator of the quality of youngstock management. Rate of growth in the heifer until she is inseminated, conceives and subsequently calves 9 months later can be affected by many factors. Nutrition quality and availability, disease risk (including parasitism), breed and insemination practices being only some of these influencing factors (Adamczyk, 2017; Bond, 2015; Davis Rincker, 2011 and MacDonald, 2005). A recent review of UK dairy herd data showed that the average (mean) age at first calving (AFC) was 29 months (median 28 months) (Eastham, 2018). This seemed significantly greater than the target of 22–24 months that is often quoted in press. Although there have been publications to summarise the performance effects of varying the AFC, few have concentrated on yield and reproduction together, in the same article and included data from more than one country.

The evidence

There are 17 articles recorded in this Knowledge Summary. They reflect a geographical range representative of Holstein-Friesian (Bos taurus) dairy cows in Europe, Asia and North America. There is one review of case series articles, including 125 referenced articles from 1979–2014. There is one randomised control trial, focusing on growth rates and AFC. The other 15 papers are case series, including data collected from dairy software on farms mostly involving dairy herd improvement (DHI) schemes. These include data from at least 2,645,158 cow records (one paper from Iran does not publish the number of cows in the dataset but describes the data as originating from 12 large farms and defines large farms in Iran to include roughly 7,000 cows per farm). Correlations in data are largely indicated by linear regression and covariance analysis and the main findings reported have been stated when either significant or no significant difference was observed at p-values of <0.05.

Summary of the evidence

Of the 17 articles discussed in this Knowledge Summary, the reported range of AFC is from 18 months old to 42 months old. The mean average AFC reported in each study differs by country, with Iran and USA at 25.5 months and UK at 29 months (Ettema J.F. 2004) (Elahi Torshizi M. 2016). Papers from other European countries do not report mean average but describe a commonly recorded AFC on farm, to be between 26 and 30 months (Krpalkova, 2014 and Pirlo, 2011). As mentioned in the methodology section, this Knowledge Summary has reflected the PICO and is not focused on the influencing factors of AFC but it is worth noting that major inputs to AFC include diet (intensive rearing or less intensive, both preweaning and post-weaning) and insemination procedures. Obviously, AFC reflects the gestation length of cattle (9 months) and insemination depends on animals reaching puberty and cycling healthy, viable ova. Wathes (2014) states that the onset of puberty can occur from 10 months and can be brought forwards by intensive rearing management and diets (Chester-Jones, 2017). Chester-Jones (2017) also notes that to maximise the occurrence of healthy ova, at least three cycles should be allowed before inseminaton should be practised.

Optimum range of AFC

The optimum range of AFC varies according to paper, outcome studied and geographical region but a consensus can be seen in overlapping months:

• 18–23 months (Banos, 2007): This range is inclusive of all data from 18–23 months and not considering data from each month separately
• 22 months (Eastham, 2018)
• 5–23.5 months (Changee, 2013)
• 22–24 months (Pirlo, 2011 and Nilforooshan, 2004)
• 22–26 months (Elahi Torshizi, 2016)
• 23–25 months (Ettema, 2004)
• <24 months (Adamczyk, 2017)
• 5 months (Krpalkova, 2014)
• 25–­26 months (Storli, 2017)

In summary, most papers agree that from their observations that the optimum AFC falls between 22–25 months inclusive. Beyond this in either direction, there appear to be detrimental consequences on one or more of the outcome effects reported below.

The effects of varying AFC have fallen mainly into 4 categories:

1. Milk Yield (first lactation 305 day yield; lifetime yield)
2. Fertility (first service conception rate; calving interval, days open, inseminations per pregnancy)
3. Longevity (survival to second calving and overall survival length)
4. Economic Return (return on rearing cost; loss/month compared to other AFC groups)

Consequently, each will be reported as a separate effect below:

Milk Yield

Milk yield (MY) has been measured as the volume of milk harvested from the cow in the 305 day lactation following her first calving (taken by addition of test-day results, daily milk weights or predicted 305 day yield in papers where yield was recorded over less than 305 days). Prediction of 305 day milk equivalent is a common parameter from dairy software recording systems that use equations linked to prediction of the lactation curve. Cows at certain days in milk (DIM) can have known monthly test day results to base a prediction figure from and calculate their predicted yield to the end of that lactation. Another parameter reported has been in MY from the cow over her total productive lifetime (either in total milk volume or average daily yield).

In terms of volume, milk losses and gains can be regarded from the perspective of pre-22 months; 22–25 months and post 25 months AFC. At an AFC of less than 22 months, 590–800 kg losses in the first 305 day lactation have been reported by (Elahi Torshizi, 2016) and (Pirlo, 2011). Ettema (2004) included pre-23 months in his study and reports a 320 kg loss in the first lactation: the lower volume lost is most likely because the cows at 22–23 months were included in the calculation. Only one study reports higher yields in 18–23 months, quoting 4.5% more milk from the first 305 day lactation (Banos, 2007). Cows with an AFC of greater than 25 months are also reported to have lower milk yields. Elahi Torshizi (2016) and Pirlo (2011) report a 170–600 kg loss in milk above 26 months. Berry (2009) reported that first lactation 305 day yield decreases by 55.5 kg less per month, increasing from 22 months AFC to 38 months. Cows calving between 22–25 months have been found to produce 2.1–2.4 kg/day more milk than their counterparts calving outside this window of time (Storli, 2017 and Eastham, 2018).

In summary, there appear to be lower milk yields of between 170 and 600 kg in the first lactation in cows with low AFCs (18–21 months) and 590–800 kg less yield in cows with high AFCs (>26 months).

Fertility

There is less clarity over fertility effects of varying age at first calving, mainly due to the parameters that researchers have measured on performance of reproduction. This is discussed in the appraisal section below. First service conception rate was reported by Ettema (2004) to be highest in AFC of <23, then 23–25, then >25 months (75%, 64%, 45%). Conversely, days open and calving interval have been reported as improving in older AFC groups (>26 months) compared to AFCs of <26 months (Eastham, 2018) and (Krpalkova, 2014). Banos, (2007) suggested that fertility would be compromised in younger AFC cattle by reporting 7% more inseminations per pregnancy and 7.5% higher return rate in AFC between 18–23 months.

In summary, although more papers suggest higher fertility rates in older AFC cattle, one key paper reflects that aiming for lower AFC does not compromise first service conception rate targets (Ettema, 2004).

Longevity

There has been no significant, direct effect of AFC on the survival length of cattle reported Nilforooshan (2004 and Wathes (2014). However, it must be noted that longevity of cattle is strongly linked to productivity and less productive cattle are more likely to be culled. Therefore, links can be made between AFC and survivability: Eastham (2018) suggests that cows calving between 22–26 months old are more likely to survive to calve a second time but this is not a reflection of the AFC itself but rather the management of transition and early lactation as a whole.

Profitability

Whether or not AFC affects the profitability of a dairy is a difficult and highly variable parameter to calculate, as so many factors in the management of both heifer rearing and lactation affect dairy profit. However, five of the reviewed papers have attempted to associate AFC with profitability. The longer it takes for a heifer to enter the milking herd, the more feed and management costs are involved in rearing her. Ettema (2004) observed that an AFC of 22–24 months was US$98–138 preferable per heifer than other AFCs. Pirlo (2011) calculated that an AFC of 22–26 months improved income per heifer by US$24–41 over other AFCs and Changee (2013) reported that an AFC of 22.5 months gave up to US$727 higher lifetime returns compared to an AFC of 32 months. Krpalkova (2014) suggests that between 24–26 months of AFC returns the highest profitability but does not state the amount: the statement is based on higher milk returns and fertility parameters. Wathes (2014) simply reviews the above papers.

In summary, it seems that an AFC of between 22–26 months produces the highest returns compared to lower or higher AFCs.

Acronyms

ADWG = average daily weight gain

AFC = age at first calving

BCS = body condition score

BW = body weight

CP = crude protein

ECM = energy corrected milk

DHI = dairy herd improvement

DIM = days in milk

DM = dry matter

HOL/FR = Holstein-Friesian

MY = milk yield

SCC = somatic cell count

SCS = somatic cell score

SD = standard deviation

Appraisal, application and reflection

Appraisal of papers

This Knowledge Summary includes 17 papers from 10 countries: four from USA; three from Iran; three from UK and one each from Korea, Ireland, Italy, Poland, Czech Republic, Norway and Australia. Together, they include over 2,645,158 cow records in 15 case series, one randomised control trial and one review. They cover scientific literature published from 1979–2018 (pre-2000 references coming from Wathes et al. (2014). Case series mostly include data taken from large farms with computerised dairy records. Many of these include farms on DHI programs (Elahi Torshizi,  2016 and Ettema & Santos, 2004) and cover data spreading over 2–5 years (Berry & Cromie, 2009; Eastham et al., 2018 and Nilforooshan & Edriss, 2004). Although this technique gives large sample population numbers, it may also create confounding factors: farms that use computer records and that participate in herd improvement schemes may not be representative of all dairy farms and are already skewing data towards the more advanced farm management systems. Therefore the AFCs recorded as the range within the country may be lower than the real picture. Also, if data from farms on improvement programs cover several years, it may be likely that the AFC and yields (and diets, disease management, heat abatement, etc.) may improve anyway, also confounding results.

Outcomes of AFC

Generally, MY data is well recorded on farms, as it represents the main form of income to the businesses. Only one of the reviewed papers mention the confounding effect of BW at calving on first lactation 305 day yield (Ettema & Santos, 2004). As AFC also influences first lactation 305 day yield, further research including this parameter would be preferable in future to attempt to separate these effects.

In contrast, fertility data is not so clear. Some papers use calving interval (the mean average between calvings in days); some use days open (the average number of days from calving to confirmed pregnancy) and others use first service conception rate (percentage of cows pregnant to the first service after voluntary waiting period). Unfortunately, calving interval is a very historical parameter: it generally represents cows that got pregnant at least 9 months to 1 year previous to the date it is recorded. Therefore, when measuring AFC effects in calving interval, the records may not be representative of the AFC group from the year studied, or include the confounding effect of culling in calculating calving intervals. Similarly, days open requires at least 85–120 days from calving to calculate a figure, so to be representative of the sample population, it must be recorded over at least a year. Again, this means that the AFC recorded may not be the same group of those providing the days open result. Also, when assessing improvements in days open, one must consider that it will go up before it goes down: only non-pregnant cows are included in the calculation: when a cow gets pregnant, she is removed from the “pool” of animals contributing to the data. Therefore, if more cows get pregnant, the pool of non-pregnant animals is skewed to a larger figure as it is more influenced by chronically non-pregnant cows. When these leave the population, the days open figure will finally go down but this may be a long time from the AFC figure recorded from the farm.

So the more representative figure for testing AFC is the first service conception rate used in Ettema & Santos (2004) compared to calving interval and days open used in Krpalkova (2014) and Eastham et al. (2018).

Two papers showed an influence on longevity from AFC, with those calving in the 24 month window having a high odds ratio of surviving their first lactation of 0.8–1.0 and those calving later, beyond 28 months having an odds ratio of <0.72 (Eastham et al. 2018 and Berry & Cromie, 2009). Others found no significant, direct effect. Survival in dairy cows is strongly influenced by productivity: whether this is from low yields, low fertility or presence of disease. AFC is linked to lower yields in ranges outside of 22–26 months, which could influence a culling decision but this decision may be more likely to be made from one of the other factors first.

As far as profitability is concerned, in order to calculate the effect of AFC on yield and fertility, a considerable amount of modelling is required. There is a lot of potential here for different researchers to include different parameters into their model: feed prices change by country and over time, as does economy in general, therefore the conclusion of one paper may not be comparable with another. As the effects of AFC (yield, fertility and culling) are influenced by so many other factors, the model is required to have many inputs, from labour, feed price, veterinary costs, rent, energy costs, disease rates, etc. When this is calculated, it is easy for some groups to miss some inputs and also, without considerable detail, avoid double-counting. For this reason, it is not advisable to take a value published from these papers and directly translate that to the reader’s situation.

Application and reflection

The clinical bottom line has far-reaching consequences for advisors on dairy farms. AFC is a key performance indicator of heifer management, including diet quality and availability, disease risk, insemination techniques and preweaning growth. A knowledge of the evidence that sets a target window of 22–26 months is a crucial tool in youngstock management advice. Not reaching these goals can be detrimental to both fertility and milk income, so hitting these targets gives both foundation and drive to improvement projects throughout the industry.

Further research in the interaction of body weight at birth and AFC on first lactation yield would provide more clarity on the individual effects of both on production.

Methodology Section

Three databases were used to search this PICO. The author has chosen to exclude papers before 2000, as dairy records before this date were limited and the management/genetics of dairy cows since this date have changed considerably in many countries through improvement schemes. One review Wathes et al. (2014) mentions papers back to 1979 and is a comprehensive work summarising much of the intervening period, so as it is included in this review, it was felt by the author to be a sufficient summary of the evidence pre-2000.

The PICO focused on effects rather than inputs to AFC so articles were excluded that concentrated on influences on AFC rather than consequences of varying AFC.

There have been publications linking AFC to genetic heritability traits, as this is an attractive theme to offer from genetic improvement (semen) companies. However, it has been evident from the literature that heritability of AFC is very low and not a significant factor (Ruiz-Sanchez et al. 2007): many other publications also make this conclusion. For this reason, the author has excluded genetic heritability papers from the Knowledge Summary.

Search Strategy
Databases searched and dates covered:	PubMed (NCBI) February 28th 2019; CAB Abstracts March 1st 2019; Google Scholar March 1st 2019). Filtered from 2000 to 2019
Search strategy:	Using Advanced Search keywords on words based only in the PICO topic PubMed: ((((((bovi* OR cattle OR cow$ OR heifer))) AND (([age at first calving] OR AFC OR [calving age])))) AND milk) AND ((yield OR volume OR weight)) AND ("2000/01/01"[PDat] : "2019/12/31"[PDat]) CAB Abstracts: (cattle OR cow$ OR heifer OR bovi*) AND ([age at first calving] OR AFC ) AND ( yield OR production OR lactation) AND (reproduc* OR fertility) Limiters: Scholarly (Peer Reviewed) Journals; Date of Publication: 20000101-20191231 Google Scholar: (cattle OR cow$ OR heifer OR bovi*) AND ([age at first calving] OR AFC) AND (yield OR production OR lactation) AND (reproduc* OR fertility). Date of publication: Last 10 years
Dates searches performed:	Date search performed 28/02/2019 and 01/03/2019

Exclusion / Inclusion Criteria
Exclusion:	Pre-2000. Heifer management and breeds of Holstein Dairy cattle have changed significantly since 2000 as dairies across the world increasingly use computer software and targeted strategies. Bos taurus only Papers concentrating on growth rates in youngstock and AFC Papers concentrating on nutritional protocols in youngstock and AFC
Inclusion:	Associations between AFC and yield or reproduction in Bos taurus dairy cattle Assessments of factors affecting AFC and performance Any breed reported (not restricted to Holstein-Friesian) but mentioned in the population studied sections Peer-reviewed papers only

Search Outcome
Database	Number of results	Excluded – pre 2000	Excluded – non-relevance to PICO	Excluded – related to factors before calving rather than AFC	Total relevant papers
PubMed	472	91	362	4	15
CAB abstracts	677	296	359	14	8
Google Scholar	201	76	118	3	4
Total relevant papers when duplicates removed					17

The author declares no conflicts of interest.

1. Adamczyk, K., Makulska, J., Jagusiak, W. & Węglarz, A. 2017. Associations between strain, herd size, age at first calving, culling reason and lifetime performance characteristics in Holstein-Friesian cows. Animal 11 (2): 327–334. DOI: http://dx.doi.org/10.1017/S1751731116001348
2. Banos, G., Brotherstone, S. & Coffey, M.P. 2007. Prenatal maternal effects on body condition score, female fertility, and milk yield of dairy cows. Journal of Dairy Science 90 (7): 3490–3499. DOI: http://dx.doi.org/10.3168/jds.2006-809
3. Berry, D.P. & Cromie, A.R. 2009. Associations between age at first calving and subsequent performance in Irish spring calving Holstein–Friesian dairy cows. Livestock Science 123 (1): 44–54. DOI: http://dx.doi.org/10.1016/j.livsci.2008.10.005
4. Bond, G.B., von Keyserlingk, M.A., Chapinal, N., Pajor, E.A. & Weary, D.M. 2015. Among farm variation in heifer BW gains. Animal 9 (11): 1884–1887. DOI: http://dx.doi.org/10.1017/S175173111500097X
5. Changhee, D., Nidarshani, W., Kwanghyun, C., Yunho, C., Taejeong, C., Byungho, P. & Donghee, L. 2013. The Effect of Age at First Calving and Calving Interval on Productive Life and Lifetime Profit in Korean Holstein. Asian Autralasian Journal of Animal Science 26 (11): 1511–1517. DOI: https://doi.org/10.5713/ajas.2013.13105
6. Chester-Jones, H., Heins, B.J., Ziegler, D., Schimek, D., Schuling, S., Ziegler, B., de Ondarza, B., Sniffen, C.J. & Broadwater, N. 2017. Relationships between early-life growth, intake, and birth season with first-lactation performance of Holstein dairy cows. Journal of Dairy Science 100 (5): 3697–3704. DOI: http://dx.doi.org/10.3168/jds.2016-12229
7. Davis Rincker, L.E., Vandehaar, M.J., Wolf, C.A., Liesman, J.S., Chapin, L.T. & Weber Nielsen, M.S. 2011. Effect of intensified feeding of heifer calves on growth, pubertal age, calving age, milk yield, and economics. Journal of Dairy Science 94 (7): 3554–3567. DOI: http://dx.doi.org/10.3168/jds.2010-3923
8. Eastham, N.T., Coates, A., Cripps, P., Richardson, H., Smith, R. & Oikonomou, G. 2018. Associations between age at first calving and subsequent lactation performance in UK Holstein and Holstein-Friesian dairy cows. PlosOne 13 (6): e0197764. DOI: http://dx.doi.org/10.1371/journal.pone.0197764
9. Elahi Torshizi, M. 2016. Effects of season and age at first calving on genetic and phenotypic characteristics of lactation curve parameters in Holstein cows. Journal of Animal Science and Technology 58 (8): doi: 10.1186/s40781-016-0089-1. DOI: http://dx.doi.org/10.1186/s40781-016-0089-1
10. Ettema, J.F. & Santos, J.E. 2004. Impact of age at calving on lactation, reproduction, health, and income in first-parity Holsteins on commercial farms. Journal of Dairy Science 87 (8): 2730–2742. DOI: http://dx.doi.org/10.3168/jds.S0022-0302(04)73400-1
11. Haworth, G.M., Tranter, W.P., Chuck, J.N., Cheng, Z. & Wathes, D.C. 2008. Relationships between age at first calving and first lactation milk yield, and lifetime productivity and longevity in dairy cows. Veterinary Record 162 (20): 643–647. DOI: http://dx.doi.org/10.1136/vr.162.20.643
12. Krpalkova, L., Cabrera, V.E., Kvapilik, J., Burdych, J. & Crump, P. 2014. Associations between age at first calving, rearing average daily weight gain, herd milk yield and dairy herd production, reproduction, and profitability. Journal of Dairy Science 97 (10): 6573–6582. DOI: http://dx.doi.org/10.3168/jds.2013-7497
13. MacDonald, K.A., Penno, J.W., Bryant, A.M. & Roche, J.R. 2005. Effect of feeding level pre- and post-puberty and body weight at first calving on growth, milk production, and fertility in grazing dairy cows. Journal of Dairy Science 88 (9): 3363–3375. DOI: http://dx.doi.org/10.3168/jds.S0022-0302(05)73020-4
14. Nilforooshan, M.A. & Edriss, M.A. 2004. Effect of age at first calving on some productive and longevity traits in Iranian Holsteins of the Isfahan province. Journal of Dairy Science 87 (7): 2130–2135. DOI: http://dx.doi.org/10.3168/jds.S0022-0302(04)70032-6
15. Pirlo, G., Miglior, F. & Speroni, M. 2011. Effect of age at first calving on production traits and on difference between milk yield returns and rearing costs in Italian Holsteins. Journal of Dairy Science 83 (3): 603–608. DOI: http://dx.doi.org/10.3168/jds.S0022-0302(00)74919-8
16. Ruiz-Sanchez, R., Blake, R.W., Castro-Gamez, H.M.A., Sanchez, F., Montaldo, H.H. & Castillo-Juarez, H. 2007. Changes in the Association Between Milk Yield and Age at First Calving in Holstein Cows with Herd Environment Level for Milk Yield. Journal of Dairy Science 90: 4830–4837. DOI: http://dx.doi.org/10.3168/jds.2007-0156
17. Sadeghi-Sefidmazgi, A., Moradi-Shahrbabak, M., Nejati-Javaremi, A., Miraei-Ashtiani, S.R. & Amer, P.R. 2012. Breeding objectives for Holstein dairy cattle in Iran. Journal of Dairy Science 95: 3406–3418. DOI: http://dx.doi.org/10.3168/jds.2011-4573
18. Storli, K.S., Klemetsdal, G., Volden, H. & Salte, R. 2017. The relationship between Norwegian Red heifer growth and their first-lactation test-day milk yield: A field study. Journal of Dairy Science 100 (9): 7602–7612. DOI: http://dx.doi.org/10.3168/jds.2016-12018
19. Wathes, D.C., Pollot, G.E., Johnson, K.F., Richardson, H. & Cooke, J.S. 2014. Heifer fertility and carry over consequences for life time production in dairy and beef cattle. Animal 8 (1): 91–104. DOI: http://dx.doi.org/10.1017/S1751731114000755